Hydrology Report - s3-eu-west-1.amazonaws.com · Hydrology Report i Checking and Approval Prepared by: Scott Baigent, Senior Hydrologist Linda Hemsley, Hydrologist Paul Dunne, Assistant

Hydrology Report February 2009

Lee Catchment Flood Risk Assessment and Management Study

Hydrology Report

i

Checking and Approval

Prepared by:

Scott Baigent, Senior Hydrologist

Linda Hemsley, Hydrologist

Paul Dunne, Assistant Project Manager

15 Apr 2008

Checked by:

M Clare Dewar

25 Feb 2009 Project Manager

Approved by:

Richard Crowder

25 Feb 2009 Project Director

Contents amendment record

Issue Revision Description Date Signed

0 1 Draft table of contents for comment June 07 MCD

1 0 Draft to OPW for comment Nov 07 MCD

2 0 Final Report Feb 08 MCD

3 0 Final Report following OPW comments April 08 MCD

3 1 Final Report with updated MRFS flows Feb 09 MCD

Halcrow Group Ireland Ltd has prepared this report in accordance with the instructions of the Office of Public Works for their sole and specific use. Any other persons who use any information contained herein do so at their own risk.

Halcrow Group Ireland Limited 3A Eastgate Road, Eastgate, Little Island, Cork Tel +353 21 452 4418 Fax +353 21 452 4419 www.halcrow.com

© Halcrow Group Ireland Limited 2009


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Acknowledgements

The Lee Catchment Flood Risk Assessment and Management Strategy is being undertaken by Halcrow Group Ireland Limited with support from MarCon Computation International Ltd, J B Barry & Partners Ltd and Brady Shipman Martin.

This hydrology report has been prepared by Halcrow Group Ltd and J B Barry & Partners Ltd. The meteorological and hydrological analyses presented in Sections 5 and 6 of this report were undertaken by J B Barry & Partners Ltd.

MarCon Computations International

Ltd

BRADY SHIPMAN MARTIN


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Executive Summary

The Office of Public Works and its partners, Cork City Council and Cork County Council, are undertaking a catchment-based flood risk assessment and management study of the Lee Catchment – the Lee Catchment Flood Risk Assessment and Management Study (CFRAMS). The main output from this study will be flood maps and a Catchment Flood Risk Management Plan, which will identify a programme of prioritised studies, actions and works to manage the flood risk in the Lee catchment in the long-term. The plan will also make recommendations in relation to appropriate development planning. The Lee CFRAMS is the primary pilot project for a new national approach to flood risk management.

This report details the hydrological assessment that has been undertaken for this study with the objective of determining hydrological inputs for the Lee and its tributaries for specific design events and future scenarios. This is based on a review and analysis of historic flood information and use of meteorological and hydrometric records. The Flood Studies Report (FSR) and Flood Estimation Handbook (FEH) methodologies have been used to enable determination of design hydrological inputs considering potential future catchment changes likely to influence flood risk. Hydraulic model calibration and verification events have been identified and integration of the hydrology and hydraulic modelling undertaken. The analysis presented in this report is concerned with the estimation of extreme flows, which will form the basis for subsequent flood level and mapping stages of the Lee CFRAMS.

An extensive review of historical flood related documents has highlighted that there are a number of urban and rural areas at risk of flooding within the Lee catchment from both tidal and fluvial flood mechanisms. Flow, rainfall and tidal gauge data from the catchment and historic flood documentation has allowed at least two calibration/verification events for five of the eight river models representing the main rivers and tributaries in the catchment to be generated. The Lee catchment was sub-divided into 56 sub-catchments in total to ensure representation of the hydrological processes in the catchment is at a scale and resolution appropriate to this study. Three types of hydrological inflows (hydrographs, steady flows and lateral flows) were identified to be used to feed into the hydraulic models; these included the use of lateral inflows in all urban areas to reduce uncertainty.

The study will identify both the existing risk and potential future risk of flooding to communities. There are a number of drivers that can influence future flood risk in the Lee catchment, the main drivers have been identified as being climate change, afforestation and urbanisation. These drivers have been extensively investigated and two future flood risk management scenarios have been proposed, a Mid Range Future Scenario and a High End Future Scenario.

The outputs from this hydrological assessment will inform the subsequent stages of this study, in particular the hydraulic modelling and flood mapping stages. Knowledge of the hydrological processes and historic flooding gained from this work will support the decision making process for the flood risk management options, including the potential of reviewing the operation of the hydroelectric dams before and during flood events.


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Table of contents

Checking and Approval ........................................................................................................... i

Contents amendment record................................................................................................... i

Acknowledgements................................................................................................................. ii

Executive Summary................................................................................................................ iii

Table of contents ..................................................................................................................... v

List of figures ......................................................................................................................... vii

List of tables............................................................................................................................ ix

Glossary ................................................................................................................................... x

1. Introduction................................................................................................................. 1

1.1. Background .............................................................................................................. 1

1.2. Objectives................................................................................................................. 1

1.3. Approach .................................................................................................................. 2

2. Data collection ............................................................................................................ 4

2.1. Introduction............................................................................................................... 4

2.2. Topographical data................................................................................................... 4

2.3. Hydrometric data ...................................................................................................... 5

2.4. Meteorological data .................................................................................................. 8

2.5. Tidal data.................................................................................................................. 8

2.6. Mapping data............................................................................................................ 9

3. Description of the Lee Catchment .......................................................................... 11

3.1. Upper Lee catchment ............................................................................................. 12

3.2. Lower Lee catchment ............................................................................................. 13

3.3. River Bride catchment ............................................................................................ 15

3.4. Glashaboy River catchment ................................................................................... 15

3.5. Carrigtohill catchment............................................................................................. 17

3.6. Owennacurra River catchment............................................................................... 18

3.7. Owenboy River catchment ..................................................................................... 19

3.8. Tramore River catchment....................................................................................... 20

3.9. Cork Harbour catchment ........................................................................................ 20


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3.10. Operation of Carrigadrohid and Inishcarra hydroelectric dams ............................. 21

4. Review and analysis of historic floods .................................................................. 24

4.1. Introduction............................................................................................................. 24

4.2. Flood events........................................................................................................... 24

4.3. Summary of Flood Mechanisms............................................................................. 24

4.4. Selection of calibration events ............................................................................... 26

5. Meteorology .............................................................................................................. 29

5.1. Overview ................................................................................................................ 29

5.2. Rainfall growth curves ............................................................................................ 29

5.3. Spatial Distribution of Extreme Rainfall.................................................................. 33

5.4. Historical climate change ....................................................................................... 36

6. Hydrology .................................................................................................................. 37

6.1. Rating curve review................................................................................................ 37

6.2. Index flood.............................................................................................................. 41

6.3. Pooled hydrology growth curve.............................................................................. 49

6.4. Calibration hydrology.............................................................................................. 54

6.5. Design hydrology.................................................................................................... 61

6.6. Sensitivity to changes in catchment parameters.................................................... 66

7. Integration of hydrology and hydraulic modelling................................................ 69

7.1. Sub-catchment delineation..................................................................................... 69

7.2. Hydraulic model inflows.......................................................................................... 70

8. Future environmental and catchment changes..................................................... 72

8.1. Introduction............................................................................................................. 72

8.2. Climate change ...................................................................................................... 72

8.3. Afforestation ........................................................................................................... 77

8.4. Urbanisation ........................................................................................................... 80

8.5. Future scenarios for flood risk management.......................................................... 83

8.6. Inclusion of confidence limits in Lee CFRAMS ...................................................... 86

8.7. Policy to aid flood reduction ................................................................................... 86

9. Summary and recommendations............................................................................ 88


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References ............................................................................................................................. 91

Appendix A Data collection

Appendix B Historical flood events

Appendix C Meteorological analysis

Appendix D Hydrological analysis

Appendix E Integration of hydrology and hydraulic modelling

Appendix F Future drivers of flood risk

List of figures

Figure 1-1 The Lee catchment .............................................................................................. 1

Figure 2-1 Location map of the hydrometric and tidal gauges in the Lee catchment ........... 7

Figure 2-2 Location of rainfall gauges ................................................................................... 8

Figure 3-1 The nine subcatchments of the Lee catchment ................................................. 11

Figure 3-2 Upper Lee catchment broken down into 8 subcatchments................................ 12

Figure 3-3 Lower Lee catchment broken down into fifteen subcatchments........................ 14

Figure 3-4 River Bride catchment broken down into three subcatchments ........................ 15

Figure 3-5 Glashaboy River broken down into five subcatchments.................................... 16

Figure 3-7 Owennacurra catchment broken down into 6 subcatchments........................... 18

Figure 3-8 Owenboy River catchment broken down into ten subcatchments..................... 19

Figure 3-10 Cork Harbour catchment.................................................................................... 21

Figure 4-1 Seasonality of historic tidal and fluvial floods in the Lee catchment.................. 25

Figure 4-2 Recommended locations for additional meteorological and hydrometric gauges . ........................................................................................................................... 27

Figure 5-1 Lee quartile analysis compared to FSR England/Wales and Scotland/ Northern Ireland growth curves (to M5-2Day class 60-75mm)............................................................... 31

Figure 5-2 Lee quartile analysis compared to FSR England/Wales and Scotland/ Northern Ireland growth curves (to M5-2Day class 75mm-100mm)....................................................... 32

Figure 5-3 Lee quartile analysis compared to FSR England/Wales and Scotland/ Northern Ireland growth curves (to M5-2Day class 100 – 150mm)........................................................ 32

Figure 5-4 M5-2Day. Lee-CFRAMS compared with FSR ................................................... 34

Figure 5-5 M5-2Day. Lee-CFRAMS compared with preliminary FSU (based on meteorological data to June 2006) .......................................................................................... 34


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Figure 5-6 Jenkinson’s Ratio. Lee-CFRAMS and preliminary FSU (based on meteorological data to June 2006) .......................................................................................... 35

Figure 5-7 AAR values for the Lee catchment (based on meteorological data to June 2006) 35

Figure 5-8 Temporal changes in annual maximum rainfall ................................................. 36

Figure 6-1 Location of the 11 gauges for the rating curve review....................................... 39

Figure 6-2 Revised rating curve for gauge 19020............................................................... 40

Figure 6-3 Regional Qmed Relationship ............................................................................... 43

Figure 6-4 Ungauged catchment methodology ................................................................... 45

Figure 6-5 Catchment SPR scale factors............................................................................ 46

Figure 6-6 Study Qmed 95 percentile confidence limits........................................................ 48

Figure 6-7 Hydrometric gauge L-Moment ratio diagram compared with theoretical GEV and GL distributions........................................................................................................................ 50

Figure 6-8 Site indexed annual maximum floods compared with pooled growth curve and the FSR Ireland growth curve.................................................................................................. 51

Figure 6-9 Pooled growth curve and 95%ile confidence limits in relation to FSR Ireland growth curve ........................................................................................................................... 52

Figure 6-10 Study growth curve with 95%ile confidence limit ............................................... 53

Figure 6-11 Averaged Unit Hydrographs at Lee Hydrometric Gauges Compared with Flood Studies Report Unit Hydrograph.............................................................................................. 62

Figure 6-12 Sub catchment unit hydrograph catchment characteristics based on sub catchment area. ....................................................................................................................... 64

Figure 6-13 Sub catchment unit hydrograph catchment characteristics based on urban fraction ....................................................................................................................... 64

Figure 6-14 Sub catchment unit hydrograph catchment characteristics based on SPR (before donor catchment scaling) ............................................................................................ 64

Figure 6-15 Sub catchment unit hydrograph catchment characteristics based on SPR (after donor catchment scaling). ....................................................................................................... 65

Figure 6-16 Change in maximum design rainfall as a result of 20% change in SPR........... 67

Figure 6-17 Change in maximum design rainfall as a result of 20% change in CWI ........... 67

Figure 6-18 Change in maximum design rainfall as a result of 20% change in M5-2Day rainfall ....................................................................................................................... 67

Figure 6-19 Change in maximum design rainfall as a result of 20% change in urban fraction 68

Figure 7-1 Sub-catchment delineation ................................................................................ 70

Figure 7-2 Example of integration of hydrology and hydraulic modelling for the Owenboy hydraulic model ....................................................................................................................... 71


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Figure 8-1 Landscape character areas within the catchment (Source: Cork County Council) ........................................................................................................................... 78

Figure 8-2 Existing urban development in the Lee catchment (based on year 2000 Corine data) ........................................................................................................................... 81

Figure 8-3 Future development in Lee catchment [to time horizon 2020] .......................... 82

List of tables

Table 2-1 Datasets for tidal and surge modelling ................................................................ 9

Table 2-2 Datasets for tidal and surge modelling ................................................................ 9

Table 4-1: Significant recent events in the Lee Catchment ................................................ 25

Table 4-2 Possible calibration/verification events for the Lee and tributaries.................... 26

Table 5-1 Meteorological Station Records to June 2006................................................... 30

Table 6-1 Details of the gauging stations used in the rating curve review......................... 38

Table 6-2 Revised rating equation values for gauge 19020. Flow Q is calculated using the equation Q(h)=C*(h+a)^b. The parameters for the equation are obtained from the table below for varying stages in water depth h.......................................................................................... 41

Table 6-3 Gauged Qmed...................................................................................................... 44

Table 6-4 Study growth factors .......................................................................................... 53

Table 6-5: Actual calibration/verification events for the Lee and tributaries ....................... 60

Table 6-6: Detail of availability of flow gauge data for calibration events ........................... 61

Table 6-7 Study flood-storm return period relationship compared with the Flood Studies Report ........................................................................................................................... 63

Table 6-8 Confidence limit scaling factor ........................................................................... 66

Table 7-1 Breakdown of hydrographs and inflows per hydraulic model ............................ 71

Table 8-1 Land movement (cm) estimates applicable for the Lee CFRAMS from UK literature sources for three future time horizons (baseline for calculating land movement for a given year is taken from 1990). ............................................................................................... 75

Table 8-2 Sea level rise (cm) estimates applicable for the Lee CFRAMS from various UK and Irish literature sources for three future time horizons ....................................................... 76

Table 8-3 Estimates of increase in precipitation (%) applicable to the Lee CFRAMS from various UK and Irish sources for three future time horizons ................................................... 77

Table 8-4 Future afforestation stages – hydrology parameters ......................................... 80

Table 8-5 Future urban development scenarios – hydrology parameters ......................... 83

Table 8-6 Relevant combinations of drivers to provide boundaries for future flood risk.... 84


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Glossary

Term used Explanation

A Catchment Area (km2)

Annual Exceedance

Probability (AEP)

The probability that an event of a specified magnitude will be exceeded in any given year

ANSF Baseflow (m3/s/km2)

AquilaDSF Software tool providing users with the capability to investigate the environmental and socio-economic impacts of changes in the quantity and the quality of flows in a river system brought about by changing circumstances within the river catchment

ARF Areal Reduction Factor

Catchment The total area of land that drains into a watercourse

CWI Catchment Wetness Index (averaged to 125mm for study area based on FSR Vol 1 Figure 6.44) (mm)

Digital Elevation Model

(DEM)

A digital representation of the ground surface topography including buildings and vegetation

Digital Terrain Model

(DTM)

A bare earth model of the ground which has all the buildings and vegetation removed

DPRCWI Dynamic Percentage Runoff based on catchment wetness

Flood Estimation

Handbook *(FEH)

Publication giving guidance on rainfall and river flood frequency estimation in the UK

Flood Studies Report

(FSR)

Current industry standard for flood studies in Ireland

Floodplain The land adjacent to a stream or river that experiences occasional or periodic flooding

Fluvial Related to a river or a stream

Gauged catchment Catchments in which river flows are measured through the use of a gauge.

Geographical Information

Systems (GIS)

Software tools used for, storing, analyzing and managing data and associated attributes which are spatially referenced to the earth.


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GEV Generalised Extreme Value Distribution, consisting of EV1, EV2 and EV3 distributions

GL Generalised Logistic Distribution

High Resolution Stereo

Camera (HRSC)

An airborne mapping technique which uses a High Resolution Stereo Camera to capture imaging and 3D data which is used to generate a digital terrain model

Hydrograph A plot of the discharge of water as a function of time.

ISIS 1-D computational hydraulic model developed by Halcrow and HR Wallingford

ISIS Reservoir unit ISIS computer model unit used to model floodplain storage. In an unsteady model, it will ensure conservation of mass so that, for example, the overbank spills from a channel are accounted for and may drain back into the main channel as the flood subsides.

Jenkinson’s Ratio Ratio or percentage of (M5-1hr)/(M5-2Day)

Light Detection and

Ranging (LIDAR)

An airborne mapping technique which uses a laser to measure the distance between the aircraft and the ground to produce a digital terrain map of the catchment

M5-2Day 5 year return period, 2 day duration rainfall (mm)

M5-D 5 year return period, D duration rainfall (mm)

MSL Mean Stream Length (km)

MT-D T year return period, D duration rainfall (mm)

Normal depth downstream

boundary

ISIS computer model unit which enables the user to specify a downstream boundary which automatically generates a flow-head relationship based on cross section data.

P Rainfall Depth (mm)

PRRURAL Percentage Runoff of catchment rural component

PRTOTAL Total Percentage runoff, inclusive of rural, urban and catchment wetness contributions


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Q1 water levels Water level data recorded at random time intervals.

Q15 water levels Continuous water level data recorded at 15 minute intervals

Qmax Maximum annual water levels

Return period Measurement indicating the likelihood of a flood event of a certain intensity occurring or being exceeded in any given year

S1085 Averaged stream slope, based on points 10% and 85% along stream length (m/km)

S1-S5 Proportion of catchment area contained in the corresponding FSR Winter Rainfall Acceptance Potential category.

AAR Annual Average Rainfall (mm)

SPR Standard Percentage Runoff

T Unit Hydrograph Time Step Interval

Tp Time to Peak (hr)

Ungauged catchment Catchment in which there is no gauge to measure river flows

Urban Fraction of urban extent


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1. Introduction

1.1. Background

The Office of Public Works (OPW) commissioned Halcrow to undertake the Lee Catchment Flood Risk Assessment and Management Study (Lee CFRAMS) in August 2006. The Lee CFRAMS is the pilot flood risk assessment and management study in Ireland and will set a framework for future such studies in other catchments across the country.

There is a high level of flood risk in the Lee Catchment from the River Lee, its tributaries and Cork Harbour and a number of significant events have occurred in the past, including August 1986 (an extreme river flooding event) and March 1962 (serious tidal flooding event). The OPW and their partners for this study, Cork City and County Councils have recognised this risk and have commissioned this study as a means of understanding the flooding problem and managing the flood risk through the development of a Catchment Flood Risk Management Plan.

The Lee catchment is one of the largest catchments in the southwest of Ireland and covers an area of approximately 2,000km2 (Figure 1-1). The study encompasses the entire Lee catchment and includes Cork Harbour, the main watercourses and their estuaries, urban areas known to be at risk from flooding, and areas subject to significant development pressure both now and in the future. A full description of the Lee catchment is available in Section 3 of the report.

Figure 1-1 The Lee catchment

1.2. Objectives

As the primary pilot project for the OPW’s CFRAM Programme, the specific objectives of the Lee CFRAMS are to:


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• Assess and map the spatial extent and degree of flood hazard and risk in the catchment with particular focus on urban areas;

• Examine future pressures such as land use and climate changes that could increase the risk of flooding;

• Build the information base necessary for making informed decisions in relation to managing flood risk (including planning and development management);

• Carry out a Strategic Environmental Assessment (SEA). This will ensure that environmental issues and opportunities for enhancement are fully considered throughout the study; and

• Develop an economically, socially and environmentally appropriate long-term (a 50 to 100 year time frame) strategy (a Catchment Flood Risk Management Plan) for managing flood risk to help ensure the safety and sustainability of communities in the catchment

The Catchment Flood Risk Management Plan will include a programme of prioritised actions, measures and works (structural and non-structural) to manage the flood risk in the area in the long-term, and make recommendations in relation to appropriate development planning.

1.3. Approach

In order the meet the objectives set out in Section 1.2, an assessment of the hydrological processes within the catchment is required. The objectives and approach adopted for the hydrological assessment of the Lee catchment incorporates;

• review and analysis of historic flood information;

• identification of suitable calibration and verification flood events;

• use of meteorological and hydrometric records;

• appropriate use of Flood Studies Report (FSR) and Flood Estimation Handbook (FEH) methodologies to enable determination of design hydrological inputs;

• integration of hydrology with hydraulic modelling; and

• assessment of potential future catchment changes likely to influence flood risk.

The level of detail adopted ensures the representation of the likely runoff and river flows in the catchment, particularly urban areas, is at a scale and resolution appropriate to this study.

1.4. Technical approach overview

The analysis presented in this report is focused on the maximizing the accuracy of flood flow estimates. In subsequent stages of the Lee CFRAMS, the flood flows will be used in determining flood levels, flood extents and flood risk management options.

The technical approaches outlined in Sections 5 and 6 are concerned with maximizing the accuracy of the flood flow estimates. A statistical review was undertaken of records from nearby meteorological stations and improved the accuracy of standard Flood Studies Report (FSR) design rainfall mapping in the study area (Section 5). Similarly, a statistical review


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was undertaken of hydrometric records in the study catchment and used to calibrate FSR runoff characteristics (Section 6). The design flows were then generated from the calibrated runoff characteristics and corrected design rainfall.


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2. Data collection

2.1. Introduction

A significant amount of data was collected to provide the basis for undertaking the hydrological assessment. The data collected ranged from recorded rainfall and flow values in the catchment to anecdotal evidence of historic flood events and detailed GIS layers of land use within the catchment, and can be grouped under the following headings:

• Topographical data

• Hydrometric data

• Meteorological data

• Tidal data

• Mapping data

• Historic data

This section provides a summary of the data collected for the hydrological analysis which was received in a number of different formats. The majority of the hydrological data was uploaded to AquilaDSF, which was used by the project team for storing, visualising, assessing and distributing hydrological and meteorological data. Specific tools within the software were used for the derivation of unit hydrographs and the generation of the annual maximum series. GIS has been used for the spatial representation of a range of data sets, data storage, data analysis, data management, data calculation and graphical display.

A number of organisations and websites have been consulted to obtain the necessary data including Cork City Council, Cork County Council, EPA, ESB, OPW and Port of Cork. A list of contact organisations and a summary of the data available is outlined in Appendix A.

2.2. Topographical data

2.2.1. Hydrologically corrected DEM

A hydrologically corrected Digital Elevation Model (DEM) for the catchment was made available from the EPA. The hydrologically corrected DEM consists of a surface model of the catchment (20m grid cell resolution) which maintains sensible drainage conditions and allows transfer of water across the surface (Preston and Mills, 2002). The DEM was primarily used for the catchment and sub catchment delineation as described in Section 7.1.

2.2.2. Survey data

Maltby Land Surveys Ltd was commissioned by the OPW to survey cross-sections of the rivers and tributaries and relevant channel structures for input into hydraulic models of the rivers. The survey was carried out between March and June of 2007. The data was used in the hydrological analysis to develop hydraulic computer models for carrying out the rating curve review (Section 6.1).


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2.2.3. Floodplain DTM’s

The Digital Terrain Model (DTM) of the floodplain is a bare earth model of the ground which has all the buildings and vegetation removed. The DTM has a 2m grid cell resolution and was used in the development of the hydraulic models for the rating curve review. The DTM was generated from both Light Detection and Ranging (LiDAR) data and High Resolution Stereo Camera (HRSC) data.

Issues relating to the accuracy of the filtering process used to generate the DTM from the HRSC data arose during both the extraction of the floodplain cross sections and comparison with the LiDAR DTM. These accuracy concerns primarily related to DTM coverage of urban areas where buildings were not fully filtered from the raw data, however in the more rural areas the agreement between the two datasets is good. As the majority of the hydrometric gauges are located in rural areas it was decided to continue with the use of the HRSC data for the rating curve review (Section 6.1). It is recommended that rating curves developed using the HRSC data are revised at a future date to include the LiDAR data.

2.3. Hydrometric data

Hydrometric data was received from three organisations, namely the OPW, ESB and EPA. A summary of the data received from each organisation is outlined below. Figure 2-1 shows the location of the hydrometric gauges in the catchment. Appendix A4 contains information on the timescales of this data.

Hydrometric data has been received for four OPW hydrometric stations. Instantaneous 15 minute interval water level data, station ratings and applicable rating periods have been provided for the following four stations; 19001, 19044, 19045, 19046. Additionally spot gauge data and rating equations have been provided for gauge 19001 for the rating curve review.

Hydrometric data has been received from the EPA for the following stations and includes;

• Daily mean flows, Q1 flow values, Q15 flow values and water level data for the following seven hydrometric stations; 19005, 19006, 19009, 19017, 19018, 19020, 19022 and 19032.

• Rating curves for the hydrometric stations listed above plus rating curve data for the following additional hydrometric stations 19036, 19037, 19038, 19039, 19040, 19041, 19042 and 19043

• Spot gauge data and rating equations for gauges 19006, 19018 and 19020

Hydrometric data has been received from the ESB for twelve hydrometric gauges. This data was delivered in a number of different formats as detailed below:

• Q15 water level data has been received for gauges 19011, 19012, 19013, 19014, 19015, 19016, 19027, 19028, 19031, 19036, 19049 and 19050. This data was extracted from the ESB data loggers by the OPW and covers the period of record post 2002

• Q1 water level data has been made available for gauges 19011, 19012, 19013, 19014, 19015, 19016 and 19031. The data has been digitised from ESB chart data by the EPA and covers intermittent periods throughout the recorded data series


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• Qmax water level data is the annual maximum water level data which was manually extracted from the chart data by the ESB. This data covers all the following gauges; 19011, 19012, 19013, 19014, 19015, 19016, 19027, 19028 and 19031

• Spot gauge data and rating equations were provided in a hard copy format for all of the requested gauges. The data was scanned and digitised for the rating curve review

• Chart data was provided for a number of gauges for the following flood events: December 1978, August 1986 and November 2000. The data was digitised by Halcrow and used for the model calibration events (Section 3.4)

• Water level data from gauges within the reservoirs and tail races (19090, 19091, 19092 and 19093) and historical gate and spill settings for a limited number of past flood events have been made available by the ESB.

Analysis of the hydrometric data is included in Section 6 of the report.


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Figure 2-1 Location map of the hydrometric and tidal gauges in the Lee catchment


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2.4. Meteorological data

A request for meteorological data was sent to two organisations, namely Met Éireann and the OPW. Appendix A4 contains information on the period of record of the data made available. The ESB also operate six rain gauges in the catchment, however no data was requested for these gauges as awareness of the availability of this dataset did not provide sufficient time for its inclusion in the analysis. Figure 2-2 shows the location of the rainfall gauges.

Figure 2-2 Location of rainfall gauges

Met Éireann provided both daily rainfall data and hourly rainfall data. Daily rainfall was received for thirty gauging stations, with hourly rainfall data provided for two further stations at Roches Point and Cork Airport. Met Éireann advised that data from the Roches Point gauge post 1990 was not reliable, therefore a full record of this dataset is not available. Additional rainfall data was received for a number of gauges in the upper Lee catchment for calibration of the upper Lee hydraulic model for the December 2006 event.

Meteorological data was received for eight OPW gauging stations in the form of hourly rainfall data. The period of record for this data ranges from early 2005 to mid 2006.

2.5. Tidal data

Tidal gauge data was received from the following organisations; Port of Cork, Met Éireann, ESB, Marathon Oil and Cork City Council. Table 2-1 lists the data available from each of the organisations. Figure 2-1 shows the location of the tidal gauges.


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Table 2-1 Datasets for tidal and surge modelling

Dataset Ownership Time Period Format

Cobh TG Port of Cork 01/12/2000 – 23/03/2006 Electronic

Tivoli TG Port of Cork 01/01/2001 - 31/12/2005 Electronic

Marathon TG Met Éireann 24/06/2002 - 26/06/2006 Electronic

Marina TG ESB 10/10/1953 – 15/10/1990 Paper

Cork City TG Cork City Council Range of dates (1992-2001) Electronic

Access was also granted to a number of paper chart datasets by the Port of Cork (Table 2-2). These datasets have not been made available for analysis outside the offices of the Port of Cork.

Table 2-2 Datasets for tidal and surge modelling

Dataset Ownership Time Period Format

IFI/Net TG Port of Cork 22/08/1980 - 03/01/1986 Paper

IFI/NET TG Port of Cork 08/01/1992 - 16/03/1995 Paper

Cobh TG Port of Cork 01/01/1992 - 09/01/1995 Paper

Tivoli TG Port of Cork 09/07/1993 - 04/03/1996 Paper

Ringaskiddy TG Port of Cork 10/08/1995 - 22/02/2000 Paper

Cork City TG Port of Cork 30/11/1982 - 28/12/1984 Paper

Tidal data was used in the analysis of calibration events for the catchment (Section 4).

2.6. Mapping data

The following is a list of the main mapping datasets that have been used to inform the hydrological assessment of the Lee catchment:

• Subsoils and soils data was made available from the EPA. This data was used to inform the description of the catchments (Section 3) and in the analysis of the hydrometric data (Section 6).

• Corine land cover data (2000) was made available from the EPA. The data was primarily used in both the description of the catchments and in assessing the future environmental and catchment changes (Section 8).


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• Cork County and City development plan data was made available from both Cork County Council and Cork City Council. This data was primarily used in the assessment of future environmental and catchment changes.

• 50,000 scale and 5,000 scale raster maps were made available by the OPW. This data was used throughout the hydrological analysis to provide spatial representation of the various hydrological datasets and in the detailed analysis of specific sections such as the review and analysis of historic flood events (section 4) and the integration of hydrology and hydraulic modelling (Section 7).


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3. Description of the Lee Catchment

The Lee catchment covers an area of approximately 2,000km2 and includes all the main rivers and their tributaries draining into Cork Harbour. The River Lee is one of the largest rivers in southwest Ireland rising in the Shehy Mountains to the west and discharging into Cork Harbour to the east. The river and its main tributaries, the rivers Sullane, Laney, Dripsey, Bride and Shournagh drain a catchment of more than 1,100km2 upstream of Cork City. The river is partly controlled by the Carrigadrohid and Inishcarra hydroelectric dams owned by the ESB. The catchment also includes a number of smaller rivers and their estuaries that drain into Cork Harbour. These include the Glashaboy, Owennacurra and Owenboy Rivers.

To facilitate the hydrological assessment and hydraulic modelling of the catchment it has been broken down into nine subcatchments as listed below and shown in Figure 3-1.

(i) Upper Lee

(ii) Lower Lee

(iii) Tramore/Douglas Rivers

(iv) River Bride (north of Cork City)

(v) Glashaboy River

(vi) Owenacurra River

(vii) Carrigtohill area

(viii) Owenboy River

(ix) Cork Harbour area

Figure 3-1 The nine subcatchments of the Lee catchment


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3.1. Upper Lee catchment

The upper Lee catchment encompasses an area of 790km2 and extends from Inishcarra Dam westwards to the Shehy mountains. The catchment borders with County Kerry along the Derrynasaggart Mountains to the north and Bandon River Valley to the south. The main rivers in the catchment include the Lee, Sullane, Foherish, Laney and Dripsey. Land height varies from 649mAOD at Mullaghanish to 50mAOD at Inishcarra reservoir. For the hydrological analysis the upper Lee catchment has been broken down into eight subcatchments as shown in Figure 3-2. The subcatchment areas have been derived so as to provide detailed hydrological inputs into the upper Lee hydraulic model. Section 7 of the report contains further information on the integration of hydrology and hydraulic modelling.

Figure 3-2 Upper Lee catchment broken down into 8 subcatchments

The catchment uplands extend around the north and west perimeter of the catchment and consist primarily of exposed rock and sandstone till subsoils. The majority of the catchment is overlain with deep well drained mineral soils with areas of peaty topsoil and planket bogs in the uplands. Agricultural activities in the uplands consist mainly of hill grazing and forestry. Forest cover is largely of coniferous trees with pockets of transitional woodland. Towards the east of the catchment the lower more undulating ground provides better agricultural land with the majority of the land used for pastoral grazing. There are also pockets of arable land and transitional woodland. The subsoils in the lower catchment are predominantly sandstone till with pockets of sandstone sands & gravels and alluvium gravels.

Upper Lee catchment at the Gearagh


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The peat uplands and steep topography give a slightly elevated runoff potential as represented in Figures 6-3 and 6-5 in Section 6 of the report.

Based on analysis of meteorological data (Figure 5-7) the Annual Average Rainfall (AAR) for the catchment is 1450mm. The River Lee and the Sullane River are the primary watercourses draining this rainfall. Both rivers flow in a predominantly west east direction with the Sullane River draining the north of the catchment and the River Lee draining the south of the catchment. The land is characterised by glaciated steep sided river valleys intercepted with ridges of upland. The rivers are generally confined to narrow river valleys with the exception of the River Lee which opens out at the Gearagh to form a wide braided river valley. The River Laney and Foherish River drain the uplands to the north of the catchment to the Sullane River. Two dams control the flow of water from the upper Lee catchment Carrigadrohid Dam and Inishcarra Dam. Further information on these dams is included in Section 3.10. The Glengariff River and Dripsey River are the main rivers discharging to the reservoir along this reach.

Urbanised areas make up approximately 0.3% of the catchment with Macroom being the largest town. Other urban areas include Baile Bhuirne, Baile Mhic Ire, Béal Átha an Ghaorthaidh and Inse Geimhleach. The majority of the urban areas in the catchment are located along the primary watercourses.

3.2. Lower Lee catchment

The lower Lee catchment extends from downstream of Inishcarra Dam to Cork Harbour and covers an area of approximately 420km2. The catchment elevation varies from 367mAOD in the Boggeragh Mountains to approximately 5mAOD in Cork City and has an AAR value of 1100mm. The catchment has been broken down into fifteen sub catchments for detailed hydrological analysis as shown in Figure 3-3.

The catchment is drained by a number of watercourses, the main one being the River Lee, which flows primarily in an east west direction through a wide river valley from downstream of Inishcarra dam through Cork City where it discharges into Cork Harbour. Flows in the River Lee are partly controlled by the operations of Inishcarra Dam. There is also a number of tributaries discharging to the river along this reach. The tidal cycle in Cork Harbour also affects water levels in the River Lee in Cork City. The River Bride, Glasheen River and Curragheen River are the primary water courses draining the land to the south of the River Lee. The River Bride joins the River Lee upstream of Ballincollig with both the Curragheen and Glasheen Rivers discharging to the River Lee in Cork City. The Shournagh River is the primary watercourse draining the north of the catchment. The Shournagh River has two main tributaries; the Blarney River and the Owennagearagh River and joins the River Lee downstream of Ballincollig near Leemount Bridge.


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Figure 3-3 Lower Lee catchment broken down into fifteen subcatchments

The land in the lower Lee catchment is generally undulating with steeper sloping valleys located to the north of the catchment on the slopes of the Boggeragh Mountains. To the south of the catchment, both the River Lee and Bride River have wide flat floodplains which offer flood plain storage potential in a flood event. The geology of the catchment is predominantly sandstone till overlain by a cover of relatively fertile well drained acid brown earths. The geology and topography of the catchment results in a lower runoff potential than the upper Lee catchment as represented in Figures 6-3 and 6-5. The undulating nature and geology of the catchment ensures good agricultural land which is mainly used for pasture grazing. Arable land use is more prominent than in the upper Lee catchment with pockets of land used for complex cultivation on the outskirts of Cork City. Coniferous forestry is confined to the upper slopes of the Boggeragh Mountains with areas of transitional woodland scattered around the catchment.

Urban areas cover approximately 6% of the land in the catchment with Cork City extending for approximately 8km from the Waterworks Weir along the lower Lee valley to the mouth of the river. The suburban areas of Cork City make up a significant portion of the catchment of both the Glasheen River and Curragheen River. The high proportion of urban areas can lead to increased runoff in the sub catchments of these rivers. Runoff from a portion of the lands at

Lower Lee valley


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Cork Airport also discharges to the Glasheen River. Other urban areas located along the river valleys include Ballincollig, Blarney, Tower, Kilumney and Crookstown.

3.3. River Bride catchment

Figure 3-4 River Bride catchment broken down into three subcatchments

The River Bride catchment is located directly north of Cork City covering an area of approximately 42km2. The catchment has been broken down into three sub catchments for detailed hydrological analysis as shown in Figure 3-4.

The land varies in elevation from 188mAOD at Whitechurch in the north of the catchment to approximately 25mAOD along the River Bride valley in Blackpool. The AAR value for the catchment is 1070mm. A number of watercourses drain the catchment including the River Bride, Glennamought River, Glen River, and River Kiln. The upland areas of the River Bride and Glennamought River are made up of predominantly rural land which is used mainly for both pasture and arable farming. The low lying areas of the Glen and Kiln catchments are predominantly urban land and include the Cork City suburbs of Ballyvolane and Farranree. These urban areas have potential for a high runoff rate to the Bride, Glen and Kiln watercourses. Both the Glen River and River Kiln join the River Bride near Blackpool with the Glennamought River merging with the River Bride at the N20 intersection near Kilnap. The River Bride is culverted from Blackpool to where it discharges to the River Lee at the Christy Ring Bridge. The geology of the catchment is predominantly sandstone till overlain by a cover of relatively fertile well drained acid brown earths.

3.4. Glashaboy River catchment

The Glashaboy River catchment extends from the foothills of the Nagles Mountains to Cork Harbour at Dunkettle. The catchment covers an area of 145km2 and has been broken down into five sub catchments for detailed hydrological analysis as shown in Figure 3-5.


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Figure 3-5 Glashaboy River broken down into five subcatchments.

The Glashaboy River rises at the foothills of the Nagles Mountains and flows in a general north south direction to its confluence at Cork Harbour downstream of Glanmire. The river drains the west of the catchment with the Butterstown River draining the east of the catchment. The Butterstown River is a tributary of the Glashaboy River, joining the river at Riverstown. The Black Brook and Cloghnageshee River join the Glashaboy River in the north of the catchment. Water levels in the Glashaboy River are affected by the tidal cycle in Cork Harbour with the tidal influence extending upstream to the town of Glanmire.

The landscape of the catchment is characterised by undulating land which varies in height from 315mAOD in the northwest of the catchment to approximately 5mAOD at Dunkettle. The undulating landscape is intersected by the steep sided narrow valleys of the Glashaboy and Butterstown Rivers. Agriculture is the dominant land use in the catchment with a mixture of both pasture and arable land. Small pockets of transitional woodland are scattered around the catchment. Urban areas account for approximately 3% of the land cover in the catchment. The most significant urban areas include Glanmire and Sallybrook and both towns are located on the banks of both the Glashaboy and Butterstown Rivers. The moderately higher runoff potential suggested in

Glashaboy River valley near Glanmire


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Figure 3-6 Carrigtohill catchment broken down into 4 sub catchments

Figure 6-3 and 6-5 reflects both the topography of the catchment and the location of urban areas to the south of the catchment.

The geology of the catchment is predominantly sandstone till overlain by a cover of relatively fertile well drained acid brown earths. The annual average rainfall for the catchment is 1100mm.

3.5. Carrigtohill catchment

The Carrigtohill catchment is characterised by a series of small unnamed watercourses (typically 1-2m in width) which drain to Cork Harbour near Foaty Island and Harpers Island. The catchment is relatively small and covers an area of 22km2. The catchment has been broken down into four sub catchments for detailed hydrological analysis as shown in Figure 3-6.

The most westerly of these catchments is drained by a watercourse which rises in the north of the catchment and flows in a north south direction towards Carrigtohill. When the watercourse reaches a railway cutting to the north of Carrigtohill (Cork to Midleton railway line), the watercourse splits in two, with a portion of the flow siphoned across the railway cutting and

the remainder of the flow cascading down the railway cutting to a channel along side the railway. This channel discharges to Cork Harbour near Harpers Island. The siphoned water course continues southwards through Carrigtohill discharging to Slatty Pond upstream of Slatty Bridge. This watercourse has been engineered and landscaped both at the IDA Business and Technology Park and further south at the sewage treatment works. An agreement was reached between the IDA and Irish Rail on the flows through the siphon, however despite numerous enquiries regarding this agreement we have yet to receive information on the capacity of the siphon. The east of the catchment is drained by a number of small watercourses which converge to form a second channel which flows through Carrigtohill and discharges to Slatty Pond. Slatty Bridge is the tidal boundary between Cork Harbour and Slatty Pond. A number of flap valves at Slatty Bridge restrict the progression of high tides upstream into Slatty Pond.

The land to the south of the catchment is subject to significant development pressure. A large amount of development has been completed in the Carrigtohill area in the last number of years and a

Urban development in Carrigtohill


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considerable area of land is currently under development. Urban land use makes up approximately 6% of the catchment with Carrigtohill being the most significant urban area. Pasture and arable land makes up the remainder of the land use in the catchment with intertidal mudflats and wetlands around Slatty Water. The catchment soils consist of well drained minerals overlain on sandstone till. The topography of the watercourse draining the west of the catchment and the urban development at the downstream extent of the catchment are likely to lead to increases in the runoff potential of the catchment.

The AAR for the catchment is 1040mm, which drains to Cork Harbour from a maximum elevation of 155mAOD.

3.6. Owennacurra River catchment

The Owennacurra River catchment has two main rivers; the Owennacurra River and the Dungourney River. The catchment has a total area of 170km2 and is broken down into six subcatchments as shown in Figure 3-7. The annual average rainfall for the catchment is 1060mm.

Figure 3-7 Owennacurra catchment broken down into 6 subcatchments

The Owennacurra River rises in the northwest of the catchment and discharges to Cork Harbour south of the town of Midleton where water levels are influenced by the tidal cycle in Cork Harbour. The river predominantly drains the west of the catchment with Dungourney River draining the east of the catchment. The Dungourney River has its confluence with the Owennacurra River in Midleton and is the most significant tributary of the Owennacurra. Both rivers flow through undulating landscape with narrow river valleys in the upper catchment opening out to wide flat floodplains towards the town of Midleton. The ground levels vary in the catchment from 244mAOD in the northeast of the catchment to approximately 5mAOD at Cork Harbour. The steeper topography of the upper catchment and the presence of the urban


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area of Midleton to the south of the catchment results in a slightly higher runoff potential as shown in Figure 6-3 and 6-5.

The geology of the catchment primarily consists of a sandstone till subsoil overlain with a deep well drained mineral soil. Some alluvium deposits exist around the mouth of the river in Cork Harbour. The catchment characteristics and geology make the land ideal for agriculture with land used primarily for pasture and arable farming. Pockets of coniferous forest and transitional woodland are scattered around the catchment. The estuary of the Owenacurra River has areas of tidal mudflats and wetlands.

The town of Midleton is the largest urban area in the catchment and town is located on the confluence of the Owennacurra and Dungourney Rivers stretching southwards along the estuary. Ballynacurra is located on the estuary of the river to the south of Midleton.

3.7. Owenboy River catchment

The Owenboy River rises near Cross Barry and flows in a west east direction, discharging to Cork Harbour at Carrigaline. The lower reaches of the river are tidally influenced. The catchment drains an area of 129km2 and is broken down into ten sub catchments as shown in Figure 3-8. The AAR value for the catchment is 1160mm.

Figure 3-8 Owenboy River catchment broken down into ten subcatchments

The landscape of the catchment is characterised by undulating land which ranges in height from 200mAOD in the northwest of the catchment to approximately 5mAOD in Carrigaline. For the most part the Owenboy River flows through a wide open valley. The geology of the catchment is split along the Owenboy River. To the north of the river the geology primarily consists of sandstone tills overlain with deep well drained mineral soils. To the south of the river the geology primarily consists of shales and sandstone till overlain with deep, poorly drained mineral soils. Discussion on the runoff and flows for the Owenboy catchment are available in Section 6.2.2.The catchment topology and geological characteristic lends itself to


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Figure 3-9 Tramore River catchment broken down into 5 sub catchments.

agriculture. Pasture and arable land make up the majority of the land use in the catchment with some small pockets of natural vegetation and transitional woodland.

The main urban areas in the catchment are Ballinhassig and Carrigaline with urban areas accounting for 4% of the catchment. Carrigaline lies at the fluvial/tidal interface of the Owenboy River and Cork Harbour with Ballinhassig located further upstream in the Owenboy River valley. A significant portion of runoff from Cork airport, to the north of the catchment, discharges to the Owenboy River via the Liberty Stream and an outfall pipe.

3.8. Tramore River catchment

The Tramore River catchment covers an area of 21 km2 and lies to the south of Cork City with the suburban areas of the city making up a significant portion of the catchment land use. These suburban areas include Ballyphehane, Douglas, Grange and Donnybrook. The Tramore River rises in the southwest of the catchment and flows into Lough Mahon in Cork Harbour. The Tramore River is joined by a number of small tributaries draining the land to the south of the catchment with the most significant of these tributaries, the Douglas River,

joining it in Douglas. There are two discharge points from the northside of Cork Airport, which carry runoff from the airport to the Tramore River. The

catchment has been broken down into five subcatchments for detailed hydrological analysis as shown in Figure 3-9. The AAR value for the catchment is 1080mm.

Discontinuous urban fabric is concentrated in the north of the catchment and makes up 42% of the land use. Pasture and arable farmlands make up the remainder of the land use. Much of the urban fabric of the catchment has been constructed on made ground. The remaining catchment geology is primarily made up of sandstone till overlain with a well drained mineral soil. The proportion of urban land use results in the catchment having a higher than average runoff potential.

3.9. Cork Harbour catchment

The catchment of Cork Harbour is approximately 164km2 and consists of a relatively narrow band of land stretching around the perimeter of Cork Harbour. The catchment includes the areas of Great Island, Foaty Island and Little Island. Figure 3-10 shows a map of the Cork Harbour catchment. A number of urban areas are located around the shores of


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Cork Harbour and include the Cork City suburbs of Blackrock, Mahon, Douglas and Rochestown, which lie on Lough Mahon and the Douglas Estuary. Urban areas in the lower harbour include Passage West, Monkstown, Ringaskiddy and Crosshaven. The eastern shore of Cork Harbour is less densely populated and includes the villages of Whitegate and Aghada. Cobh is the largest town in the catchment and is located on the southern shore of Great Island. In total, urban land cover accounts for approximately 5% of the total.

Agriculture is the primary land use in the catchment with arable and pasture making up the majority of the land use. Intertidal mudflats are located along the shores of the harbour most notably in the upper harbour around Loch Mahon and in the river estuaries.

Figure 3-10 Cork Harbour catchment

The geology of the catchment primarily consists of a sandstone till overlain with a deep well drained mineral soil. A significant portion of the lands around the catchment rise steeply from the shores of the harbour to form an undulating landscape.

3.10. Operation of Carrigadrohid and Inishcarra hydroelectric dams

The River Lee hydro-electric scheme was built during the period 1952 to 1957 and consists of two dams at Inishcarra and Carrigadrohid. Inishcarra Dam is located approximately 13km west of Cork City with Carrigadrohid Dam a further 14km upstream. The construction of the dams created two lakes which stretch from Inishcarra upstream to the Gearagh. The lakes cover an area of approximately 14km2 and have a storage capacity of 45 million cubic meters. A number of meetings were held with ESB at Inishcarra to discuss the general operations of the dams and more specifically the operation of the dams during a flood event. At the time of writing this report we are still awaiting a significant portion of data to help inform our analysis


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of the operation of the dams. This data includes water levels from gauges within the reservoir as well as tail race and historical gate and spill settings for past flood events.

In normal day to day operations, the dams are run to maximise electricity generation that is dependant on the available head of water in the reservoirs and flow rate. Actual electricity generation varies with daily electricity demand. This demand has changed over the last number of years through the deregulation of the electricity supply in Ireland and the introduction of alternative energy sources. In the event of a flood the hydro power stations have priority on supply of electricity to the networks. This allows the stations to maximise the throughput of flood water through the turbines for optimum electricity generation and control of water levels in the reservoirs rather than just spilling through the sluice gates. Control of water levels in the reservoirs also varies seasonally. In the summer, water levels in the reservoir upstream at Carrigadrohid Dam are kept high to cover over tree stumps at the Gearagh. Drawdown of this reservoir is also limited to 0.6m in 24 hours so as not to impact on bank stability around the perimeter of the reservoir.

3.10.1. Operation of the dams in a flood event

During a flood event the dams are operated in line with the Regulations & Guidelines for the Control of the River Lee. These regulations were revised in 1991 following dam improvement works and again in 2003 to take account of the new hydro control centre based at Turlough Hill. Operations at the dams at Inishcarra and Carrigadrohid can be remotely controlled from the hydro control centre at Turlough Hill but local control is retained during a flood event. The regulations, which are currently under review, in conjunction with the dam improvement works, mean that the two dams are capable of dealing safely with flood events of up to a 0.01% annual exceedance probability. The regulations are applied when the water levels in the reservoirs reach the Maximum Normal Operating Level. Up to this level, the ESB Hydro Manager on the advice of the ESB Hydrometric Officer has the option of spilling to increase storage and/or reduce flooding at a later stage. The amount of spilling varies for each event and is based on water levels, meteorological forecasts and the judgement of the ESB hydro manager and hydrometric officer. The quantity of water spilled during a flood is based on detailed reservoir level and discharge operation rules at both dams. At all times during a flood event the top priority for the ESB is the proper management of the flood to avoid any risk to dam safety. Also of critical importance is that the peak outflow from Inishcarra does not exceed the peak inflow during a storm.

During a flood event the following information is available to the ESB at Inishcarra (it was noted by the ESB that some of these technologies have only been available in the last ten years);

ESB rain gauge data

The ESB have six rain gauges located around the catchment including gauges at both reservoirs, Inse Geimhleach, Reananerree, Ballyvourney and Mushera. Data from these gauges can be accessed via a dial in system. The gauges will also automatically inform both Inishcarra and Turlough Hill when a certain threshold of rainfall has been reached at the gauges. The system was due to be upgraded during December 2007. Data from the ESB rainfall gauges were not readily available for use in this study. However the coverage of Met Éireann rainfall gauges was considered sufficient for the purposes of this study.

Met Éireann forecast data


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Met Éireann issue detailed five day forecasts for the catchment to the ESB on a daily basis. Where rainfall is expected to exceed 25mm in any given day, Met Éireann will issue a flood warning to the ESB. Radar rainfall data is also available live to the ESB. This data is updated on a 15 minute interval basis and is accessed via computer software.

Flood model

An indicative computer flood model of the reservoirs allows the ESB to input a number of variables which in turn will provide information on how much water should be spilled from the reservoirs. These variables include the rainfall for the last 12 and 48 hours, the latest hourly rainfall values from the six ESB rain gauges, the latest reservoir levels and the predicted rainfall for the next five days from Met Éireann. The model produces inflow and discharge hydrographs from the inputted rainfall and reservoir level data.

Reservoir levels

Reservoir and tail race levels are available from a number of gauges in both the reservoirs and tail races and these levels can be accessed via mobile phones. Water levels at the two dams are also constantly on display at Inishcarra control station. Discussions with the ESB suggest that the operation of the dams is primarily based on reservoir levels prior to and during a flood event.

It is understood from the ESB that, during a flood event, inflows to the reservoirs from the ESB flow gauges in the catchment are not monitored (instead they use rainfall data and reservoir levels with their indicative flood model). Also, flows in the Shournagh River and Bride River are not monitored and spill rates from the Inishcarra dam during a flood event are not regulated based on flows in these rivers. Tide levels in Cork City are monitored by ESB staff during a flood event although it is understood that ESB operation rules do not include for the regulation of spill rates during a flood event based on tidal levels.


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4. Review and analysis of historic floods

4.1. Introduction

The recently released OPW National Flood Hazard Mapping website (http://www.floodmaps.ie/) has provided a wealth of information about past flood events in the Lee Catchment. It contains information on past flood events from detailed reports and photographs, to newspaper articles and minutes of meetings. The following sections provide a summary of the historic flood information that was reviewed. The information in this section is based on the reports available from the Flood Hazard Mapping website, many of which were obtained from Cork City and Council area engineers as well as specific studies undertaken after larger events, such as August 1986. The list of flood events noted here has been further enhanced from the public consultation phase of the project and through discussion with Local Authority Area Engineers.

4.2. Flood events

The review of documents has highlighted that there are a number of areas at risk of flooding within the Lee catchment. It is apparent that there are several rural and urban areas that experience frequent flooding including Cork City, Ballincollig, Macroom and Carrigaline among others. These frequent flooding problems can cause flood risk to public roads, properties and farmland and result from both fluvial and tidal mechanisms. The main events that have occurred in the Lee include the August 1986 flood event which caused severe flooding in Macroom in particular and the November 2004 tidal event which caused flooding in Cork City and communities around the harbour.

Appendix B contains a more detailed list of the flood events and areas flooded as collated during the review of historic floods in the Lee catchment.

4.3. Summary of flood mechanisms

From the reports and documents reviewed in Section 4.2, risk of flooding occurs from both fluvial and tidal mechanisms. A further problem occurs from pluvial flooding in some areas where surface water cannot escape due to high river or tide levels. Flooding is also exacerbated by under capacity bridges and culverts and by debris causing blockages in some areas. For example bridge under capacity/blockage issues in Crookstown, Ballymakeery, Carrigaline and Douglas (pedestrian bridge since up-graded on Ballybrack Stream after 2002 flooding) have caused localised flooding problems in those areas, Appendix B contains further information on flood mechanisms during historic floods in the Lee catchment.

Table 4-1 lists the worst recent fluvial and tidal flood events documented in terms of both volume of flooding and number of areas flooded.


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Table 4-1: Significant recent events in the Lee Catchment

Flood Event Main Flood

Mechanism

Rivers Affected Areas Affected

August 1986 Fluvial Lee; Sullane; Laney; Shournagh

Baile Mhic Íre; Macroom; Ballincollig; Blarney; Cork City

November 2000 Fluvial Lee; Owennacurra; Martin; Shournagh

Midleton; Watergrasshill; Fivemilebridge; Ballinhassig; Ballygarvan; Cork City; Ballincollig; Blarney

November 2002 Fluvial Lee; Glashaboy; Owenboy; Ballybrack; Butlerstown

Douglas; Carrigaline; Ballygarvan; Ballinhassig; Monkstown-Passage West; Riverstown

October 2004 Tidal Lower Lee and Cork Harbour

Cork City; Cobh; Whitegate; Monkstown-Passage West; Crosshaven; Ringaskiddy; Glounthaune; Glanmire; Midleton; Carrigaline

December 2006 Fluvial Sullane Baile Mhic Íre

Figure 4-1 illustrates the seasonality of the flood history in the Lee Catchment (fluvial & tidal). The majority of the floods have occurred during the winter season, most in November. However, one of the worst fluvial floods occurred in early August (classed as Autumn).

Summer 0%Spring19%

Autumn19%

Winter62%

Figure 4-1 Seasonality of historic tidal and fluvial floods in the Lee catchment


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Since the Lee CFRAMS commenced in August 2006 and up to the end of January 2008, there have been four relatively minor flood events in the catchment:

• On 8 October 2006 during a period of exceptionally high tides (return period of approximately 18 years) a number of roads and properties in the Cork City centre area were flooded. Particular problems were caused by cars driving through the flooded streets and causing surface waves, which further increased the flood damage to properties.

• On 25 October 2006 a flood event occurred due to very heavy rain in the county area of Cork, particularly around the harbour.

• On 7 and 9 December 2006, flooding (with a return period of between 2 and 5 years) occurred in Baile Mhic Íre following a number of days of heavy rainfall. The general consensus was that the flooding on the 9 December was worse than the flooding that took place in the village in 2001 but not as bad as the flooding of 1986. During the December 2006 event, areas downstream of Inishcarra Dam including Inishcarra and Carrigrohane Road were also flooded.

• Following a number of days of rain, flooding occurred at a number of locations around the catchment on 09 January 2008 including the Lee Road, Lee Fields and parts of Macroom. The flooding was not as extensive as December 2006, however, according to local residents water levels in the Shournagh River and Dripsey River were the highest for over 8 years.

4.4. Selection of calibration events

Based on the review of flood events and associated information a selection of possible calibration and verification events have been chosen, as shown in Table 4-2. The use of the events is subject to sufficient information, in terms of both flow gauge data and documented evidence of areas and levels of flooding. The use of more recent events is preferred and to support this approach four of the events selected were within the last seven years. As can be seen from Table 4-2, a total of six events have been identified covering both fluvial and tidal flooding mechanisms. Of these six events at least two are available for each of the upper Lee, lower Lee, Glashaboy, Owennacurra and Owenboy river models allowing for a calibration and verification event for each of those models.

Table 4-2 Possible calibration/verification events for the Lee and tributaries

River Model Dec 1978 (Fluvial)

Aug 1986 (Fluvial)

Nov 2000 (Fluvial)

Nov 2002 (Fluvial)

Oct 2004

(Tidal)

Dec 2006 (Fluvial)

Upper Lee x x x

Lower Lee x x x

Glashaboy x x

Owennacurra x x

Owenboy x x


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In addition to the five hydraulic river models noted in Table 4-2, three hydraulic models representing the Tramore River, Bride River and the watercourses that flow through Carrigtohill are also to be constructed. These watercourses are ungauged and therefore there is no calibration information available for these models. However, information on any flooding having occurred in these areas will be considered when modelling these watercourses with design events. Further details on the calibration events and hydrology are contained in Section 6.4.

4.5. Coverage of meteorological and hydrometric gauges

4.5.1. Overview

This section of the report presents recommendations for enhancing the meteorological and hydrometric network in the Lee catchment for the purposes of improving flood flow estimation.

The Lee CFRAMS study area has an abundance of meteorological and hydrometric gauges, however not all gauges are ideally located to aid flood estimation, have data readily available or have sufficient accuracy.

4.5.2. Meteorological gtauges

Met Éireann and OPW have established a comprehensive network of meteorological gauges in the Lee CFRAMS study area. The development of isohyetal plots would be enhanced by three additional meteorological gauges in the East and South of the study area (Figure 4-2).

Two additional rainfall gauges are recommended in the Owenacurra catchment, one at the base of the valley 1km North of Middleton, and another on a high spur between the Owenncurra and Leamlarra Rivers.

Figure 4-2 Recommended locations for additional meteorological and hydrometric gauges


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As identified in Section 6, further monitoring of the Owenboy catchment is warranted, and a meteorological gauge at the base of the Owenboy valley in the vicinity of Ballinhassig would assist in identifying likely topographical trends in rainfall patterns.

4.5.3. Hydrometric gauges

A reasonable hydrometric gauge coverage exists of the primary rivers, with the exception of the Tramore River, Curragheen River, Glasheen River, Bride River North and Dungourney River. Gauges on all five rivers would assist in the flood estimation of sensitive watercourses, and are recommended. Section 6.2.2 recommends that an additional hydrometric gauge is placed on the Owenboy River to assist in future reviews of the catchment runoff characteristics. Figure 4-2 provides indicative proposed locations for the four recorders, subject to a site specific suitability review.

Of the 583 cumulative years (to 2006) of hydrometric data available in the study area, 295 years are held in undigitised paper chart format, although much of this paper record has had annual maximum flows manually extracted for this study. Much of the ESB paper chart record is not readily available for third party use. It is recommended that the full data record is digitized to enable further analysis options to future reviews of the Lee CFRAMS hydrology, including peak over threshold statistical analysis and unit hydrograph analysis.

Difficulties appear to exist in accessing ESB digital data between 2002 and 2006, and in particular reservoir levels and gate and spill flows between 2000 and 2006 are not readily available. It is recommended that a joint ESB and OPW review is undertaken to ascertain whether further collaboration is possible in accessing, storing and disseminating data from ESB gauges.

Rating reviews were undertaken of eleven prioritised gauges as part of this study. Rating reviews of the remaining ten gauges as part of the next review will assist in maximizing the potential of the lower priority hydrometric gauges in the study area.


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5. Meteorology

5.1. Overview

The meteorological analysis undertaken for the Lee CFRAMS follows the Flood Studies Report (FSR) Volume II Meteorological Studies approach. The FSR is the current industry standard for flooding studies in Ireland and hence the definitive baseline for any subsequent review of extreme patterns. The UK Flood Estimation Handbook Volume 2 was also referred to, particularly in the treatment of the median annual rainfall as opposed to the mean annual rainfall.

In accordance with the FSR, the following primary meteorological outputs were produced:

• Average Annual Rainfall isohyetal plots for Lee Catchment;

• M5-2day (5 year return period rainfall, with a 2 day storm duration ) isohyetal plots for the Lee catchment;

• Rainfall growth curves for the Lee catchment;

• Values for Jenkinson’s r (M5-60min/M5-2day).

The methodology undertaken is presented in detail in Appendix C and further background information on the methodology used can also be obtained from:

• Flood Studies Report Volume II Meteorological Studies Section 2 : Regional Analysis

of Point Rainfall Extremes and Section 3 : Estimation and Mapping of M5 (5 year)

Values for Different Durations;

• Flood Estimation Handbook Volume 2: Rainfall Frequency Estimation (FEH) Chapter

8: Deriving Growth Curves.

The following sections summarise the primary outputs from the meteorological analysis.

5.2. Rainfall growth curves

Extreme rainfall analysis in catchment flooding studies is concerned with defining the:

• Spatial distribution of an index event (FSR uses the 5 year return period rainfall);

• Relationship between the index event return period and alternative return periods (referred to as the growth curve);

• Relationship between different storm durations.

The Lee CFRAMS rainfall growth curve was developed from available rainfall records, and then compared to the FSR rainfall growth curves. Data from 42 meteorological stations were available to this study and 29 stations were considered to have a sufficient length of record for extreme rainfall statistical analysis (greater than 10 years of data) (Table 5-1). Rainfall records were provided by Met Éireann up to 30 June 2006. Data availability at rainfall gauges and data type is outlined in Appendix A4.


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Table 5-1 Meteorological Station Records to June 2006

Station Name Station ID N

(yrs)

AAR

(mm)

M5-2Day

(mm)

Roche's Point 1004 54 983 68.9

Rathduff G.S. 1504 60 1119 80.8

Coomclogh Daily 1901 13 2091 103.3

Ballyvourney (Clountycarty) 2604 58 1433 88.3

Gouganebarra Daily 2704 58 2391 137.2

Donoughmore Daily 2804 58 1196 81.3

Ballinagree (Mushera)* 2904 56

Ballingeary (Voc.Sch.) 3004 58 1841 122.4

Carrigadrohid (Gen.Stn.) 3604 53 1102 78.4

Inishcarra (Gen.Stn.) 3704 52 1022 75.2

Macroom (Renanirree) 3804 47 1517 95.0

Youghal (St.Raphael's 3806 43 889 68.7

Cork Airport 3904 44 1123 82.7

Ballineen Daily 4002 21 1276 88.0

Ballintrideen Daily 4402 11 1182 84.8

Ballymacoda (Mountcotton) 4404 30 940 70.7

Ballineen (Carbery) 4602 11 1467 85.6

Dungourney (Ballyeightragh) 4804 28 1229 84.7

Killeagh (Monabraher) 4904 30 1151 93.2

Shanagarry North 5004 30 938 66.1

Macroom (Curraleigh) 5204 29 1778 91.1

Dunmanway (Keelaraheen) 5302 6

Cork Montenotte 5404 22 953 77.3

Cork (Douglas) 5504 22 1076 84.8

Aherlamore Daily 5704 21 1203 85.3

Watergrasshill (Tinageragh) 5804 18 1181 88.4

Muskerry (Golf 6104 11 1087 84.8

*Gauge reported as unreliable after 1969


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In accordance with FSR methodology, the 29 rainfall gauges were separated into 3 subsets: M5-2Day range 60-75mm, M5-2Day 75-100mm, M5-2Day range 100-150mm. Results from the quartile analysis were plotted against the FSR rainfall growth curves for England/Wales and Scotland/Northern Ireland as Ireland rainfall growth curves were not provided in the Flood Studies Report. Common practice in Ireland is to adopt England/Wales values for the Dublin Region, and Scotland/NI values for the remainder of Ireland.

Comparing plotted study values against the standard FSR rainfall values, suggest that the Lee catchment rainfall patterns closely follow the milder Scotland/Northern Ireland growth curve for all three range classes. A flattening trend is apparent in the H1 (highest value) data in Figure 5.2 and 5.3, which may be indicative of a spatial dependence influence in the high end value. Based on the closeness of fit, the possibility of spatial dependence influences in the H1 data and the requirement to consider return periods outside of the range supported by the statistical record, the Scotland/Northern Ireland rainfall growth curves have been used directly in the Lee CFRAMS analysis (Figures 5-1 to 5-3). A further explanation of the quartile analysis is provided in Appendix C.

River Lee Catchment 60-75mm 2 Day Growth Curve

1/2 1 2 10 20 50 100 1000 1000050

50

100

150

200

250

300

-2 0 2 4 6 8 10

reduced variate y

Ra

infa

ll (m

m)

Eng/Wales Scot/NI Lee - Quartile Lee - H1

Ret urn Per iod

Figure 5-1 Lee quartile analysis compared to FSR England/Wales and Scotland/ Northern Ireland growth curves (for gauges with a M5-2Day range of 60-75mm)


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River Lee Catchment 75-100 mm 2 Day Growth Curve

1/2 1 2 10 20 50 100 1000 1000050

50

100

150

200

250

300

-2 0 2 4 6 8 10

reduced variate y

Rai

nfal

l (m

m)


Ret urn Period

Figure 5-2 Lee quartile analysis compared to FSR England/Wales and Scotland/ Northern Ireland growth curves (for gauges with a M5-2Day range of 75mm-100mm)

Lee Catchment 100-150 mm 2 Day Growth Curve

1/2 1 2 10 20 50 100 1000 1000050

50

100

150

200

250

300

350

-2 0 2 4 6 8 10

reduced variate y

Rai

nfal

l (m

m)


Ret urn Period

Figure 5-3 Lee quartile analysis compared to FSR England/Wales and Scotland/ Northern Ireland growth curves (for gauges with a M5-2Day range of 100 – 150mm)


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5.3. Spatial distribution of extreme rainfall

The spatial distribution of extreme rainfall patterns are often derived by plotting the index rainfall event across the area of interest. In accordance with the FSR, two index rainfall distributions were used in this study, the M5-2Day (5 year return period, 2 day duration) and the Jenkinson’s Ratio (5 year 1hr duration divided by 5 year 2 day duration). The former defines the distribution of the rainfall magnitude, with the 2 day duration facilitating the use of the more abundant daily rainfall gauges (29 used in Lee CFRAMS including synoptic stations), while the latter defines any spatial variation in the relationship between alternative rainfall durations, from sparser synoptic stations (2 used in Lee-CFRAMS).

M5-2Day values from available meteorological stations were plotted and rainfall isohyetal contours developed. Contours were manually drawn to facilitate the inclusion of a topographical bias, as apparent in the available data. The M5-2Day contours were found to vary from 125mm in the western mountains to 70mm in the south east (Figure 5-4).

The contours displayed a very good correlation in the western quarter of the study area with the original FSR M5-2Day plots, however, the FSR plots are found to under predict actual rainfall patterns by 7% to 20% from around Inse Geimhleach, to the eastern extent of the study area. This under prediction has important implications for flood alleviation, hydraulic structure and surface water drainage design throughout the study area (Figure 5-4).

The study M5-2Day distribution does however correspond well with preliminary outputs from the ongoing Flood Studies Update (FSU) (Figure 5-5), with little discernable variance throughout the study area. Minor variance exists in the far western mountains (Carran, Conigar, Foilastooken), with the FSU reaching 150mm. This variance is potentially through the use of additional rainfall gauges outside of the study area by the FSU, however the overlap with the study catchment area is negligible, and the variance is of little consequence to flood estimation in the Lee catchment.

Given the rainfall under prediction identified in the FSR rainfall mapping, it is recommended that the City and County Councils consider the interim use of the Lee CFRAMS M5-2Day contours or preliminary FSU outputs for surface water drainage design within the study area or increase FSR M5-2Day values by 20% throughout the Lee CFRAM study area. Following dissemination of FSU rainfall information, it is recommended that the FSU rainfall is used directly for all design applications.


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Figure 5-4 M5-2Day. Lee-CFRAMS compared with FSR

Figure 5-5 M5-2Day. Lee-CFRAMS compared with preliminary FSU (based on meteorological data to June 2006)

Development of study specific Jenkinson’s ratio contours is limited, as long term hourly rainfall data is only available at Roche’s Point and Cork Airport synoptic stations in the southeast of the study area. No significant deviation is discernable between the FSR, preliminary FSU results and the values derived as part of this study (Figure 5-6).


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As no spatial distribution across the study area is possible from the Roche’s Point and Cork Airport stations, the preliminary FSU contours have been used in this study.

Figure 5-6 Jenkinson’s Ratio. Lee-CFRAMS and preliminary FSU (based on meteorological data to June 2006)

Figure 5-7 AAR values for the Lee catchment (based on meteorological data to June 2006)


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5.4. Historical climate change

A review of historical rainfall annual maximum, suggests that extreme rainfall may be slightly tending above the historical median (Figure 5-8). While the 2005 5 year moving average was at the historical median, the 2005 10 year moving average is 8% above the historical level. The 1 year average median for 2005 is 23% above the historical level, and anecdotal evidence of flooding in 2006, suggests that subsequent long term averages may tend higher. However, an insufficient trend is apparent from the historical Lee catchment rainfall data to suggest a sustained departure from historical fluctuations.

Based on the high 10 year average level, it is recommended that the Lee CFRAMS annual maximum rainfall values are reviewed on an annual basis. If this review identifies a sustained increase in long term annual maximum rainfall trends, it is recommended that the index rainfall is increased throughout the study area.

0.5

1.0

1.5

2.0

1945 1955 1965 1975 1985 1995 2005

Hydrometric Year

Ran

nual

Max

/Rav

erag

e an

nual

Max

10 year average 5 year average

Figure 5-8 Temporal changes in annual maximum rainfall


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6. Hydrology

The following chapter details the hydrological process undertaken to derive the calibration and design event hydrology. The analysis is focused on maximising the potential accuracy of design flow estimates that will in-turn be used for subsequent hydraulic modelling, flood mapping and flood management option developments. The methodology is summarised as follows:

1. A rating review was undertaken by the project team to build on the ‘low confidence’ associated with the gauging stations (March 2006) and flow data re-generated from the hydrometric level record (Section 6.1);.

2. The index flood of individual hydrometric gauges is calculated from the re-generated flow record. This estimate is said to be for a gauged catchment. In this study the Median Annual Flood (Qmed) is used as the index flood, consistent with the Flood Estimation Handbook (Section 6.2.2);

3. The Flood Studies Report Unit Hydrograph technique is used to estimate the index flood at the gauged catchments and then adjusted to the estimate predicted from the flow record by scaling a runoff parameter, SPR (Section 6.2.3);

4. The index flood for ungauged catchments is calculated using the Flood Studies Report Unit Hydrograph technique and an averaged SPR scale parameter from nearby gauged catchments applied (Section 6.2.3). This technique ensures that all flood estimates are correlated to actual flow records;

5. The relationship between the index flood, Qmed and other more extreme floods is defined by the growth curve. This study has used the Flood Estimation Handbook statistical techniques to derive a study growth curve from flow records (Section 6.3);

6. Calibration events for the hydraulic models have been selected, and Section 6.4 defines the sources of the flow inputs;

7. Design hydrographs were developed using the Flood Studies Report techniques, applying the study growth curve and a study derived unit hydrograph (Section 6.5). The design hydrographs form the primary deliverables from the hydrological analysis.

6.1. Rating curve review

Rating curves provide a relationship between water levels and flows in a river, which can be defined at any location along a river reach. Gauging stations record the water level at a particular location along a river reach and the rating curve is used to produce a flow estimate from these recorded water levels. The rating curve is established through recorded field measurements of flow against a recorded water level for a range of water levels, known as spot gaugings. Extrapolation of the rating curve is often necessary as spot gaugings tend not to cover the full range of levels at a gauging station. For example, during high river flows spot gaugings are difficult to record due to flood conditions and the fact that gauging structures are often drowned.

As part of the inception process, the high flow rating for each gauge in the catchment were assessed based on information received from the EPA, OPW, ESB and the Hydro-logic report “Review of Flood Flow Ratings for Flood Studies Update” (March 2006). Based on the


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information available, all gauges in the catchment were assigned a low confidence level for out of bank high flows. Eleven hydrometric gauges were selected for a detailed rating review based on meaningful data records and providing a good spatial coverage. Table 6-1 provides details of the gauges reviewed, gauge location, type of gauging and the DTM data used to develop the hydraulic models. Figure 6-1 shows the location of the eleven gauges.

Table 6-1 Details of the gauging stations used in the rating curve review

Gauging station Location Managing

Organisation

Gauging type DTM data

19001 Ballea Bridge OPW Weir LiDAR

19006 Glanmire EPA Open channel HRSC

19011 Leemount Upper ESB Open channel HRSC

19012 Leemount Lower ESB Open channel HRSC

19013 Inishcarra ESB Open channel HRSC

19014 Dromcarra ESB Open channel LiDAR

19015 Healy’s Bridge ESB Open channel HRSC

19016 Ovens ESB Open channel LiDAR

19018 Tower EPA Open channel HRSC

19020 Ballyedmond EPA Open channel LiDAR

19031 Macroom ESB Open channel LiDAR


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Figure 6-1 Location of the 11 gauges for the rating curve review

A site visit was carried out to each of the individual gauges to help understand the hydraulics and any relevant features at the gauges. A review of available historical information on the gaugings was carried out to assess if the gauging station had changed with time. This included assessment of any structural changes or changes in the channel upstream and downstream of the gauge. This information was used in developing a channel and structure cross section location plan to ensure the hydraulic model reaches extend far enough to explicitly model any impacts upstream and downstream of the gauges.

The rating curve review assessed the existing rating and extended the rating curves to high flows using local hydraulic computer models and followed guidance in the “Extension of Rating Curves at Gauging Stations. Best Practice Guidance Manual. R&D Manual W6-061/M” (2003). Eleven separate ISIS 1D hydraulic computer models were developed using a combination of channel & structure cross sectional survey data and DTM’s developed from either LiDAR or HRSC data. Cross sections were surveyed at approximately 100m intervals and extended over-bank for 20 metres to allow for tie in to the floodplain DTM. Up to four cross sections were surveyed at structures and were sufficiently detailed to allow accurate representation of the structure in the hydraulic models. The DTM was used to develop both integrated channel/floodplain cross sections and ISIS reservoirs. Where appropriate, ISIS reservoirs are used in place of extended floodplain cross sections to model floodplain storage by ensuring that overbank spills from a channel are accounted for and may drain back to the channel as the flood subsides. The models were run with flow hydrographs and a normal depth downstream boundary.

The models were calibrated using in bank spot gauge data. Water levels obtained from the hydraulic models were used to assess the existing rating and to generate the over bank section of the rating curve. Sensitivity analysis was carried out to assess the effect on the predicted rating of changes to specific hydraulic parameters such as channel roughness and structure coefficients.

An analysis spreadsheet was set up for each of the individual gauges to carry out the rating review. The current rating equation data was used to plot the rating curves at each of the


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eleven gauges. Spot gauge data was plotted for both the entire data range and the winter data range and checked for any onerous values.

Water level data and flows were exported from ISIS to the analysis spreadsheet. Data was exported for various hydraulic model runs using specific hydraulic model parameters. Water level data was converted to a staff gauge datum to allow the results to be plotted against the existing rating curves. A revised rating was established by adjusting the number of rating equation segments and values until the desired rating curve was achieved. Where there was uncertainty regarding the rating, the relevant authority was contacted for further information on the rating values being used. Figure 6-2 and Table 6-2 show the revised rating for gauge 19020 at Ballyedmond on the Owennacurra River. Further information on each of the individual rating curves is available in Appendix D1.

G19020 at Ballyedmond

0.0

0.5

1.0

1.5

2.0

2.5

0 10 20 30 40 50

Flow (m³/s)

Sta

ge (

m)

spot gaugings w inter spot gaugings Halcrow recommendedn=0.040 n=0.050 EPA Ratingn=0.035 n=0.045 (Best f it)

Bankfull stage:1.5m ASD

Figure 6-2 Revised rating curve for gauge 19020


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Table 6-2 Revised rating equation values for gauge 19020. Flow Q is calculated using the equation Q(h)=C*(h+a)^b. The parameters for the equation are obtained from the table below for varying stages in water depth h.

Section Minimum

stage (m)

Maximum

stage (m)

C a b

1 0.000 0.374 28.986 0.000 3.428

2 0.374 0.895 10.011 0.000 2.347

3 0.895 1.417 9.530 0.000 1.901

4 1.417 2.000 9.564 0.000 1.931

5 2.000 2.500 9.217 0.000 1.995

6.2. Index flood

6.2.1. Median annual maximum flood Qmed

The hydrological analysis approach is similar to that used in the rainfall analysis (Section 5), and is concerned with identifying the spatial distribution of a low return period flood (index flood) and the relationship between the index flood and floods of other magnitudes (growth curve).

The Average Annual Maximum Flood (Qbar) has typically been used as the index flood in Ireland, in accordance with the FSR. However, hydrological practitioners now have a strong preference for using the Median Annual Flood (Qmed) in place of Qbar, as the estimate is not as susceptible to the inclusion or omission of isolated extreme flood events. The Qmed estimate is therefore potentially more accurate from shorter data records than Qbar. The UK FEH adopts Qmed as the standard index flood.

Qmed is defined as the flood that is expected to occur or be exceeded, on average, every other year.. In statistical terms the flood is said to occur or be exceeded on average once every two years and have a 50% probability of annual exceedance.

For the Lee CFRAMS, all Qmed estimates are either derived directly from hydrometric station records (gauged catchments), or inferred from nearby hydrometric station records to catchments without hydrometric records (ungauged catchments).

6.2.2. Gauged catchments

The FEH (Vol 3 Section 2.2) recommends that annual maximum records greater than 14 years be used for Qmed estimation, below which peak over threshold records should be used.

Much of the Lee catchment hydrometric record available is as annual maximum floods manually derived from chart records. Peak over threshold (POT) data is limited to gauges with continuous data records, often comprising of five years record. Based on data availability, this study has slightly deviated from FEH guidelines and derived gauged Qmed


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estimates from all hydrometric records exceeding 10 years and accounted for increased uncertainty from records less than 14 years in the confidence limit analysis presented in Section 6.2.4.

Hydrometric data records were manually reviewed for data gaps and consistency to nearby gauges. Where gaps existed, all nearby hydrometric records were reviewed to ascertain whether the gap may have missed the annual maximum event. Where the gap was deemed to be inconsequential the gauge hydrological year was accepted as valid. If the gap was deemed to potentially contain an annual maximum event, the gauge hydrological year data was omitted from the analysis. An audit trail was maintained of data omitted and the rationale.

Qmed was found to vary between 17.5m3/s on the smaller Owenboy catchment (Gauge 19001) and 218m3/s on the Lee downstream of the Inishcarra hydroelectric dam (Gauge 19013) (Table 6-3). The FSR suggests that the index flood tends to a non-linear relationship with catchment area, and regression analysis suggested that Qbar can be proportional to A0.77 (where A equals catchment area). Figure 6-3 illustrates the Lee Qmed values indexed to A0.77/10, within the context of measured Qmed throughout the greater southwest region. A visual comparison suggests that many of the Lee Qmed records are consistent with the runoff trends observed throughout the region (broadly 8-23), with the exception of the Owenboy 19001 gauge, where the Qmed would appear to be half of the anticipated flow in relation to other records. Furthermore, Section 6.2.3 suggests that the runoff parameters calibrated to the gauge are 50% of the FSR catchment characteristic values for the catchment.

No apparent explanation is available for the lower Qmed values for the gauge at 19001:

• A rating review was undertaken of the gauge as part of this study, suggesting that the level-flow relationship is appropriate;

• Review of historical flood levels recorded at the gauge suggest that it should not be unduly influenced by the upstream arch bridge or flows bypassing on the low road on the left bank;

• Detailed EPA/Teagasc soil maps do not suggest lower runoff parameters within the Owenboy catchment in relation to other Lee catchments;

• Calibration of the hydraulic model and flood mapping from design flows suggest that the flows represent historical anecdotal evidence of flooding. It is interesting to note that Cork County Council staff have indicated that preliminary 1 in 10 year flood extent mapping may over estimate flooding at Ballygarvan, suggesting that the flow records are not unduly low. Also, the growth curve derived from the gauged record is both consistent with the average study growth and the standard FSR Ireland growth curve.

This report acknowledges that an unresolved apparent discrepancy may exist at the 19001 gauge; however the hydrometric record remains the most accurate depiction of runoff at the location. It is recommended that the OPW consider the installation of a temporary recorder nearby on the Owenboy to facilitate confirmation of recorded flood flows in subsequent revisions of the Lee CFRAMS.


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Figure 6-3 Regional Qmed Relationship (77.0

10

A

Qmed)


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Table 6-3 Gauged Qmed

Station

Reference

Watercourse Gauge Qmed

(m3/s)

Record Length

(yr)

19001 Owenboy Ballea 17.4 31

19006 Glashaboy Glanmire 37.7 16

19011 Lee Upper Leemount

208.6 55

19012 Lee Lower Leemount

185.3 38

19013 Lee Inniscarra 218.5 61

19014 Lee Dromcarra 71.8 20

19015 Shournagh Healy's Bridge 70.5 28

19016 Bride Owens 29.5 8

19018 Shournagh Tower 70.2 20

19020 Owennacurra Ballyedmond 22.5 23

19031 Sullane Macroom 141.7 11

6.2.3. Ungauged catchments

Estimates of the index flood for ungauged catchments are derived using the FEH donor catchment approach in conjunction with the FSR unit hydrograph method. The FEH donor catchment method is based on scaling runoff parameters at gauged catchments to match statistically derived flow and then inferring the proportion of scaling used to ungauged catchments. Regional scaling of FSR derived ungauged catchments was also recommended prior to the FEH, as discussed in Cunnane and Lynn 1975 (Section 5.5). By calibrating the scale parameters at gauged catchments, the method ensures that all flow estimates are either directly obtained from actual flood records or inferred from flood records. Figure 6-4 illustrates the donor catchment methodology used and Section 6.5.3 and Appendix D provide further explanation of the FSR unit hydrograph method.

Figure 6-5 outlines the gauged and ungauged catchments and SPR scale parameters derived in this study. SPR scale parameters follow a spatial trend with catchments to the north of the River Lee experiencing 7%-50% greater runoff characteristics than that suggested by the FSR catchment characteristics method. Conversely, catchments to the south of the River Lee experience a 12%-50% reduction in runoff characteristics.


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Figure 6-4 Ungauged catchment methodology

Develop Unit Hydrograph

Boundary

SPR and Tp values from

Catchment

Characteristics

Develop Unit Hydrograph

Boundary

Use calibrated scale factors to

scale SPR and Tp

Design flow calibrated to

gauged catchment

Gauged Catchment Ungauged Catchment

Design flow equals

statistical flow

Scale SPR and Tp

SPR and Tp values from

Catchment

Characteristics


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Figure 6-5 Applied catchment SPR scale factors for the study


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6.2.4. Qmed confidence limits

Alternative Qmed confidence limit methods are used, depending on if the estimate is based on a gauged record, or if it is an ungauged catchment.

The confidence levels of Qmed estimates from gauged records are directly linked to the length of the gauged record and the degree of variation within the record. These confidence limits have been calculated directly using the methodology outlined in the FEH.

However, the confidence levels of ungauged Qmed estimates are difficult to define. Based on the FEH donor catchment method used the confidence would be linked to:

• Accuracy of the inferred gauge record;

• Relative spatial accuracy of the catchment characteristics;

• Accuracy of the rainfall-runoff model used.

As the method is effectively calibrated to gauged records, inaccuracies from the rainfall-runoff model should be minimised, thereby suggesting that dominant uncertainties are from the underlying gauged record and the relative catchment characteristic accuracy.

The derivation of study specific rainfall characteristics from a dense rain gauge network suggests that the rainfall inputs (M5-2Day, AAR and Jenkinson’s ratio) are high. However the FSR Ireland Winter Rain Acceptance Potential mapping offers only a broad depiction of regional soil parameters. In comparison to the recently released Teagasc/EPA soil maps, the FSR mapping suggests a much lower spatial variability in drainage potential across the study area. The FSR mapping does identify some isolated areas of high runoff potential not identified in the Teagasc/EPA mapping, suggesting that the FSR mapping may have identified some additional visible land features.

Ungauged Qmed confidence limits have been estimated based on the spatial variability in the SPR scale factor:

• The SPR scale factor is determined for a gauged catchment;

• The SPR scale factor is then recalculated for the gauged catchment as if the gauged record was not present;

• The ratio of the flows between the two methods offer an estimate of the possible errors that might be inherent for an ungauged estimate in the vicinity of the gauged catchment.

This method apportions a greater level of uncertainty to areas of high spatial variability. Not surprisingly, the catchments in the vicinity of the greatest and lowest scale parameters exhibited the greatest variability, with the Sullane, Upper Lee and Owenboy catchments having an error of 45%, 44% and 39% respectively from their gauged Qmed estimate. The spatial uncertainty attributable to the Owenboy catchment does not become apparent in the analysis due to the low weighting provided to this gauge to ungauged catchment estimates outside of the Owenboy catchment. The low weighting was due to uncertainty in the representativeness of the catchment to other catchments in the study area. Conversely areas of low spatial variability in the northern and eastern extent of the study area, the Bride, Owenacurra and Glashaboy were found to have very low errors of 6%, 3% and 6% respectively.


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Ungauged catchment confidence limits were then determined by adding the confidence level from the inferred donor catchment(s).

Figure 6-6 Study Qmed 95 percentile confidence limits


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Figure 6-6 compiles gauged and ungauged Qmed 95%ile confidence limits for each catchment. Based on these values the average study wide catchment area upper 95%ile confidence limit for Qmed is 1.41. Section 6.5.4 presents recommended design flow confidence limits and Section 8.6 discusses the use of confidence limits in the Lee CFRAMS.

6.3. Pooled hydrology growth curve

6.3.1. Growth curve rationale

Various debate has been held in Ireland as to the appropriateness of the FSR Ireland Growth Curve. Bruen et al 2005 suggest that the Flood Studies Report significantly underpredicts extreme flows in the Dublin and Mid Eastern Region, yet Cawley et al 2003 suggest that the FSR Ireland growth curve overpredicts extreme flows for all regions, including the East of Ireland.

Based on current uncertainty in the FSR Ireland growth curve, a statistical analysis of flow records in the Lee has been undertaken to clarify the appropriateness of the FSR growth curve. Section 6.3.2 outlines the statistical distribution used in the analysis and Section

6.3.3 the derived study growth curve.

6.3.2. Statistical distribution

The hydrological statistical analysis undertaken is based on the L-Moments distribution fitting techniques presented in the FEH and Hosking et al 1997. The statistical analysis using L-Moments is described in further detail in Appendix D2.

Utilising the L-Moments technique to the study data sets, the most representative distribution is determined by the proximity of site L-Moment ratios to the theoretical distribution. Figure 6-7 illustrates that most of the site L-Moment ratios, including the study weighted average (weighted based on gauge record length) are in a closer proximity to the theoretical GEV distribution as opposed to GL. On this basis, the GEV distribution was found to be the most appropriate distribution for the analysis of the Lee catchment. This finding appears to be consistent with ongoing research being undertaken by the Flood Studies Update researchers on catchments throughout Ireland.

Due to the potential influence of the operation of the hydroelectric reservoirs on the distribution of extreme flows, it is proposed that averaged L-Moment ratios excluding the downstream Lee gauges (19013, 19012 and 19011) are used.


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GL

GEV

-0.1

0

0.1

0.2

0.3

0.4

0.5

-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

L-Skewness

L-K

urt

osis

Study Averaged (Total) Study Averaged (Without Gauges D/S of Reservoirs)

Figure 6-7 Hydrometric gauge L-Moment ratio diagram compared with theoretical GEV and GL distributions

6.3.3. Growth curve

The growth curve has been derived by undertaking the statistical analysis at individual stations and pooling (averaging) the underlying statistical properties (L-Moments). This approach mitigates against spatial dependence influences that could have been apparent if a station-year statistical approach was used.

The study averaged L-Moment ratios (Figure 6-7) form the basis of the inputs to the GEV study growth curve. Figure 6-8 compiles annual maximum records from all analysed hydrometric gauges in relation to the derived study growth and the standard FSR Ireland growth curve. Of note is the close proximity of the derived study growth curve with the FSR Ireland growth curve, suggesting that the FSR Ireland growth curve is appropriate for use for events in excess of that supported by the statistical record.

However, significant outliers do exist to the study average growth curve. In particular gauges 19012 (Lee @ Leemount Lower), 19014 (Lee @ Dromcarra) and 19006 (Glashaboy @ Glanmire) all suggest a growth curve well in excess of the study growth. Conversely 19011 (Lee @ Leemount Upper) and 19018 (Shournagh @ Tower) tend significantly flatter than the study average.

Although the Lee gauges downstream of the hydroelectric reservoir (19013, 19012 and 19011) are not of direct interest in developing the study growth curve, their divergence from the study average trend may be indicative of the influence of the reservoir operation. In relation to the 19013 and 19012 gauges, the 19011 malfunctioned (gap, visible chart discrepancy or inconsistent with flows at other gauges) for 7 out of the top 15 events recorded


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by the 19012 gauge, and has omitted the three highest recorded events on the Lee. The omissions have the effect of causing lesser events to be plotted as a high return due to the long length of record period. Conversely the period of record of the 19012 gauge omits long periods of middle range events recorded by the 19013 and 19011 gauges. The record starts 9 years (1958) after the 19011 gauge and 15 years (1964) after the 19013 gauge and also omits records between 1994 and 2000. An approximate correlation can be obtained with the 19013 gauged record (r2=0.62), allowing an indicative extension of the record. Based on the extended record the estimated Q100/Qmed ratio reduces from 2.74 to 2.19 (10% above the study growth curve).

Similarly, three of the highest five events, including the highest recorded event in November 2000 appear to have been missed in the 19018 record in relation to the downstream 19015 gauge, explaining the flatter curve. Likewise the relatively short and recent records of the 19006 and 19014 gauges (16 and 20 years respectively) appear to skew recent extreme flood events to shorter return periods. For example, the 11 May 2000 event was classified as a 1 in 10 year event at the 19006 gauge based on 16 years of record, but as a 1 in 50 and 1 in 41 year event on the longer nearby 19015 and 19020 gauges.

2 5 10 20 50 100

0

0.5

1

1.5

2

2.5

3

0 1 2 3 4 5

Logistic Reduced Variate

Gro

wth

fact

or (Q

/Qm

ed)

FSR Growth Curve for Ireland

Study Growth Curve

19001

19006

19011

19012

19013

19014

19015

19016

19018

19020

19031

Figure 6-8 Site indexed annual maximum floods compared with pooled growth curve and the FSR Ireland growth curve

While considerable scatter does exist from the study growth curve, the scatter appears to be attributable to period of record rather than spatial variation in growth curve patterns or influence of the operation of the hydroelectric reservoirs. On this basis, it is proposed that one indicative study growth curve would be appropriate for the study area. The pooling


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approach used provides a weighting based on length of record at the gauges, ensuring that outliers attributable to short records have a lower influence on the overall curve.

Figure 6-9 illustrates the 95%ile confidence limits of the pooled growth curve. The confidence interval is a function of the length of data record, variability between data records and the return period. The confidence limits have been derived by a Monte Carlo sampling with a sample size of 10,000 in accordance with the techniques outlined in Hosking et al 1997.

The FEH recommends that a pooling group with a data record of five times the return period is used. However, the FEH recommendation is based on existence and access to a substantial national flood record. Where a single site analysis is undertaken, the FSR recommends that return periods should only be extrapolated up to twice the length of the record.

As all of the pooled gauges are contained within the study area, they could be considered to be both operating as a single site gauge and a pooled gauge. The total record used, excluding gauges on the Lee downstream of the reservoirs is 157 years, with an average data record of 20 years. Therefore, based on the FSR single site analysis, a return period of 1 in 40 years would be supported from the data record. However, the derivation of confidence limits allows for a greater return period to be derived, if the confidence limit is considered appropriate.

Based on close correlation with the FSR Ireland growth curve for return periods less than 50 years and the accurate confidence limit (upper 95%le limit at 15%), the study pooled growth curve is used for estimates less than 50 years and the FSR Ireland growth curve for all estimates above. In turn, the containment of the FSR Ireland growth curve within the study pooled 95%le confidence limits confirms the appropriateness of the FSR Ireland growth curve to the study.

Return Period (yr)

2 5 10 20 50 100 200 10000.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0 1 2 3 4 5 6 7

Gumbel Reduced Variate

Gro

wth

facto

r (Q

/Qm

ed

)

Pooled Growth Curve Pooled 95%ile FSR Growth Curve

Figure 6-9 Pooled growth curve and 95%ile confidence limits in relation to FSR Ireland growth curve


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Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4

0 1 2 3 4 5 6 7 8


Gro

wth

facto

r (Q

/Qm

ed

)

Study Growth Curve Study 95%le

Figure 6-10 Study growth curve with 95%ile confidence limit

Table 6-4 Study growth factors

Return Period Y (GEV) Study QT/Qmed FSR QT/Qmed

2 0.4 1.0 1.0

5 1.5 1.3 1.3

10 2.3 1.5 1.4

20 3.0 1.7 1.6

50 3.9 1.8 1.9

100 4.6 2.1 2.1

200 5.3 2.3 2.3

1000 6.9 2.7 2.7

It is debatable whether the confidence limit for return periods greater than 1 in 50 year should be the FSR Ireland or the study growth confidence limits. This study has adopted the confidence limit derived from the study data as the study growth curve limits provide direct consideration of flood variability within the catchment.


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Appendix D contains further details of the growth curve analysis undertaken at individual gauges.

6.4. Calibration hydrology

6.4.1. Introduction

Model calibration, where data supports this, is achieved through carrying out simulations of recorded flood events and then inferring adjustments to the hydraulic model parameters through the comparison of observed and modelled results. Often the variables are quite interdependent, but are also not necessarily constant between event periods, so more than one event will be used to provide a comparison and an indication of parameter variability. Calibration depends on several factors, such as:

• The amount of data available for each event;

• The reliability of the recorded data sets; and

• The extent of suitable event records.

The use of more recent events is preferred, particularly where changes have been made to the river. To support this approach a total of six events were initially selected for possible calibration/verification purposes with four of the events occurring within the last seven years (as detailed in Section 4.4).

Although there is a relatively good spread of data recording points available within the Lee catchment, it was found that the data availability from these gauges was poor. To enhance the calibration process a variety of historical sources of information were sought, including:

• Full review of available flood reports and information from the OPW website and other sources. Appendix A and B detail the data collection and record of documents reviewed and flood information obtained.

• Meetings were held with Local Authority Area Engineers to inform on past flood

events. • As part of the channel and cross section survey, the surveyors liaised with the Local

Authority Area Engineers to obtain local information on any additional areas where historic flood levels could be surveyed during the Lee survey – no further advice was given to the surveyors on historic flood levels.

• There was limited detailed information available through the reports in terms of water levels, exact flood locations and detailed flood mechanisms. Using the limited information the team pieced together (using a GIS shape file layer per river, per event) locations where bridges surcharged, flows were noted to go out of bank, etc. This was supplied to the hydraulic modellers to allow a further ‘check’ on areas where spilling/surcharging should be expected from the hydraulic models.

• More recent flood events were documented by the project team, for example the 2006 event. A site visit was undertaken and a technical note written on the event, including a map of the estimated flood extent.

Full details describing the suitability of each proposed calibration event, for each model, are included in Sections 6.4.3 to 6.4.6. The results of the model calibration will be reported on in the Hydraulics Report.


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6.4.2. Flow distribution approach

Where a flow gauge was located near the downstream end of the catchment, distribution throughout the catchment via a flow per unit area approach was adopted. Where gauges were located in the upper catchment (such as gauge 19020 on the Owennacurra) or where some sub-catchments were ungauged (such as the Curragheen River subcatchment) an infilling technique was used to account for flow in these areas. This utilised the rainfall distribution for the event based on generating rainfall contours for all available rain gauges for the event. The distribution was based on two steps:

(i) Estimation of ratio of un-gauged sub-catchment areas to gauged area.

(ii) Analysis of rainfall distribution for the event and estimation of average rainfall per sub-catchment area in order to establish a scaling factor.

This detailed analysis allowed the distribution of flow throughout the Lower Lee catchment to be estimated with more confidence.

6.4.3. Upper Lee

August 1986

Inflow boundary

ESB data for the 1986 calibration event was digitised for two gauges (19031 and 19027) on the Sullane and Laney respectively. The data available for this event was limited and of poor quality. No information on the peak stage is available for gauge 19031 because the chart was submerged during the event. The peak was therefore estimated and the recession curve calculated by scaling the recession curve from a previous event. No information is available for the upper Lee gauge 19014 for this event. However, the report written on the River Lee flood of 5 & 6 August 1986 has been used to further inform the 1986 flood event in the upper Lee catchment. Charts from the report showing the inflow, outflow, and water levels of the Carrigadrohid and Inishcarra reservoirs have been used to inform the integration of the hydrology for this event to the hydraulic model. Several of the graphs from the report have subsequently been digitised to aid in the calibration of this river reach.

Downstream boundary

The downstream extent of the upper Lee model is represented by the operation of the reservoirs. Information from the ESB report on the 1986 flood event was used to inform the total discharge from the reservoir, composed of two components; the flow through the turbines and flow through the spills.

Observed information

The model is being calibrated against: the water level and flow at gauge locations, the recorded reservoir levels and by using historic information on which areas were known to have flooded based on anecdotal evidence.

December 2006

Inflow boundary

There is no flow data available for flow gauge 19031 on the Sullane for this event. Flow data is available for flow gauge 19014 on the Laney. Extensive written information and flood


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mapping is available for the flooding in Baile Mhic Ire and Baile Bhuirne. With such records of the flooding extent available it is an ideal calibration event to use.

Therefore, to overcome the lack of flow data and make the most use of the recorded flood extent, it was decided to obtain rainfall data for the upper Lee catchment and use this, along with catchment area, to infill the flow in gauge 19031 from gauge 19014.

Rainfall data was obtained for two rain gauges in both the Sullane (19031) and Laney (19014) catchments:

• Macroom – Curraleigh (19031)

• Coolea – Milleens (19031)

• Gouganebarra (19014)

• Ballingeary (Voc. Sch) (19014)

An average of the daily rainfall data for the December event was obtained for each of the 19031 and 19014 catchments respectively. This was used along with the catchment area to obtain a relationship between the gauges. The 19031 gauge was found to be 1.15 greater than the 19014 gauge. This information was used to infill gauge 19031 and subsequently the 2006 event was able to be used for calibration purposes.

Downstream boundary

The downstream boundary does not influence the gauging station location, therefore a generic boundary was used. This consisted of undertaking sensitivity to the water level downstream to check there was no influence at the site and adopting an arbitrary water level.


The model is being calibrated using the detailed technical note produced by Halcrow following the December 2006 flood event for the area which suffered from flooding, Baile Mhic Íre (ref: TN007.SiteVisitNotes_FloodingDecember2006.PD.doc). .

6.4.4. Lower Lee

November 2002

Inflow boundary

Recorded flow data is available for flow gauge 19011 (Lee), 19012 (Lee), 19013 (Lee), 19015 (Shournagh) and 19016 (Bride (south of River Lee)). No flow data is available for flow gauge 19018 on the Shournagh. The gauges are spread amongst the lower Lee catchment and it is felt that adopting a flow per unit area approach based on the flow at these gauges is sufficient to distribute the flow amongst the catchment. For the Lower Lee ungauged sub-catchment areas (lowlee5-lowlee10 and lowlee13) a scaling based on the rainfall and area relationship with other local gauges was used.

Differences in flow readings were noted between the hydroelectric reservoir outflow records (composed of spill releases and turbine releases) and flow gauge 19013 (situated immediately downstream of the reservoir). The reservoir daily load report sheets logging releases were used within the calibration event as these were felt to be more representative of the flow in the river immediately downstream of the dam.

Downstream boundary


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A tidal boundary including surge was extracted from the Cork Harbour model. The model was run using recorded tidal data to produce a tidal boundary at the downstream boundary of the river model.


The model is being calibrated against the water level and flow at gauge locations, particularly 19015, 19016 and 19012, and by using historic information on the extent and nature of flooding in specific areas.

October 2004

Inflow boundary

Recorded flow data is available for flow gauges 19011, 19012, 19013 on the Lee and 19016 on the Bride (south of River Lee). No flow data is available for flow gauges 19015 or 19018 on the Shournagh. As for the 2002 event, the gauges are spread amongst the lower Lee catchment and it is felt that adopting a flow per unit area approach based on the flow at these gauges is sufficient to distribute the flow amongst the catchment. For the lower Lee ungauged sub-catchment areas (lowlee5-lowlee10 and lowlee13) a scaling based on the rainfall and area relationship with other local gauges is used.

There was no record made available of flow releases from Inishcarra reservoir. As this event is a tidal event, it is assumed that the tidal conditions will have driven the flooding and that the fluvial input will be secondary. Therefore a nominal flow of 80m3/s has been adopted as the release from the reservoir into the lower Lee. This magnitude is supported by the ESB Regulations & Guidelines for the Control of the River Lee.

Downstream boundary



The model is being calibrated against the water level and flow at gauge locations, particularly gauge 19016 and 19012, and by using historic information on where flooding was recorded as having occurred.

December 2006

Inflow boundary

Recorded flow data is available for flow gauges 19011 (Lee), 19015 on the Shournagh and 19016 on the Bride (south of River Lee). No flow data is available for flow gauges 19012, 19013 on the Lee or the other gauge on the Shournagh (19018). As for the other events, the gauges are distributed around the lower Lee catchment and it is felt that adopting a flow per unit area approach based on the flow at these gauges is sufficient to distribute the flow amongst the catchment. For the lower Lee ungauged sub-catchment areas (lowlee5-lowlee10 and lowlee13) a scaling based on the area relationship with other local gauges was used. No rainfall data was available for this event so the rainfall scaling factor has been assumed as 1.0. As for the November 2002 event, the reservoir logged releases were used within the calibration event in place of flow data from gauge 19013.


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Downstream boundary



The model is being calibrated against: the water level and flow at gauge locations, particularly gauges 19015, 19016 and 19011. The model will also be calibrated against recorded water level data from the waterworks weir in Cork City and by using historic information on which areas were known to have flooded.

6.4.5. Glashaboy

November 2002

Inflow boundary

The available flow data came from flow gauge 19006 on the Glashaboy, which is located in the lower catchment.

Downstream boundary

A tidal boundary including surge was extracted from the Cork Harbour model for this event based on recorded levels in Cork Harbour.


The model is being calibrated against: the water level and flow at the gauging station location and by using anecdotal information on flooding that occurred during the event.

October 2004

Inflow & downstream boundaries

As for the 2002 event, the available flow data came from flow gauge 19006 and a tidal boundary was extracted from the Cork Harbour model.


The model is being calibrated against the water level and flow at the gauging station location and by using historic information on the extent and nature of the flooding.

6.4.6. Owennacurra

November 2000

Flow boundary

The available flow data came from flow gauge 19020 on the Owennacurra, which is located in the upper catchment (representing an area of approximately 45% catchment area).

Downstream boundary

It was not possible to obtain a tidal boundary for this event from the Cork Harbour model as there is no electronic tidal record available for this time period. Without a record of the actual


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water levels in the harbour there is no way of knowing what the surge, and thus the actual water level, was at that time. However as this event was a fluvial flood event rather than tidal a generic tidal boundary is being used and sensitivity analysis will be carried out to assess any potential impact on the predicted water levels in the river model.


The model is being calibrated against historic information on which areas were known to have flooded along the Owennacurra.

October 2004

Flow boundary

The available flow data came from flow gauge 19020 located in the upper catchment of the Owennacurra.

Downstream boundary



The model is being calibrated against historic information on the extent of flooding in the catchment.

6.4.7. Owenboy

November 2002

Inflow boundary

The available flow data came from flow gauge 19001 on the Owenboy, which is located in the lower catchment.

Downstream boundary



The model is being calibrated against the water level and flow at the gauging station location and using the available information on historic flooding along the Owenboy.

October 2004

Inflow boundary

The available flow data came from flow gauge 19001 on the Owenboy, which is located in the very downstream catchment.

Downstream boundary



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The model is being calibrated against the water level and flow at the gauging station location and by using historic information on which areas were known to have flooded in the catchment.

6.4.8. Summary of calibration/verification events

Table 6-5 summarises the calibration/verification events suitable for use following a review of the flow data and supplementary information. For many events, in particular on the Lee main channel, it is apparent that there is not consistent flow gauging information available for all events. Table 6-6 details the respective flow gauges and the availability of data per event. Despite the lack of data it was possible, via the use of infilling using rainfall data for example, to produce two calibration/verification events for each river model. Some of the events represent flooding throughout a river reach, where as others represent a specific area in the catchment, for example Baile Mhic Íre on the Sullane in the upper Lee catchment in December 2006. Using techniques to utilise as much of the available flow and rainfall data as possible, has allowed for crucial recorded flood extents in urban areas to be utilised. This approach has led to a reduced level of uncertainty in the hydraulic modelling.

Table 6-5: Actual calibration/verification events for the Lee and tributaries

River Model Aug 1986 (Fluvial)

Nov 2000 (Fluvial)

Nov 2002 (Fluvial)

Oct 2004 (Tidal)

Dec 2006 (Fluvial)

Upper Lee ��

Lower Lee ��

Glashaboy ��

Owennacurra ��

Owenboy ��


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Table 6-6: Detail of availability of flow gauge data for calibration events

Flow gauge

Model Aug 1986 Nov 2000 Nov 2002 Oct 2004 Dec 2006

19001 Owenboy ��

19006 Glashaboy ��

19011 Lower Lee ��

19012 Lower Lee �� 0

19013 Lower Lee �� 0

19014 Upper Lee 0 ��

19015 Lower Lee �� 0 ��

19016 Lower Lee ��

19018 Lower Lee 0 0 0

19020 Owennacurra ��

19031 Upper Lee �� 0

(Key: �� Data available 0 Data not available)

6.5. Design hydrology

6.5.1. Unit hydrograph

The FSR unit hydrograph technique enables the use of study specific unit hydrographs. This flexibility allows for incorporation of hydrograph shape and response characteristics that are representative of the study catchment characteristics. Development of study unit hydrographs are limited to gauged catchments with rainfall patterns that may be represented by those recorded at the two hourly rain gauges (Cork Airport and Roches Point (pre 1994)). Given the few gauged catchments falling in to this criteria (19001 - Owenboy and 19016 - Bride), the spatial validity of the hourly rain gauge record was extended by developing event two day isohyetal plots, and scaling the gauge hyetograph. This technique refined the derived unit hydrographs from 19001 and 19016, and facilitated the development of unit hydrographs at Owennacurra (19020).

At least three events were extracted and averaged for each gauge, rebased to units consistent with the standard FSR unit hydrograph parameters and plotted together with the FSR (Figure 6-11). It is worth noting that considerable variation in the unit hydrograph peak exists for alternative events considered at each gauge (+/- 60%) and alternative gauge averages across the study area (+/- 65%). However the FEH donor catchment technique used in this study ensures that hydrographs are calibrated to gauge statistical record and are not directly sensitive to unit hydrograph peak. The study derived unit hydrographs do however provide a depiction of hydrograph shape, which is particularly critical for inflows to the hydroelectric reservoirs.


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The FEH donor catchment techniques used in this study require the adoption of one averaged study unit hydrograph. Without the common unit hydrograph the spatial distribution of the SPR and Tp scale parameters would not be feasible.

Despite the large variation in unit hydrograph peak, the study average peak is close to the FSR peak (within 13%). However, the shape of the study hydrograph has a narrower peak than the FSR, and longer recession. This variation could be due to over simplification of the FSR unit hydograph (three points as opposed to the more realistic five points used here), which has been rectified in the recently published FEH Supplementary Report 1 (CEH, 2007).

The study average unit hydrograph is considered to reflect the broad hydrograph shape characteristics experienced in the study area, and on this basis has been used in the generation of design flows.

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0.0 1.0 2.0 3.0 4.0 5.0 6.0

T/Tp

Up

.Tp

(m

3/s

.hr/

10cm

/km

2)

19001

19016

19020

FSR

Study Average

Figure 6-11 Averaged Unit Hydrographs at Lee Hydrometric Gauges Compared with Flood Studies Report Unit Hydrograph

6.5.2. Storm - flood return period relationship

One inherent difficulty with a rainfall runoff approach is while the model can be calibrated to match statistical derived design floods at a defined return period (or in the case of this study the index flood Qmed), the model does not automatically guarantee that rainfall-runoff derived flood peaks match the statistically derived floods for different return periods. The FSR approached the discrepancy by defining an averaged relationship between flood return period and storm return period (FSR Figure I6.54) where recommended FSR catchment characteristics are used. However, within the seven catchments considered by the FSR, considerable variation existed. For example, the FSR found that the 50 year flood was produced from storm return periods ranging between 60 and 128 years, averaged at 81 years.

Rigid application of the FSR relationship ignores regional growth curve differences, particularly relevant in the case of FSR application in Ireland (UK rainfall growth curves used in conjunction with Ireland regional flood growth curve) or in the case of this study, where study specific rainfall and flood growth curves have been developed. The discrepancy between rainfall and hydrology growth curves has been addressed in this study by defining a


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study specific growth curve relationship (Table 6-7). Further discussion on the altering of the growth curve relationship is provided in Appendix D2.

An increased divergence between study and FSR storm-flood return periods is apparent for flood return periods greater than 50 year. This divergence is attributable to variation and limited sample of the underlying FSR data, variance between the FSR catchment sample and the Lee Catchment and the use of an alternative rainfall and flow growth curve combination.

Table 6-7 Study flood-storm return period relationship compared with the Flood Studies Report

Storm Return Period (yr)

Flood Return

Period (yr) Recommended

Study

Flood Studies

Report

2 2 -

5 8 8

10 17 17

50 56 80

100 98 140

200 173 -

1000 578 1000

6.5.3. FSR unit hydrograph analysis

All design flow hydrographs were derived using the FSR unit hydrograph method, including formula revisions recommended in the Flood Studies Supplementary Report 16. The parameters used, analysis and results are outlined in further detail in Appendix D.

Deviations to the FSR unit hydrograph method were made where both site data facilitated a further refinement to standard FSR parameters and where subsequent developments in hydrological techniques warrant an alternative approach (Sections 6.2.3, 6.5.1 and 6.5.2).

Subcatchment characteristics were found to be broadly similar throughout the study area (Figures 6-12 to 6-15). In general, most subcatchments are small rural catchments characterised by the FSR as low runoff material. While the calibration of the runoff parameters through the donor catchment approach suggests that the FSR soil runoff is overly simplistic, the total catchment area averaged SPR values are still broadly consistent between the two methods.


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0

5

10

15

20

25

30

35

40

0-25 25-50 50-75 75-100 100-125 125-150 150-175 175-200 200-225 225-250 250-275

Cat chment Ar ea ( km 2 )

Figure 6-12 Sub catchment unit hydrograph catchment characteristics based on sub catchment area.

0

5

10

15

20

25

30

35

40

0-0.05 0.05-

0.1

0.1-

0.15

0.15-

0.2

0.2-

0.25

0.25-

0.3

0.3-

0.35

0.35-

0.4

0.4-

0.45

0.45-

0.5

0.5-

0.55

0.55-

0.6

0.6-

0.65

0.65-

0.7

0.7-

0.75

Ur ban Fr act i on

Figure 6-13 Sub catchment unit hydrograph catchment characteristics based on urban fraction

0

5

10

15

20

25

30

35

40

45

50

15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 75-80

Uncal i br at ed SP R ( %)

Figure 6-14 Sub catchment unit hydrograph catchment characteristics based on SPR (before donor catchment scaling)


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0

5

10

15

20

25

15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 75-80

Cal i br at ed SP R

Figure 6-15 Sub catchment unit hydrograph catchment characteristics based on SPR (after donor catchment scaling).

Table D18 in Appendix D summarises the peak flow predicted at all subcatchments for the existing, mid range and high end future scenarios respectively (refer to Section 8.4.5 for discussion on the future scenarios). Design flows are provided for the critical storm duration in Table D19, and full hydrographs for a range of durations in the electronic data DVDs supplied with the report.

6.5.4. Design flow confidence limits

The design flow confidence limit is both a function of the Qmed uncertainty and the growth curve uncertainty. The confidence limit can vary spatially based on whether the estimate is from a gauged or ungauged catchment (Section 6.2) and with return period (Section 6.3.2).

For most applications, it will be sufficient to use the study average Qmed 95%ile confidence limit of 1.41 (Section 6.2.4), with the appropriate return period confidence limit. Figure 6-9 indicates that the close proximity of the FSR Ireland growth curve with the upper 95%ile confidence limit results in little variation in the confidence scale factor. Where inclusion of the 95%ile confidence limit is required in flood estimates (for example, Section 50 applications), it is recommended that design flows provided in this study are scaled by an average factor of 1.52.

Section 8.6 outlines the recommendations for the inclusion of confidence scale factors in the Lee CFRAMS.


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Table 6-8 Confidence limit scaling factor

Annual Exceedance Probability

Return Period (year)

Upper 95%ile confidence limit

scale

50% 2 1.53

20% 5 1.50

10% 10 1.51

5% 20 1.52

2% 50 1.55

1% 100 1.52

0.5% 200 1.52

0.1% 1000 1.48

6.6. Sensitivity to changes in catchment parameters

Design flow rates are sensitive to changes in both catchment runoff parameters and rainfall parameters. Figures 6-16 to 6-19 illustrate the percentage change in maximum flow rate to a 20% change in catchment or rainfall parameters.

A 20% increase in SPR is predicted to result in a 7%-16% increase in design flow, with an increasing sensitivity in catchments with higher soil runoff conditions (Figure 6.16). Conversely, catchments with lower soil runoff conditions are particularly sensitive to changes in Catchment Wetness Index (CWI), with a 20% increase in CWI resulting in a 9%-24% increase in design flow (Figure 6.17). As could be expected, increases in the urban extent results in increases in design flow, with 20% proportional increases in existing partially urbanised catchments resulting in an increase in flow of 12% (Figure 6.19). As an indication of the sensitivity of the catchment to climate change, a 20% increase in design rainfall (M5-2Day) will result in an expected corresponding 20% increase in flow (Figure 6.18).

The sensitivity analysis found that design flows are highly sensitive to changes in design rainfall and catchment wetness index. The analysis undertaken has assisted in reducing the uncertainty associated with the design rainfall by undertaking a statistical analysis of meteorological records in the catchment and revising FSR rainfall contours. The FEH donor catchment approach used also assists in accounting for discrepancies in CWI within the SPR scale parameter.


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0

5

10

15

20

25

0 10 20 30 40 50 60

Catchment SPR (%)

Incre

ase in

flo

w (

%)

Figure 6-16 Change in maximum design rainfall as a result of 20% change in SPR*

0

5

10

15

20

25

0 10 20 30 40 50 60

Catchment SPR (%)

Incre

ase

in

flo

w (

%)

Figure 6-17 Change in maximum design rainfall as a result of 20% change in CWI*

0

5

10

15

20

25

0 10 20 30 40 50 60

Catchment SPR (%)

Incre

ase

in

flo

w (

%)

Figure 6-18 Change in maximum design rainfall as a result of 20% change in M5-2Day rainfall*


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-5

0

5

10

15

20

25

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

Existing Urban Fraction

Incre

ase in

flo

w (

%)

Figure 6-19 Change in maximum design rainfall as a result of 20% change in urban fraction

* Plots are indexed to the catchment SPR value


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7. Integration of hydrology and hydraulic modelling

7.1. Sub-catchment delineation

7.1.1. Introduction

The Lee catchment extends to approximately 2000km2 in area. In order to represent the hydrological processes in sufficient detail to enhance the hydraulic modelling outputs, it was necessary to sub-divide the catchment into smaller sub-catchment areas.

7.1.2. Approach

Using GIS software, Ordnance Survey Ireland (OSi) background maps and the hydrologically corrected DEM, the Lee catchment was further sub-divided. It was necessary to ascertain the downstream location of each of the sub-catchments required. This process was undertaken based on the knowledge of rural and urban watercourses; reservoir locations, hydraulic features, flow gauge locations and locations of significant tributaries. GIS tools allowed for the calculation of each of the respective sub-catchment areas which were then fed into the hydrological analysis. The sub-catchment boundaries were based on the following hypothesis:

(i) Boundaries to be fixed at flow gauges (being used in the study) and/or

(ii) Boundaries to be fixed at upstream of hydraulic models and/or downstream of urban areas

(iii) Boundaries to be fixed at strategic areas e.g. downstream of reservoirs, such as Inishcarra Dam

7.1.3. Sub-catchments

Figure 7-1 shows the 56 sub-catchment areas derived so as to provide detailed hydrological inputs into hydraulic models for the Lee CFRAMS. A table showing the reasoning behind the specific sub-catchment locations is included in Appendix E.

As shown on Figure 7-1, 32 sub-catchments will be used to derive detailed hydrological assessments; that is a design flow hydrograph will be produced for each of these 32 main subcatchments. To represent the hydrological processes in sufficient detail to allow integration with the hydraulic modelling it was necessary to further sub-divide some of the 32 main subcatchments resulting in an additional 24 subcatchments for which inflows are required. The inflows for each of these 24 subcatchments will be scaled from the design flows derived for the main subcatchment within which they are located. The scaling is based on both area and urban fraction. In some instances, the subcatchment flows are input into the hydraulic models as both point and lateral inflows resulting in a total of 108 inflow locations in the Lee catchment hydraulic models (not all lateral inflows are shown on Figure 7-1).


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Figure 7-1 Sub-catchment delineation

7.2. Hydraulic model inflows

7.2.1. Approach

To enhance the accuracy of the hydraulic modelling and flood mapping process, three types

of hydrological inflows were identified to be used to feed into the hydraulic models:

• Point inflows at upstream hydraulic model extents

• Point inflows at strategic locations throughout the catchment (e.g. tributaries, natural watercourses)

• Lateral inflows through urban areas (to represent surface water runoff) to allow the flow being fed through urban area watercourses to be modelled with more detail.

Utilising the GIS layering capabilities of separate spatial data sets it was possible to assess the integration of the catchment runoff with the topographical survey cross sections and the hydraulic model schematisation. Knowledge of the location of natural inflows from background maps and other information, such as the extent of rural and urban watercourses, allowed the identification of the respective hydraulic model cross section where the inflow was required. Using this information the hydrological analysis was made interdependent with the hydraulic modelling with details of inflow location, type of inflow and fraction of catchment represented by the inflow location. The information provided for the calibration models is included in Appendix E2. Further descriptions of the hydrology / hydraulic links will be provided in detail in the Hydraulics Report.

An example of the sub-catchment delineation and inflow location for the Owenboy catchment is shown in Figure 7-2. The Owenboy catchment is one of the 32 main subcatchments in the Lee catchment (Section 7.1.3) and has been further subdivided into ten subcatchments to


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allow representation of five tributaries and three urban areas as well as the upstream Owenboy catchment.

As shown on Figure 7-2, ten inflows are required to satisfy the hydraulic model requirements, based on the ten subcatchment areas.

Figure 7-2 Example of integration of hydrology and hydraulic modelling for the Owenboy hydraulic model

7.2.2. Inflows

Table 7-1 lists the number of hydrographs and total number of inflows to be derived for each model.

Table 7-1 Breakdown of hydrographs and inflows per hydraulic model

Model Number

hydrographs

Number of sub-

catchment inflows

Number of inflow

locations*

1 – Owenboy 1 10 10

2 – Carrigtohill 2 4 8

3 – Owenacurra 3 6 9

4 – Glashaboy 3 5 10

5 – Upper Lee 8 8 20

6 – Tramore 1 5 8

7 – Bride 3 3 6

8 – Lower Lee 11 15 48

Total 32 56 119

* this includes lateral inflows with a count of 1 per reach of lateral inflows


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8. Future environmental and catchment changes

8.1. Introduction

There are a number of drivers that can influence future flood risk in the Lee catchment. These include changes in climate, land use and urban growth. As these are likely to change over time it is important to appreciate how the drivers could affect future flood risk across the catchment. To achieve this, it is necessary to test possible future scenarios to help in considering what protection levels may be required to protect against future flooding.

This section sets out the possible implications of climate change (Section 8.2), afforestation (Section 8.3) and urban development (Section 8.4) on the hydrological processes in the Lee catchment and proposes two future flood risk management scenarios (Section 8.5). Section

8.6 describes the two future scenarios adopted for use in the Lee CFRAMS.

The potential impact will be tested within the hydraulic models assessed as part of the Lee CFRAMS. The impacts of the future drivers on flood risk will be documented in the Lee CFRAMS Hydraulic Modelling Report

8.2. Climate change

8.2.1. Introduction

“Over the next half-century significant climate change can be anticipated in Ireland….Considerable uncertainty remains with respect to future climate conditions….however forward planning is needed now for adaptation to climate change in Ireland” (Sweeney et al, 2003).

“Our farmers, architects, engineers, planners and politicians will need to adjust to a changing climate regime to protect people and employment, to provide resources such as water and waste water treatment at economic cost, and to position Ireland to adapt to the climatic challenges which lie ahead” (Irish Committee on Climate Change, 2007).

One area where the impact of climate change needs to be considered is in the design of flood relief schemes and flood risk management measures as part of flood risk management policy in Ireland. Changes in sea level and rainfall depths and intensities could have significant implications for flood risk in Ireland and the subsequent design of flood risk management measures and relief schemes. Therefore it is sensible to design such schemes so as to incorporate climate change estimates and to allow for future adaptability.

The 2007 Environmental Protection Agency (EPA) report (McElwain and Sweeney, 2007) identifies the need for planning and action to avoid the worst effects of climate change impacts. The report highlights the need to predict the impacts of climate change at local, regional and national levels in order to enable adaptation strategies to be devised.

An extensive quantity of climate change research exists, both within the UK and specifically in Ireland. A climate change literature review was undertaken (Appendix F1) which considered a wide range of publications, including the latest work from the Intergovernmental Panel on Climate Change (IPCC), the 4th Assessment report (February 2007) and the subsequent Irish Committee on Climate Change report published by the Royal Irish Academy (RIA) (February 2007).


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The aim of the literature review was to provide a range of potential values for sea level rise (Section 8.2.3) and increase in precipitation (Section 8.2.4) within the Lee catchment area. These values will be used to inform the Lee CFRAMS and will be incorporated into potential catchment flood risk solutions, either directly within design levels or through providing future adaptability to defence solutions. The findings may also be used to inform future CFRAM studies in Ireland.

8.2.2. Guidance policy

Ireland

A single, rigid policy for the design of flood relief schemes and flood risk management measures, with respect to the impacts of potential changes in the climate, has not as yet been adopted by the OPW. A provisional policy is, however, in place, whereby the predicted increases in flows and / or water levels are to be included where possible.

The current OPW operational guidance note ‘Design Considerations of Possible Climate Change for Flood Risk Management Practice’ (2006) requires the following:

• Sea level rise: climate change allowance to be added to design levels in all tidal situations; an additional allowance is to be added on the South Coast for ground level movement. The allowance is to be considered as a component of the design water level and not as freeboard.

• Increase in flood flows:

a) Sensitivity-guided design - whereby the sensitivity of the design of a scheme to climate change is tested e.g. by testing the parameters subject to change, such as peak flow.

b) Design for enhancement - flood relief scheme designed so that defence levels / capacities can be increased / enhanced in the future.

c) Design for climate change – Flood relief works designed to cope with predicted future conditions.

The literature review by Bruen (2003) commissioned by the OPW looked at climate change on a regional scale in Ireland, particularly, likely change in river flows and extreme water levels in coastal areas, during the 21st century.

OPW are currently reviewing their climate change policy and a new policy document is likely to be published in 2008.

UK Defra guidance, England & Wales (2006)

Other policy information was sought from guidance policy recently adopted within the UK by the Department for Environment and Rural Affairs (Defra).

Defra has produced guidance on impacts of climate change for operating authorities (including Environment Agency, Local Authorities and Internal Drainage Boards). Several documents exist to inform climate change consideration: The Flood and Coastal Defence Project Appraisal Guidance - overview (FCDPAG1), sets out the basis for considering climate change; detailed sea level rise allowances are recommended in FCDPAG3; and FDCPAG4 also sets out advice on sensitivity testing.


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Supplementary guidance to FCDPAG3 (Defra, 2006) has been released to reflect most recent findings such as land movement and the effects of thermo-expansion of the sea. The guidance provides new allowances for sea level rise which should be used to determine base cases and options to be compared to the base case. Indicative sensitivity ranges for peak flows, extreme rainfall, extreme waves and winds are given which should be used to test the base case and options to determine how a decision is affected by climate change impacts.

A copy of the supplementary guidance to FCDPAG3 (Defra, 2006) is included as an appendix to this report (Appendix F2). Application of the recent policy to the Lee CFRAMS project has been included for completeness, in Tables 8-1 and 8-2 respectively.

8.2.3. Net sea level rise

The estimations of future net sea level change are based on two components: isostatic changes, which refer to adjustments in the absolute elevation of the land; and eustatic changes, which refer to variations in the absolute elevation of the sea surface caused by variations in the volume of the oceans. Together they are used to estimate net sea-level change, taking into account changes in both land and sea surface level (UKCIP, 2007).

Isostatic subsidence

Southern Ireland is undergoing isostatic subsidence in its recovery from the ice age. At present there is little information on land movement in the Irish context. Recent work in Dublin (Greater Dublin Strategic Drainage Study, 2005) includes estimates of land movement of -0.3mm/yr for the Dublin area. There is a CGPS (continuous global positioning system) receiver measuring land movement at Castletownbere which is in operation, on behalf of DAFF, since 2005. Due to the short period of record of this dataset, it was not considered for use in this study. It is recommended that future reviews should consider the data from this gauge.

Studies in the UK estimate the rate of vertical land movement as -0.5mm/yr in Wales and -1.0mm/yr for south west England (Shennan and Horton, 2002). The Defra guidance policy adopts a value of -0.5mm/yr for land movement for the south west of England and Wales collectively. This latest estimate of -0.5mm/yr is based upon the latest work by Shennan and Horton (2002).

Table 8-1 shows the magnitude of land subsidence that is estimated for three different future time horizons.


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Table 8-1 Land movement (cm) estimates applicable for the Lee CFRAMS from UK literature sources for three future time horizons (baseline for calculating land movement for a given year is taken from 1990).

Land subsidence (cm) Source Land

movement

(mm/yr)* 2050 2080 2100

Shennan and Horton (2002) – Wales -0.5 3.1 4.6 5.6

Shennan and Horton (2002) – SW England -1.0 6.1 9.1 11.1

Defra FCDPAG3 (2006) -0.5 3.1 4.6 5.6

* Negative represents subsidence

Details of the values adopted for use in this study are contained in Table 8-6 and Appendix

F.

Eustatic changes

Global and Ireland specific estimates of change in sea level are available from climate change literature. Table 8-2 shows the range of predicted increases in sea level for three different future time horizons.

It should be noted that all values of sea level rise given in Table 8-2 do not include land movement, except the Defra FCDPAG3 values.

The Defra estimates of global mean sea level up to 2080 are based on the IPCC Third Assessment Report (TAR) (2001) High emissions scenario (A1FI). Projections post 2080 are based on an extrapolation of the 2020s, 2050s and 2080s global mean sea level estimates. The respective IPCC TAR global average sea level rise range, for the 2050s and 2080s respectively is, 9-36cm and 16-69cm.

These precautionary Defra allowances for global mean sea level rise will be reviewed in the light of the IPCC 4th Assessment Report and should be considered in future reviews of this study.


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Table 8-2 Sea level rise (cm) estimates applicable for the Lee CFRAMS from various UK and Irish literature sources for three future time horizons

Sea Level Rise (cm) Source

2050 2080 2100

Comment

IPCC (scenario A2)* 23 - 51 Global average sea level rise

IPCC (scenario A1F1)

26 - 59 Global average sea level rise

UKCIP02 (Medium-High scenario)

15 30 Global average sea level rise

UKCIP02 (High scenario)

18 36 Global average sea level rise

Sweeney et al (2003) 49 Global average sea level rise

Rahmstorf (2007) 55 - 125

Best estimate of sea level rise based on range of scenarios

Defra FCDPAG3 (2006)**

33 65 93 Based on guidance policy [SW England and Wales]

* A2 equivalent to Medium-High UKCIP02 scenario;

** The Defra estimates account for vertical land movement and therefore represent ‘net’ sea level rise

Details of the values adopted for use in this study are contained in Table 8-6 and Appendix

F.

8.2.4. Increase in precipitation and flows

Global and Ireland specific estimates of future increase in precipitation are available from climate change literature. Table 8-3 shows the range of predicted increases in precipitation for three different future time horizons.

The Lee catchment geology of limestone and sandstone aquifers, does not provide a vast amount of storage attenuation in the catchment. Based on this knowledge it is assumed that the percentage change in rainfall translates to the same percentage change in flow.


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Table 8-3 Estimates of increase in precipitation (%) applicable to the Lee CFRAMS from various UK and Irish sources for three future time horizons

Source 2050 2060 2080 2100 Comment

UKCIP02

(Medium-High scenario)

10% 15% Increase in winter precipitation

UKCIP02

(High scenario)

10% 15% Increase in winter precipitation

Sweeney and Fealy (2006)

11%-17%

Increase in winter precipitation

McGrath et al (2005) 10% Increase in December precipitation

Sweeney, et al (2003)

11% Increase in winter precipitation

Defra FCDPAG3 (2006)*

20% 20% 20% 20% Based on guidance policy [peak river flow, for large

catchments]

* The values included represent sensitivity range to be adopted for peak river flow

The values adopted for use in this study are contained in Table 8-6 and detailed in Appendix

F.

8.3. Afforestation

8.3.1. Introduction

Forestry policy in Ireland is implemented in the context of the 1996 Strategic Plan Growing for the Future. The strategy set a target for afforestation in Ireland of 20,000 hectares per annum, after 2000 up to 2035. The increase in forestry was found to be necessary to create the critical mass required to supply a competitive processing sector. Actual average annual afforestation of approximately 14,000 hectares per annum was noted in the period 1996 – 2003 (Peter Bacon & Associates, 2004). The species to be planted will be in the order of 70% conifers and 30% broadleaf species.

8.3.2. Ireland forest cover and practice to date

The Corine 2000 - Ireland Land Cover Update (2004) assessment shows that significant growth in foresty has occurred in Ireland between 1990 and 2000, growing from 10.2% to 11.9%. At present around 15,000 hectares of land area of the Lee catchment is covered by forest cover (Forest Service, 2006). This represents around 12% of the total catchment area. The forests in the Lee catchment are composed of predominately coniferous forest with some broad-leaf forest, and are mainly located in the upper catchment.

The forests are harvested on a 40 to 50 year cycle. All forest operations in Ireland are carried out in compliance with the principles of sustainable forest management (SFM) to meet high environmental, social and economic standards and are implemented through national standards, guidelines and a Code of Best Forest Practice (Forest Service, 2000).


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8.3.3. Afforestation

In the upland areas where forestry is increasingly concentrated, land is usually poorly drained and peaty, so that the soils often require artificial drainage. Pre-afforestation land drainage generally involves the removal of surface water, the drying of the soil and the suppression of vegetation on the overturned turf ridges and in the excavated ditches. The drainage causes an immediate increase in both high and low flows: flood flows tend to be peakier, with shorter response times and higher peaks, whilst baseflows generally increase. In the 10-year period following drainage and planting, there is a tendency for the response times, peak flows and baseflows to begin to regress towards their pre-drainage values. This is a result of the decay of the drainage ditches and infilling with vegetation, in addition to the increasing consumption of water by the growing tree crop. The overall effect of mature forests on flows is still the subject of debate. The steady growth of trees on drained land appears to result in a steady reduction in peak flows, caused largely by a reduction in runoff volumes. It is likely that baseflow will also eventually be reduced as the forest matures further (Flood Estimation Handbook, 1999).

8.3.4. Lee catchment

Forest cover in the Lee catchment is due to rise to around 17% by 2035, in line with government strategy (Forestry Service, 2006). This will increase the catchment area covered by forest by 6,250 hectares to 21,250 hectares. The afforestation will occur in the upper catchment, most likely in the marginal middleground areas, as shown on Figure 8-1. Any new forests will be managed in accordance with SFM principles, including a requirement that broadleaf buffer strips be planted in commercial forests adjacent to streams and rivers to slow runoff (Forest Service, 2000).

Figure 8-1 Landscape character areas within the catchment (Source: Cork County Council)


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8.3.5. Impact on hydrological processes

The impact of change in land use on flood generation is difficult to predict and is perhaps subjective. A range of field trials have been undertaken, producing a variety of results. A project undertaken by Defra/EA in England & Wales, Review of impacts of rural land use and management on flood generation: Impact study report (2005), summarises a variety of field studies. A selection of those studies undertaken on a catchment basis, relevant to afforestation are briefly described below.

(1) Coalburn (England)

Now the longest running experimental catchment in the UK. Catchment discharges have been monitored over a period of more than 30 years, starting in 1967. The various analyses of the study data have revealed significant increases in storm runoff and decreases in the time to peak immediately following drainage, with a recovery to pre-drainage responses after about 20 years. This recovery was interpreted as being the result of forest growth and a decrease in the efficiency of the surface drains, although to a proportionately smaller degree. In the first couple of years following drainage, lag times were about one-fifth to one-third shorter, and hydrograph peaks actually increased by 20% in the first 5 years after forest planting. This demonstrates that in the early stages of afforestation it is the ditches rather than the young saplings that exert the dominant hydrological influence.

(2) Forest of Bowland (England)

A paired catchment study of the effects of forests on water yield, supplemented by a plot-scale study of surface runoff under planted conifers suggested that runoff generation from forest plantations was as large, if not greater than from pasture, at least in the early stages of the growth cycle.

(3) Balquhidder (Scotland)

Comparison of flows in a largely forested sub-catchment and largely grassland sub-catchment. Based on this and other UK studies, Calder (1993b) concluded that conifer forests will reduce water yield irrespective of whether they replace grass or heather moorland. It was found less easy to generalise about the effects of conifer afforestation on low flows; although high evaporation rates from mature, closed-canopy forest can reduce low flows. Land drainage, which is often associated with upland forestry, may increase low flows in the short to medium term.

Evidence that land management changes affect flow in the surface water network

There is quantifiable evidence for the effect of conifer afforestation, but it is difficult to interpret. Most catchment monitoring studies in the UK have focussed on upland catchments dominated by conifer forest or rough grassland. There is evidence that afforestation affects peak flows and times to peak. However, this evidence shows that the impact of forests on flood generation cannot be predicted simply. In their general review of the history of forest hydrology, McCulloch and Robinson (1993) conclude that forests should reduce flood peaks, except for the effects of drainage and forest roads. A review of results from 28 monitoring sites throughout Europe (Robinson et al., 2003) concluded that the potential for forests to reduce peak flows is much less than has often been widely claimed, and that forestry appears to "... probably have a relatively small role to play in managing regional or large-scale flood risk". In summary, there is quantifiable evidence that both afforestation and field drainage can


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affect flows in the surface water network but the impacts can be very different, depending on the local soil type and specific management practices used.

8.3.6. Identification of future stages for Lee study

Research has shown that the impacts of a forest on flood generation in a catchment depends on several factors, such as the amount of surface cover during the year, the stages of the forest life cycle (planting/growing/maturing/logging), and on how forestry operations are managed. The various stages of the afforestation process impact on runoff in different ways e.g. flow, time-to-peak, etc. Therefore it is advisable to consider the impact of these stages on the Lee catchment. It is suggested that the impact scenarios modelled consider two main stages of the afforestation process, as detailed in Table 8-4.

To assess the stages of forest development it is necessary to apply an adaptation to the hydrological parameters. Based on the research of real life studies as detailed in Section

8.3.5, it is proposed to assess the changes to the hydrological parameters Standard Percentage Runoff (SPR) and Time-to-peak (Tp) as shown in Table 8-4. The modifications to SPR and Tp aim to incorporate a range of conditions whereby flood risk would increase and decrease.

Table 8-4 Future afforestation stages – hydrology parameters

Stage Stage of afforestation Change to SPR Change to Tp

1 Clearing of land/drainage + 10% -1/3

2 Mature forest - 10% No change

The suggested stages and parameters are consistent with policy guidance as provided by the Environment Agency for England and Wales, Catchment Flood Management Plan (CFMP) future scenario guidance (2006).

8.3.7. Application to modelling

The afforestation will occur in the upper catchment, most likely in the marginal middleground areas, as shown on Figure 8-1. This area is represented in the ‘Upper Lee’ hydraulic model, and therefore the scenarios suggested in Table 8-4 will be tested for this part of the Lee catchment only.

8.4. Urbanisation

8.4.1. Introduction

The 2006 census indicated that Cork County has an overall population of 480,409; of which 119,143 live in Cork City and in excess of 70,000 in the extensive suburbs. This is a countywide increase of over 30,000 from 2002. This rapidly growing population, linked to increasing immigration and the buoyant economy, presents significant pressure for increased residential, commercial and industrial development and associated infrastructure. Rapid increases in city house prices have resulted in migration from established areas to the new development in the urban fringes creating an urban sprawl around Cork City and the rapid expansion of towns such as Midleton and Carrigtohill. This has resulted in the rapid


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urbanisation of greenfield sites and provided a catalyst for economic regeneration within derelict areas of Cork City. This pattern is likely to continue.

The National Development Plan (NDP) 2007-2013 identified the Cork gateway as the largest urban and economic centre in the South West Region. The National Spatial Strategy (NSS) reinforced that Cork has an immediate potential to be developed to the national level scale required to compliment Dublin, this is also supported by the Cork Area Strategic Plan (CASP).

8.4.2. Ireland urban cover to date

The Corine 2000 - Ireland Land Cover Update (2004) assessment shows that a significant increase in the area of land covered by artificial surfaces has occurred in Ireland between 1990 and 2000, growing from 1.5% to 1.9%. All of these increases are probably related to the economic growth in Ireland in the 1990's and the demand for new housing and commercial premises. There was also an extensive building of new infrastructure (mainly motorways) during this period. Urban development and associated infrastructure covers approximately 3% of the Lee catchment, as shown on Figure 8-2. Development is principally concentrated around Cork City and Harbour and this includes major residential areas, commercial centres and significant industrial areas.

Figure 8-2 Existing urban development in the Lee catchment (based on year 2000 Corine data)

8.4.3. Urban development

It is generally accepted that urban development increases runoff because of the greater impermeability of urban surfaces, which has a marked effect on the flood behaviour of a catchment. Typically it accelerates and intensifies the flood response (Flood Estimation Handbook, 1999).

The 2001 Cork Area Strategic Plan (CASP) estimates that the population of Cork City, its surrounding settlements of Ballincollig, Blarney, Carrigaline, Douglas, Glanmire, Glounthane, Carrigtohill, Midleton and Cobh, ring towns and rural areas will increase by 23% or 78,050


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people over the period to 2020. Average residential densities are expected to be highest in Cork City and along public transport corridors. The overall housing requirement of Metropolitan Cork, over the period to 2020, is estimated to be in the order of 48,700 additional dwelling units. The rural towns of Midleton and Carrigtohill will be under significant residential development pressure, with Midleton predicted to be the largest town (after Cork city) by 2020. The Cork Docklands Development Strategy and subsequent two Local Area Plans (LAPs) detail extensive development in the Cork Docklands area located directly to the east of Cork City centre.

Figure 8-3 shows the spatial distribution of development which is planned to take place throughout the catchment based on the Cork City Council Development Plan and the Cork County Council Development Plan. The urban development area includes residential, industrial, commercial, retail and other infrastructure.

Figure 8-3 Future development in Lee catchment [to time horizon 2020]

8.4.4. Impact on hydrological processes

As identified in Section 8.4.3, the impact of urban development typically accelerates and intensifies the flood response.

8.4.5. Identification of future scenarios for Lee study

The impact of urbanisation on flood generation in a catchment depends on the spatial distribution of the urban cover. As development plans are available for proposed development to 2020, it is suggested that the impact scenarios modelled, as detailed in Table

8-5, consider the planned expansion as detailed in the development plans. An 18% increase in urban growth is predicted to 2020 based on current development plans (compared to Corine 2000 land use data) (equivalent to 0.90%/year). It is suggested that two future scenarios be developed. One scenario: based on rapid growth to 2020 (0.9%/year) with a less rapid growth between 2020 and 2100 (based on current population and projected population figures from the Cork Area Strategic Plan (CASP, 2001) and NCB Stockbrokers report (2006)), a lower rate of urban growth of 13% is predicted from 2020 to 2100 (equivalent


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to 0.16%/year); the other scenario: assuming rapid growth of 0.9%/year throughout, up to 2100.

This is based on a pragmatic and flexible approach, acknowledging that there is a high level of uncertainty associated with predicting development trends many years ahead. As the catchment is undergoing rapid growth the 18% could be considered as a high rate and an upper limit.

The Cork gateway has been identified as the largest urban and economic centre in the South West Region, and the plans in place to expand have been assumed as sufficient to not necessitate the modelling of a low urban growth trend.

To assess the urban development it is necessary to apply an adaptation to the hydrological parameters. It is proposed to assess existing urban development based on the Corine land use data 2000, and future development on the 2020 development plans as shown in Table 8-

5. This process will allow an up-date of the urban hydrological parameter, URBAN, to be achieved.

Table 8-5 Future urban development scenarios – hydrology parameters

Scenario Stage of urban

development

Change to URBAN

1 Based on current development plans

Current urban trend

Growth rate 0.90% increase in urban area per year to 2020 & 0.16% to 2100

2 Based on future development trend

Future urban trend

Growth rate 0.90% increase in urban area per year to 2100

The suggested scenarios and parameters are consistent with policy guidance as provided by the Environment Agency for England and Wales, Catchment Flood Management Plan (CFMP) future scenario guidance (2006).

8.4.6. Application to modelling

The urban development will occur throughout the catchment, as shown on Figure 8-3. Therefore the scenarios suggested in Table 8-5 will be applied to the whole catchment, via application of a change in the ‘urban’ hydrological parameter for each sub-catchment.

8.5. Future scenarios for flood risk management

As detailed in Sections 8.2 to 8.4, there are a number of drivers that can influence future flood risk in the Lee catchment and the estimates of these drivers vary. Table 8-6 collates potential future changes to these drivers, in the form of two future scenarios. The ‘Mid Range Future Scenario’ (MRFS) considers the more likely estimates of changes to the drivers by 2100. To allow for future adaptability of flood defence measures, a ‘High End Future Scenario’ (HEFS) has been included, representing extreme changes in the respective drivers by 2100. It is worth noting that these future estimates will not necessarily impact cumulatively.


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Table 8-6 Relevant combinations of drivers to provide boundaries for future flood risk

Relevant combinations of drivers to provide boundaries for future flood risk

Scenarios Driver

Mid Range Future

Scenario (MRFS)

High End Future Scenario

(HEFS)

Climate change - fluvial flows

+ 20% + 30%

Climate change - net sea level rise

+ 55cm + 105cm

Land use change – afforestation

- 1/6 Tp + 10% SPR

- 1/3 Tp

Land use change – urbanisation

Current urban trend

Growth rate 0.90% increase in urban area per year to 2020 & 0.16% to

2100

Future urban trend

Growth rate 0.90% increase in urban area per year to

2100

The future scenarios will be used when considering the design level of flood mitigation options in the Lee catchment.

• Mid Range Future Scenario (MRFS) - Flood risk management options should be undertaken so as to not impact on existing flood risk in current conditions, and should be adaptable to the MRFS.

• High End Future Scenario (HEFS) - When considering option appraisal, sensitivity analysis to the HEFS should be undertaken to enable the adaptability of each option to be assessed (to cater for more extreme changes in the future).

8.5.1. Explanation of adopted values

(a) Climate change - fluvial flows

MRFS: An increase of 20% to fluvial flow by 2100 is based on Sweeney and Fealy (2006) [17% by 2080 for winter precipitation]. This is supported by Defra FCDPAG3 (2006) guidance policy where 20% is used as a sensitivity range to be adopted for peak river flow.

HEFS: An increase of 30% is assumed based on Murphy et al (National Hydrology Seminar on "Water Resources in Ireland and Climate Change"), predicting streamflow increases of up to 30% for winter months on the Suir catchment.

(b) Climate change - net sea level rise

MRFS: A net sea level rise of 55cm by 2100 is based on Sweeney et al (2003) [49cm by 2100] and incorporating isostatic subsidence of 0.5mm/year [5.6cm by 2100] based on Shennan and Horton (2002) for Wales in the UK. Isostatic subsidence of 0.5mm/year is supported by the Defra FCDPAG3 (2006) guidance policy.


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HEFS: A net sea level rise of 105cm by 2100 is based on Defra FCDPAG3 (2006) guidance policy – as assessed for South West England and Wales. This incorporates isostatic subsidence of 0.5mm/year [5.6cm by 2100] based on Shennan and Horton (2002). In addition a 100mm allowance for surge is incorporated.

Investigations into the effect of climate change on the frequency and severity of storm surges are at an early stage. Initial results modelling up to the year 2100 have produced inconsistent results depending on which models are used. Some models indicate an increase in extreme surge heights whilst others indicate a potential reduction. In view of this high degree of uncertainty, it is not possible at present to give guidance on whether allowances for changes in storm surge due to climate change should be used. However 100mm has been included under the instruction of the OPW.

(c) Land use change – afforestation

MRFS: It is considered unlikely that all areas of large sub-catchments will be subjected to the identical stage of afforestation at any one time, but rather clearing/drainage and mature growth will occur simultaneously in different parts of the sub-catchment. Therefore it is assumed that the clearing/drainage process could increase the SPR by 10%, but that the mature growth stage of the process could decrease SPR by 10% - therefore it is assumed that these changes negate each other and no absolute change to SPR will occur. Tp is estimated to decrease by 1/3 for the clearing/drainage process - this will be further reduced to 1/6 as a result of the average of the two processes.

It is assumed that current land policy practice is adopted until 2100.

HEFS: Assuming that the clearing/drainage process dominates the hydrological process an increase to the SPR of 10% is estimated, with a reduction in the Tp by 1/3.

Changes in land use are normally tested on the catchment scale to gain an indication of the sensitivity of the catchment to change. However it is known that the afforestation in the Lee catchment will occur in the marginal middleground areas of the upper Lee catchment (Forest Service, 2000), therefore changes to the hydrological parameters will be applied to the respective sub-catchments in the upper Lee to enhance representation of the process. By doing this we are localising the possible impacts of afforestation, as would occur in reality. There is no further information available on the exact location of the proposed afforestation over the next 100 years that can be applied. Applying the change in hydrological parameters on an even smaller scale, than we already propose, is not possible or advisable. Research to-date has not provided a detailed relationship on which to support such downscaling of the suggested relationship.

(d) Land use change – urbanisation

MRFS: An 18% increase in urban growth is predicted to 2020 based on current development plans (compared to Corine 2000 land use data) (equivalent to 0.90%/year). As the catchment is under going rapid growth this percentage is considered a high rate and an upper limit on growth. Based on current population and projected population figures from the Cork Area Strategic Plan (CASP, 2001) and NCB Stockbrokers report (2006), a lower rate of urban growth of 13% is predicted from 2020 to 2100 (equivalent to 0.16%/year).

HEFS: The current urban growth trend of 18% by 2020 is assumed to continue to 2100 (equivalent to 0.90%/year).


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The increase in urban growth will be applied to the current urban areas within the Lee catchment.

8.6. Inclusion of confidence limits in Lee CFRAMS

Section 8.5 presents two alternative sensitivity scenarios, based on possible changes in catchment and climatic conditions. Flood confidence limits provide a further representation of the uncertainties in flow estimates and account for the reliability of the underlying data in flood estimates. Where inclusion of flow confidence limits is required in the Lee CFRAMS, Section

6.5.4 recommends that an averaged design flow confidence factor of 1.52 (95%ile confidence limit) is used.

It is recommended that the sensitivity analysis of a design option also includes allowances for the flow confidence limit, as follow:

• Where designing to the Existing Conditions scenario, the sensitivity scenario (Mid Range Future Scenario) shall include the 1.52 confidence limit factor;

• Where designing to the Mid Range Future Scenario, the sensitivity scenario (High End Future Scenario) shall include the 1.52 confidence limit factor.

8.7. Policy to aid flood reduction

8.7.1. Sustainable urban drainage systems

Current evidence suggests that interventions which seek to reduce near-source drivers and pressures associated with land use change are likely to prove most effective and efficient as the drivers themselves are policy driven. This involves discouraging inappropriate land use, farming practices and development where these are clearly linked to increased run-off and flood risk. The diffuse nature of rural land management and related flood generation suggest that, on its own, mandatory regulation would prove ineffective and inefficient, being difficult and costly to administer and enforce, and possibly insufficiently flexible to deal with local circumstances and practices. Instead, the best approach would appear to be a mix of policy instruments: economic and voluntary measures, supported by advice and technical support.

There are many measures that can be taken to mitigate local flooding by delaying runoff from agricultural, forested or developed land using sustainable urban drainage systems such as grass buffers, appropriate ditching permeable surfacing, infiltration/filter trenches, filter strips, soakaways, swales, detention basins, constructed wetlands, and ponds. An integrated approach is needed in applying these measures so that the maximum overall benefit is gained for flood and pollution mitigation and erosion reduction.

At present there is no national policy in Ireland requiring SUDs to be incorporated into new developments, although some local authorities do require sustainable drainage systems as part of planning conditions. In addition, future policy guidance on SUDS may not specify up-take by all types of development; therefore it is difficult at this stage to account for which percentage of future development would apply SUDS. Scenario 1 in Table 8-5 will provide an upper limit on the runoff expected from the planned future development in the catchment. If within future guidance SUDS are enforced then the runoff can be assumed to be lower.

It should be noted that SUDS are normally designed for a specified frequency of event, such as the 3% annual exceedance probability (AEP) event. Therefore it could be assumed that


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when flood producing events with low AEP occur for example 0.5% AEP, even developments with SUDS will not be able to attenuate the runoff.

In the UK, Defra are currently undertaking a study with CIRIA on the effectiveness of SUDS. There is a growing view that they may not be as effective/value for money as postulated and other mitigation measures may be more cost effective. It is recommended that the findings of this study are reviewed and considered in future revisions of this study.

OPW are currently undertaking a study on the Preparation of Guidance on the Consideration of Flooding in Planning and Development Management which is due to be completed in 2008. The output from this study will provide guidance to both local authorities and developers on the appropriateness of developing in flood risk areas.

8.7.2. Operation of the Carrigadrohid and Inishcarra Dams

An opportunity appears to exist for the ESB to incorporate additional operational rules based on rainfall forecast and/or measurement thresholds. These rules could operate for the reservoir levels below the Maximum Normal Operating Levels and include the lowering of reservoir levels prior to a flood event. Such rules will be constrained by limitations on reservoir drawdown rates and reasonable electricity generation interests but could take precedence over seasonal operational rules (such as the covering of the tree stumps in the Gearagh during the summer). The benefit of modifying operational rules will be assessed during the hydraulic modelling stage of the Lee CFRAM Study.


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9. Summary and recommendations

9.1. Summary of key outputs

A detailed hydrological assessment has been undertaken as part of the Lee CFRAMS. Methodologies in the Flood Studies Report and Flood Estimation Handbook have been used to analyse meteorological and hydrometric data to estimate extreme flows in the main rivers and tributaries in the catchment.

The key outputs from this assessment include:

• Study growth curve;

• Study unit hydrograph;

• Index floods for each subcatchment (Qmed);

• Revised rating curves providing higher confidence in high flow estimates for eleven prioritised hydrometric gauges in the catchment;

• Design flows for a range of durations for the 50%, 20%, 10%, 4%, 2%, 1%, 0.5% and 0.1% AEP events for existing conditions for each subcatchment;

• Two future scenarios taking into consideration the mid range and high end of future climate change and land use change predictions;

• Design flows for a range of durations for the 50%, 20%, 10%, 4%, 2%, 1%, 0.5% and 0.1% AEP events for the MRFS and 1%, 0.5% and 0.1% AEP events for the HEFS for each subcatchment.

The outputs from the hydrological assessment will be used in the hydraulic modelling and flood risk management option assessment stages of the Lee CFRAMS.

9.2. Recommendations

While there is extensive meteorological and hydrometric data available in the Lee catchment, there have been difficulties in obtaining digitised data and digitising large amounts of paper charts was not possible within the timescales of this study. It is recommended that the full data record is digitised to enable further analysis options to future reviews of the Lee CFRAMS hydrology, including peak over threshold statistical analysis and unit hydrograph analysis. It is also recommended that a joint ESB, EPA and OPW review is undertaken to ascertain whether further collaboration is possible in accessing, storing and disseminating data from ESB gauges.

In order to improve the coverage of meteorological; data in the catchment it is recommended that two additional rainfall gauges are located in the Owenacurra catchment, one at the base of the valley 1km North of Middleton, and another on a high spur between the Owenncurra and Leamlarra Rivers. In addition, hydrometric gauges on the Tramore, Curragheen, Glasheen, Bride (north of Lee) and Dungourney rivers are recommended. Section 6.2.2 recommends that an additional (possibly temporary) hydrometric gauge is placed on the Owenboy River to assist in future reviews of the catchment runoff characteristics.


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Given the rainfall under prediction identified in the FSR rainfall mapping, as detailed in Section 5.3, it is recommended that the City and County Councils consider the use of the Lee CFRAMS M5-2Day contours or preliminary FSU outputs for surface water drainage design within the study area or increase FSR M5-2Day values by 20%. It is also recommended that the Lee CFRAMS annual maximum rainfall values are reviewed on an annual basis (Section

5.4). If this review identifies a sustained increase in long term annual maximum rainfall trends, it is recommended that the index rainfall is increased throughout the study area. It also recommended that future reviews of the Lee CFRMP consider the rainfall data from the six ESB rain gauges in the catchment.

A review of the rating curves at eleven prioritised hydrometric stations was undertaken to maximise the accuracy of extreme flows estimates within the scope of the methodologies and data available. Rating reviews of the remaining ten gauges as part of the review of the Lee CFRMP will assist in further increasing the potential accuracy of the lower priority hydrometric gauges in the study area. As detailed in Section 2.2.3, it is also recommended that rating curves developed using the HRSC data are revised at a future date to include floodplain details generated from LiDAR data.

This report acknowledges that an unresolved apparent discrepancy may exist at the 19001 gauge (Section 6.2.2). It is recommended that the OPW consider the installation of a temporary recorder nearby on the Owenboy to facilitate confirmation of recorded flood flows in subsequent revisions of the Lee CFRMP. The rating curve review identified that there is limited high flow spot gauge measurements at the gauging stations. We would recommend that where possible additional spot gaugings be recorded at higher flows. At gauge 19012 there is limited spot gaugings post 1990 when channel works had taken place. We would recommend that additional spot gaugings are recoded at this gauging location.

In addition to determining the existing flood risk, there are a number of drivers that can influence future flood risk in the Lee catchment, including climate change, afforestation and urbanisation. In relation to climate change and net sea level rise, it is recommended that subsequent revisions of the Lee CFRMP consider data available from a CGPS station at Castletownbere (Section 8.2.3) in assessing isostatic subsidence along the south coast of Ireland.

To facilitate the assessment of potential future flood risk, two future flood risk management scenarios have been proposed, a Mid Range Future Scenario and a High End Future Scenario. The range of parameters incorporated in each of the future scenarios has been determined from a comprehensive review of current research. The first report on results from the UKCIP08 Climate Emissions study is due to be published late 2007 and it is recommended that the outcome of this study be consulted to inform future catchment studies.

In the UK, Defra are currently undertaking a study with CIRIA on the effectiveness of SUDS (Section 8.7.1). There is a growing view that SUDS may not be as effective/value for money as postulated and other mitigation measures may be more cost effective. It is recommended that the findings of this study are reviewed and considered in future revisions of the Lee CFRMP.

Due to the inherent uncertainty associated with hydrological estimates confidence limits have been derived to reduce the uncertainty associated with the estimates. Use of the confidence limits will be dependent on the application. For the Lee CFRAMS the design estimates are to be used without confidence limits applied for the hydraulic modelling and flood mapping of the existing case with the confidence limits providing a sensitivity test when determining


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appropriate freeboard. When designing for the future scenarios the appropriate confidence limit should be applied to the design flow.

For applications outside of the Lee study, where inclusion of the 95%ile confidence limit is required in flood estimates (for example, Section 50 applications), it is recommended that design flows provided in this study are scaled by an average factor of 1.52.

The ESB play a significant flood management role in the Lee catchment through the operation of the hydroelectric dams at Carrigadrohid and Inishcarra. A preliminary assessment of the impact of their operations on the catchment has been made as part of the hydrological assessment and it is recommended that further consultation with the ESB is undertaken during the hydraulic modelling and flood risk management options stages of this study.


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Appendices


Hydrology Report

A1

Appendix A. Data collection


Hydrology Report

A2

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Hydrology Report

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ca Q

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Dig

ital

Pau

l Dun

ne17

/10/

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ca Q

uinn

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l Dun

ne21

/10/

06

105

NH

ydro

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EP

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atin

g cu

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ions

190

36, 1

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23/1

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106

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Hyd

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gene

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20m

D

EM

and

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GIS

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in P

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GL)

YG

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ata

Dig

ital

Pau

l Dun

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/10/

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ne23

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113

NH

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Com

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Max

ann

ual f

low

dat

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en

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Tom

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07/1

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08/1

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188

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sum

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ents

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ital

Pau

l Dun

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/01/

07

236

NH

ydro

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hydr

omet

ric d

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for

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or g

auge

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Dig

ital

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l Dun

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ca Q

uinn

Pau

l Dun

ne28

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07

237

NH

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nn (

EP

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YS

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ets

Dig

ital

Pau

l Dun

ne27

/03/

07R

ebec

ca Q

uinn

Pau

l Dun

ne28

/03/

07

239

NH

ydro

logy

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t gau

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for

the

follo

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drom

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ges

1900

1P

eter

New

port

(O

PW

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Spr

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heet

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igita

lP

aul D

unne

27/0

3/07

Pet

er N

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rtP

aul D

unne

03/0

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249

NH

ydro

logy

Wat

er L

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dat

a fo

r th

e E

SB

st

atio

ns fr

om 2

002

to 2

005

John

Mar

tin (

OP

W)

YS

prea

dshe

ets

Dig

ital

Pau

l Dun

ne11

/04/

07M

ark

Ada

mso

nP

aul D

unne

13/0

4/07

252

NH

ydro

logy

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t gau

ge d

ata

from

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ES

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Doc

umen

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30/0

3/07

Mar

k A

dam

son

Pau

l Dun

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Hydrology Report

A4

Sor

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Dat

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Dig

ital

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l Dun

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ark

Ada

mso

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NH

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Pet

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to

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Reb

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EP

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YS

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Dig

ital

Pau

l Dun

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/05/

07R

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ca Q

uinn

Pau

l Dun

ne15

/05/

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322

NH

ydro

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rt d

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15/0

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k A

dam

son

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l Dun

ne18

/07/

07

328

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rai

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l dat

a. 5

yr -

1hr

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GIS

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ital

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330

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ibra

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Dig

ital

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ark

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ents

Dig

ital

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Hem

sley

26/0

7/07

343

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th

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Dig

ital

--

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14/0

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344

NH

ydro

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det

ailin

g co

mm

ents

fr

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hyd

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etric

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in

rela

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14/0

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Dig

ital

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07

354

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Dig

ital

Pau

l Dun

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07R

ebec

ca Q

uinn

Pau

l Dun

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/10/

07

357

NH

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ital

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l Dun

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07M

ark

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Hydrology Report

A5

A2 Data from the flood hazard mapping website

Sor

t by

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alcr

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by

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rec

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51N

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ts fr

om

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t on

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ork

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-

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ary

1996

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appi

ng

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M)

web

site

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ww

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06

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ork

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web

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ng.i

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cum

ent

--

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lare

Dew

ar03

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06

53N

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ts fr

om

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om P

addy

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lare

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06

54N

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06

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06

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06

58N

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06

59N

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06

60N

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lare

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06

61N

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lare

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06

62N

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ts fr

om

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--

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lare

Dew

ar03

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06

63N

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lare

Dew

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06

64N

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--

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lare

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06


Hydrology Report

A6 S

ort b

y D

ata_

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befo

re e

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ing

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dat

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Des

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tion

Ent

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satio

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fills

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crow

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son

that

dat

a is

sen

t to

Data

_ID

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pers

ed

ed

Cate

go

ryN

am

e o

f d

ata

ite

mD

ata

av

aila

ble

fro

mw

ith

Ha

lcro

w a

nd

su

b c

on

su

lta

nts

?T

yp

e o

f d

ata

Req

ueste

d b

yD

ate

req

ueste

dR

eq

uest

se

nt

toR

ec

eiv

ed

by

Date

rec

eiv

ed

66N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

te

New

spap

er a

rtic

le fr

om th

e Ir

ish

Exa

min

er fr

om A

ugus

t 198

7 re

latin

g tp

floo

d co

ntro

l fro

m In

ishc

arra

dam

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

YN

ewsp

aper

ar

ticle

--

-C

lare

Dew

ar03

/10/

06

67N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teE

veni

ng E

cho

New

spap

er a

rtic

le

from

6.0

8.19

86 -

floo

ding

in C

ork

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

YN

ewsp

aper

ar

ticle

--

-C

lare

Dew

ar03

/10/

06

68N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

te

Lee

flood

con

trol

and

Dam

saf

ety

- su

ppor

t doc

umen

t on

Flo

od F

orec

ast

mod

ellin

g fo

r C

ork

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-C

lare

Dew

ar03

/10/

06

69N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teF

lood

War

ning

Sys

tem

s in

Cor

k C

ount

y

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-C

lare

Dew

ar03

/10/

06

70N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teLe

tter

rega

rdin

g flo

odin

g at

S

enan

dale

Clo

ghro

e

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-C

lare

Dew

ar03

/10/

06

71N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teR

epor

t on

the

Flo

odin

g Le

vels

from

F

ebru

ary

2002

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-C

lare

Dew

ar03

/10/

06

72N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teF

lood

ext

ent m

aps

for

the

Low

er L

ee

for

the

Aug

ust 1

986

Flo

od E

xten

t

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

YM

ap-

--

Cla

re D

ewar

03/1

0/06

73N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teR

epor

t on

the

Nov

embe

r 20

0o fl

ood

on th

e R

iver

Lee

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-C

lare

Dew

ar03

/10/

06

74N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teM

et E

irean

n m

ontly

wea

ther

bul

letin

-

Aug

ust 1

986

stor

m

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-C

lare

Dew

ar03

/10/

06

75N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teF

lood

ing

in th

e M

unst

er B

lack

wat

er

Cat

chm

ent 6

Aug

ust 8

6.pd

f

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-C

lare

Dew

ar03

/10/

06


Hydrology Report

A7

Sor

t by

Dat

a_ID

be

fore

ent

erin

g a

new

dat

a ite

m

Has

dat

a be

en

supe

rsed

ed?

Des

crip

tion

Ent

er p

erso

n an

d or

gani

satio

nT

his

fills

in

auto

mat

ical

ly

Dra

win

g /

Doc

umen

t /

Pho

to /

GIS

etc

.H

alcr

ow p

erso

nO

PW

/ ot

her

orga

nisa

tion/

per

son

Hal

crow

per

son

that

dat

a is

sen

t to

Data

_ID

Su

pers

ed

ed

Cate

go

ryN

am

e o

f d

ata

ite

mD

ata

av

aila

ble

fro

mw

ith

Ha

lcro

w a

nd

su

b c

on

su

lta

nts

?T

yp

e o

f d

ata

Req

ueste

d b

yD

ate

req

ueste

dR

eq

uest

se

nt

toR

ec

eiv

ed

by

Date

rec

eiv

ed

76N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teO

verv

iew

of M

unst

er F

lood

Aug

ust

1986

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-C

lare

Dew

ar03

/10/

06

77N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teR

epor

t on

the

Riv

er L

ee F

lood

5&

6 A

ugus

t 198

6

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-C

lare

Dew

ar03

/10/

06

78N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teR

epor

t on

the

Riv

er L

ee F

lood

F

ebru

ary

1997

.pdf

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-C

lare

Dew

ar03

/10/

06

87N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teN

ewsp

aper

Art

icle

from

the

Eve

ning

E

ch N

ewsp

aper

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

YN

ewsp

aper

ar

ticle

--

-Li

nda

Hem

sley

13/1

0/06

88N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teN

ewsp

aper

Art

icle

from

the

Exa

min

er

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

YN

ewsp

aper

ar

ticle

--

-Li

nda

Hem

sley

13/1

0/06

89N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teN

ewsp

aper

Art

icle

from

Inde

pend

ent

Pre

ss

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

YN

ewsp

aper

ar

ticle

--

-Li

nda

Hem

sley

13/1

0/06

90N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teN

ewsp

aper

Art

icle

from

the

Iris

h T

imes

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

YN

ewsp

aper

ar

ticle

--

-Li

nda

Hem

sley

13/1

0/06

91N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teN

ewsp

aper

Art

icle

from

the

Iris

h T

imes

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

YN

ewsp

aper

ar

ticle

--

-Li

nda

Hem

sley

13/1

0/06

92N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teP

hoto

s of

floo

ding

from

Bal

lyga

rven

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Yph

otos

--

-Li

nda

Hem

sley

13/1

0/06

93N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teP

hoto

s of

floo

ding

from

Car

raga

line

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Yph

otos

--

-Li

nda

Hem

sley

13/1

0/06

94N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teF

lood

ing

repo

rt -

Car

raga

line

Cro

ssha

ven

Roa

d -

Nov

embe

r 20

04

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

YD

ocum

ent

--

-Li

nda

Hem

sley

13/1

0/06

95N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teF

lood

ing

repo

rt -

Car

raga

line

- N

ovem

ber

2002

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

YD

ocum

ent

--

-Li

nda

Hem

sley

13/1

0/06


Hydrology Report

A8

Sor

t by

Dat

a_ID

be

fore

ent

erin

g a

new

dat

a ite

m

Has

dat

a be

en

supe

rsed

ed?

Des

crip

tion

Ent

er p

erso

n an

d or

gani

satio

nT

his

fills

in

auto

mat

ical

ly

Dra

win

g /

Doc

umen

t /

Pho

to /

GIS

etc

.H

alcr

ow p

erso

nO

PW

/ ot

her

orga

nisa

tion/

per

son

Hal

crow

per

son

that

dat

a is

sen

t to

Data

_ID

Su

pers

ed

ed

Cate

go

ryN

am

e o

f d

ata

ite

mD

ata

av

aila

ble

fro

mw

ith

Ha

lcro

w a

nd

su

b c

on

su

lta

nts

?T

yp

e o

f d

ata

Req

ueste

d b

yD

ate

req

ueste

dR

eq

uest

se

nt

toR

ec

eiv

ed

by

Date

rec

eiv

ed

96N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teP

hoto

s of

floo

ding

from

Car

raga

line

- Ja

nuar

y 20

05 a

nd N

ovem

ber

2002

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Yph

otos

--

-Li

nda

Hem

sley

13/1

0/06

97N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teP

hoto

s of

floo

ding

from

Car

ralin

e fr

om N

ovem

ber

1994

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Yph

otos

--

-Li

nda

Hem

sley

13/1

0/06

98N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teP

hoto

s of

floo

ding

from

Dou

glas

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Yph

otos

--

-Li

nda

Hem

sley

13/1

0/06

99N

Flo

odin

g R

epor

ts fr

om

FH

M w

ebsi

teP

hoto

s of

floo

ding

from

Wat

er R

ock

in M

idel

eton

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-Li

nda

Hem

sley

13/1

0/06

100

NF

lood

ing

Rep

orts

from

F

HM

web

site

Doc

umen

t of r

ecor

ded

flood

ing

com

plai

nts

for

the

1988

floo

d ev

ent

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-Li

nda

Hem

sley

13/1

0/06

101

NF

lood

ing

Rep

orts

from

F

HM

web

site

Kiln

arle

ry fl

ood

stud

y

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-Li

nda

Hem

sley

13/1

0/06

102

NF

lood

ing

Rep

orts

from

F

HM

web

site

Rep

ort o

n th

e N

ovem

ber

2000

floo

d -

Cou

nty

Cor

k S

outh

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Ydo

cum

ent

--

-Li

nda

Hem

sley

13/1

0/06

103

NF

lood

ing

Rep

orts

from

F

HM

web

site

Pho

tos

of c

oast

al fl

oodi

ng a

t R

inga

bella

Flo

od H

azar

d M

appi

ng

(FH

M)

web

site

w

ww

.floo

dhaz

ardm

appi

ng.i

e

Yph

otos

--

-Li

nda

Hem

sley

13/1

0/06


Hydrology Report

A9

A3 Mapping data

So

rt b

y D

ata

_ID

be

fore

ent

erin

g a

ne

w d

ata

item

Has

dat

a b

een

su

per

sed

ed?

De

scri

ptio

nE

nte

r p

erso

n a

nd

orga

nisa

tion

Thi

s fil

ls in

a

uto

mat

ical

ly

Dra

win

g /

Do

cum

ent /

P

hoto

/ G

IS e

tc.

Hal

crow

pe

rson

OP

W /

oth

er

orga

nis

atio

n/ p

ers

onH

alcr

ow p

erso

n

tha

t da

ta is

sen

t to

Data

_ID

Su

pers

ed

ed

Cate

go

ryN

am

e o

f d

ata

ite

mD

ata

av

aila

ble

fro

mw

ith

Ha

lcro

w a

nd

su

b c

on

su

lta

nts

?T

yp

e o

f d

ata

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ueste

d b

yD

ate

req

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dR

eq

uest

se

nt

toR

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eiv

ed

by

Date

rec

eiv

ed

13

YM

app

ing

Dis

cove

ry s

erie

s 50

000

sca

le r

aste

r m

aps

John

Mar

tin (

OP

W)

YG

IS d

ata

Cla

re D

ewar

Joh

n M

artin

Cla

re D

ew

ar

06/0

9/0

6

14

NM

app

ing

6 in

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Sca

le R

ast

er

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sJo

hn M

artin

(O

PW

)Y

GIS

da

taC

lare

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arJo

hn

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wa

r06

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06

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app

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0 s

cale

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cto

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hn M

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da

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aul

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ne08

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06

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n M

artin

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/09/

06

16

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app

ing

5000

0 s

cale

con

tour

dxf

file

sJo

hn M

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da

ta-

--

P D

unn

e12

/09/

06

21

NM

app

ing

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0 tf

w f

iles

John

Mar

tin (

OP

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YG

IS d

ata

Pa

ul D

unne

11/

09/

096

Joh

n M

artin

P D

unn

e15

/09/

06

22

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app

ing

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cove

ry s

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s 50

000

sca

le

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aps

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hn M

artin

(O

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da

ta-

--

P D

unn

e15

/09/

06

30

NM

app

ing

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pef

ile o

f th

e C

ork

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Mai

n D

rain

age

sys

tem

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en D

oyle

YG

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ata

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re D

ewar

15/0

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on W

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Hydrology Report

A10

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Hydrology Report

A11

A4 Data status tables

Hydrometric Data Frequency

Station Name

Station

ID 1877… 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Station ID Provider

Ballea 19001 19001 OPW

Buckley's Bridge 19005 19005 EPA

Glanmire 19006 19006 EPA

Brookhill 19009 19009 EPA

Upstream Leemount Bridge 19011 19011 ESB

Downstream Leemount Bridge 19012 19012 ESB

Inniscarra 19013 19013 ESB

Dromcarra 19014 19014 ESB

Healy's Bridge 19015 19015 ESB

Oven's Bridge 19016 19016 ESB

Bawnnafinny 19017 19017 EPA

Tower 19018 19018 EPA

Ballyedmond 19020 19020 EPA

East Cork Foods 19022 19022 EPA

Shanakill 19027 15 Minute Maximum Annual Flows 19027 ESB

Dripsey Woollen Mills 19028 Peak Daily 19028 ESB

Macroom 19031 19031 ESB

Meadowbrook 19032 19032 EPA

Kilmona 19044 19044 OPW

Gothic 19045 19045 OPW

Station Road 19046 19046 OPW

KEY

Meteorological Data Frequency

Station Name

Station

ID 1877… 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Station ID Provider

Roche's Point 1004 1004 Met Eireann

Roche's Point 2 1004-2 1004-2 Met Eireann

Rathduff G.S. 1504 1504 Met Eireann

Coomclogh Daily 1901 1901 Met Eireann

Ballyvourney (Clountycarty) 2604 2604 Met Eireann

Gouganebarra Daily 2704 2704 Met Eireann

Donoughmore Daily 2804 2804 Met Eireann

Ballinagree (Mushera) 2904 2904 Met Eireann

Ballingeary (Voc.Sch.) 3004 3004 Met Eireann

Carrigadrohid (Gen.Stn.) 3604 3604 Met Eireann

Inishcarra (Gen.Stn.) 3704 3704 Met Eireann

Macroom (Renanirree) 3804 3804 Met Eireann

Youghal (St.Raphael's 3806 3806 Met Eireann

Cork Airport 3904 3904 Met Eireann

Ballineen Daily 4002 4002 Met Eireann

Ballintrideen Daily 4402 4402 Met Eireann

Ballymacoda (Mountcotton) 4404 4404 Met Eireann

Ballineen (Carbery) 4602 4602 Met Eireann

Dungourney (Ballyeightragh) 4804 4804 Met Eireann

Killeagh (Monabraher) 4904 4904 Met Eireann

Shanagarry North 5004 5004 Met Eireann

Macroom (Curraleigh) 5204 5204 Met Eireann

Dunmanway (Keelaraheen) 5302 5302 Met Eireann

Cork Montenotte 5404 5404 Met Eireann

Cork (Douglas) 5504 5504 Met Eireann

Aherlamore Daily 5704 5704 Met Eireann

Watergrasshill (Tinageragh) 5804 1 Hour Data Not Awaiting 5804 Met Eireann

Muskerry (Golf 6104 Daily 6104 Met Eireann

Lombardstown (Drompeach) 6206 6206 Met Eireann

Banteer Lyre 6306 6306 Met Eireann

Coolea (Milleens) 6404 6404 Met Eireann

Little Island 6504 6504 Met Eireann

Fota Island 6604 6604 Met Eireann

Castlemartyr (Killamucky) 6704 6704 Met Eireann

Bartlemy Daily 7006 7006 Met Eireann

OPW Station 80701 80701 OPW








KEY


Hydrology Report

B1

Appendix B. Historical flood events


Hydrology Report

B2


Hydrology Report

B3


Hydrology Report

B4


Hydrology Report

B5


Hydrology Report

B6


Hydrology Report

B7


Hydrology Report

C1

Appendix C. Meteorological analysis


Hydrology Report

C2

C1 2 Day rainfall quartile analysis

C1.1 Overview

This appendix provides details of the meteorological analysis undertaken, supplementing the information provided in Section 5 of the report. Information on the available rainfall data is described in Section 2.4.

Table C1 outlines the notation referred to throughout Appendix C.

Table C1 Notation

Notation Explanation

AMfixed-1hr annual maximum 1 hour rainfall for fixed duration (calendar hour)

(note that sometimes 'fixed' notation is dropped for ease)

RMEDfixed-1hr median value from annual maxima series of 1 hour rainfall


AMfixed-2day annual maximum 2 day rainfall for fixed duration (calendar days)


RMEDfixed-2day median value from annual maxima series of 2 day rainfall


N number of years of record (or number of annual maxima)

F(i) Gringorton plotting position value interims of its ith position

y Gumbel reduced variate value

T return period in years

QM1 mean of the first quartile of a series of annual maxima

(similarly QM2, QM3 and QM4 are the second, third and fourth quartile means)

M middle half mean of the middle half i.e. mean of QM2 and QM3

M upper half mean of the upper half i.e. mean of QM3 and QM4

2M, 1M, M2, M5, …, MT the value with return period 1/2, 1, 2, 5, …, T years


Hydrology Report

C3

H1 the highest value of a series of annual maxima

(similarly H2, H3 and H4 are the second, third and fourth highest values)

R the ratio of 60 minute M5/2 day M5

X extreme value of rainfall

C1.2 2 Day annual maxima

The analysis of 2-Day annual maxima was based on the FSR Section 2.2 (Graphical analysis of a set of annual maxima).

Each gauged record set of 2-day annual maxima with N annual maxima was ranked into ascending order and RMEDfixed-2day calculated. The plotting position and reduced variate y were obtained using the Gringorton plotting position and the Gumbel reduced variate (equations 8.1 and 8.2 respectively from FEH).

Gringorton Plotting Position Formulae: F(i) = (i - 0.44) / (N + 0.12)

F(i) is the non-exceedance probability, i the rank in ascending order

Gumbel Reduced Variate Formulae: y = -ln (-lnF)

Standardised values of rainfall (AMfixed-2day / RMEDfixed-2day) versus were produced at each gauge and compiled together in Figure C1. The averaged rainfall growth curve can be seen tending towards 1.9-1.8 times the median annual rainfall for the 1 in 100 year storm event. This tendency is slightly below the corresponding hydrology growth curve factor, but broadly consistent with trends. Section 6.5.2 provides further discussion on the relationship between the meteorological and hydrological growth curves.

100010050201052

0.0

0.5

1.0

1.5

2.0

2.5

3.0

-2 -1 0 1 2 3 4 5 6 7

Reduced variate, y

Sta

nd

ard

ise

d 2

Da

y R

ain

fall

Return Period

Figure C1 2 day duration rainfall data plotted using the Gumbel plotting positions


Hydrology Report

C4

C1.3 Annual maxima quartile analysis

A quartile analysis (FSR Volume II Section 2.2) was completed of the 2-day annual maxima rainfall data. The analysis involved the following steps:

1. At each station the ordered annual maxima were divided into four quartiles. This was achieved by notionally taking each annual maxima value four times, giving a total of 4 x N values.

2. The quartile geometric means (QM1, QM2, QM3 and QM4) were calculated. (Geometric mean preferable as rainfall data tends to show proportional increases).

3. The geometric mean of the middle half and the upper half i.e. geometric mean of QM2 & QM3 and QM3 & QM4 respectively were also calculated.

The four highest values H4, H3, H2 and H1 were noted.

4. The quartile geometric means above may be shown to correspond to theoretical values (Jenkinson, 1974) for the reduced variate y shown in the summary table below. The quartile means also show a close relationship to yearly return (Table C2).

Table C2 Quartile summary for 2 day annual maximum rainfall (From FSR Volume II)

Quartile Parameter Return Period (years) Reduced Variate (y)

QM1 2M -0.8

QM2 1M 0.02

QM3 0.77

QM4 M10 2.32

Middle half M2 0.4

Upper half M5 1.55

H4

H3

H2

H1

The Return Period and reduced variate for H1, H2, H3 and H4 are calculated from the corresponding annual maxima value.


Hydrology Report

C5

C1.4 Graphical plotting of M5-2day rainfall

Following the quartile summary and calculating of M5, A multiplication factor of 1.11 was used to convert the M5-2day point values at each station from calendar fixed duration 2 day values to sliding duration 48 hour values (FSR Section 3 and FEH Section 10). The FEH multiplication factor (Table 10.1) was considered a better estimate than that contained within the FSR as this document is the latest standard.

The M5-2day point values were now plotted onto a catchment map at the geographical station positions. Taking account of catchment topography a set of isohyetal lines were plotted and the FSR M5-2day isohyetal lines superimposed so comparison could be made.

C1.5 Combination of data sets – Study growth curves

In accordance with FSR methodology a regional set of growth curves were compiled for the study area with several classes. The sets of annual maxima and their corresponding quartile summaries were classed according to the magnitude of their M5 value (five year return period value). The ranges taken for each class were similar to those used within the FSR analysis i.e. 60-75mm, 75-100mm and 100-150mm so that comparison could be made. Effectively this incorporated all of the useable data sets.

For each class division the quartile parameters were set out for all of the gauges from the quartile summaries along with the values of N and H1/M2 calculated at each gauge. See example below of column headings for quartile analysis parameters:

_________________________________________________________________

N QM1 QM2 QM3 QM4 Middle Upper H4 H3 H2 H1

H1/M2

half half

2M 1M M10 M2 M5

_________________________________________________________________

The median value (mean of the middle half in a quartile analysis) was obtained for each of the above column headings (quartile analysis parameters). This gave a table of median values for each class with which to generate a growth curve.

In order to extend the growth curves a full quartile summary was undertaken for the values of H1 (extreme value of point rainfall for each data set) for each class. And a full quartile summary made for this, with standardised values (using M5 value) of H1 taken.

However due to the spatial positioning of the network of stations used and the relatively small data sets the extreme H value analysis was not used to further extend the growth curve. Instead the FSR growth curve factors (Table 2.7 and 2.9) were used to extend beyond the M50-2day. Growth factors from Table 2.9 from Scotland and Northern Ireland were chosen as they appeared a better fit of the two.

C1.6 Plotting comments

65-70mm: Scot/NI distribution appears to be a closer fit. Used all points from quartile and H1 analysis. 12 stations with 44 year average i.e. N=522. Used Scot/NI growth factors from M1000 up to fit to long term trend. Polynomial order 3 used as trend line.


Hydrology Report

C6

70-100mm: H1 analysis values at the top end tend to be of poor quality. Possibly due to poor average length of record. Upper quartile and extreme values do not compare closely with that of FSR growth curves. Disregard H1 quartile analysis, and use Scot/NI distribution as it appears to fit better at higher return periods. 15 stations with 21 year average. N=315. Used Scot/NI growth factors from M100 up to fit to long term trend. Polynomial order 3 used as trend line.

100-150mm: Scot/NI growth curve used as both FSR growth curves are very similar. 2 stations at 58 year average. Used Scot/NI growth factors from M1000 up to fit to long term trend. Polynomial order 3 used as trend line.

C1.7 2 Day quartile analysis results

Results from the quartile analysis are provided in tabular form (Table C3). The implications of the quartile analysis are discussed further in Section 5.2.

The primary deliverables from the 2 day rainfall analysis are the rainfall growth curves (Figures 5.1 to 5.3 in Section 5) and the M5-2Day rainfall plots (Figure C5)


Hydrology Report

C7

Table C3 2 Day duration quartile analysis results

Ranked fixed sliding 2M 1M M10 M2 M5

Station M5-2day M5-2day QM1 QM2 QM3 QM4 M mid. Half M up. Half H4 H3 H2 H1 H1/M2

Class 60-75mm 5004 59.6 66.1 34.01 44.02 51.88 68.38 47.79 59.56 67.00 70.00 75.00 85.00 1.78

3806 61.9 68.7 35.99 45.86 52.75 72.62 49.18 61.89 75.00 79.00 80.00 134.00 2.72

1004 62.1 68.9 34.66 44.39 54.36 70.93 49.12 62.09 78.00 79.80 84.40 94.40 1.92

4404 63.7 70.7 34.69 43.25 54.13 74.98 48.39 63.71 71.00 80.00 90.00 103.00 2.13

3704 67.7 75.2 40.76 49.80 58.93 77.79 54.18 67.71 82.00 83.00 87.00 100.00 1.85

5404 69.6 77.3 36.91 53.19 63.43 76.43 58.08 69.63 70.00 72.00 87.00 97.00 1.67

3604 70.6 78.4 45.83 53.75 61.63 80.96 57.55 70.64 91.00 92.00 97.00 109.00 1.89

7006 71.2 79.1 28.39 53.21 63.08 80.46 57.94 71.25 66.00 77.00 83.00 90.00 1.55

1504 72.8 80.8 39.15 50.57 61.83 85.81 55.92 72.84 101.00 101.00 109.00 155.00 2.77

2804 73.2 81.3 45.74 56.26 65.97 81.26 60.92 73.22 84.00 91.00 93.00 102.00 1.67

4904 84.0 93.2 42.10 51.24 61.37 87.60 56.08 73.32 84.00 88.00 100.00 103.00 1.84

3904 74.5 82.7 43.20 55.02 66.22 83.86 60.36 74.52 84.00 91.00 96.00 122.00 2.02

Class 75-100mm 6306 75.8 84.1 50.15 58.36 65.60 87.52 61.88 75.77 86.00 92.00 95.00 97.00 1.57

4804 76.3 84.7 40.82 53.31 67.93 85.78 60.18 76.33 84.00 87.00 102.00 102.00 1.70

4402 76.4 84.8 43.89 53.34 66.73 87.38 59.66 76.36 66.20 79.30 88.50 92.80 1.56

6104 76.4 84.8 50.81 58.23 69.55 83.85 63.64 76.36 75.20 76.70 83.60 89.90 1.41

5504 76.4 84.8 42.99 57.70 65.95 88.59 61.68 76.43 76.00 90.00 103.00 113.00 1.83

5704 76.8 85.3 49.30 57.09 66.70 88.52 61.71 76.84 85.00 87.00 95.00 112.00 1.81

4602 77.2 85.6 58.43 64.55 71.65 83.09 68.01 77.16 73.00 80.70 81.10 87.00 1.28

6206 79.2 87.9 46.95 60.58 71.76 87.46 65.93 79.22 86.00 88.00 91.00 91.00 1.38

4002 79.3 88.0 50.46 61.83 69.61 90.25 65.61 79.26 90.00 91.00 94.00 96.00 1.46

2904 79.3 88.0 45.14 57.63 69.56 90.44 63.32 79.32 99.00 99.00 106.00 113.00 1.78

2604 79.6 88.3 51.98 61.38 68.99 91.77 65.07 79.57 96.00 112.00 121.00 121.00 1.86

5804 79.7 88.4 46.57 62.95 68.09 93.25 65.47 79.68 90.00 94.00 100.00 101.00 1.54

5204 82.1 91.1 55.45 65.99 73.35 91.89 69.57 82.10 93.00 94.00 100.00 104.00 1.49

3804 85.6 95.0 53.39 61.70 74.05 98.85 67.59 85.55 106.00 111.00 117.00 122.00 1.80

1901 93.1 103.3 72.16 78.37 84.25 102.83 81.26 93.08 89.70 89.90 101.50 123.30 1.52

Class 100-150mm 3004 110.2 122.4 67.21 81.73 97.14 125.11 89.10 110.24 135.00 146.00 162.00 167.00 1.87

2704 123.6 137.2 85.86 97.46 107.43 142.31 102.32 123.65 159.00 159.00 162.00 205.00 2.00

Note: Station 5004 M5-2day value falls into Class 60-75mm when considered to 2 significant figures

Full Quartile Summary of H1 and stabilised H1/M5 values

Class 60-75mm

N 44 Note : N value taken from Class Quartile Analysis

522

Quartile Return Period Stabilised Standardised Red. Variate Red. Variate

Parameter T H1 (mm) H1/M5 H1 (mm) y (N=44) y (N=522)

QM1 89.80 1.30 89.94

QM2 N = 44 99.67 1.45 100.20 3.77

QM3 105.00 1.55 107.18

QM4 9.5N = 418 137.00 2.02 139.97 6.03

M middle half 1.45N = 64 102.33 1.50 103.69 4.15

M upper half 4.5N = 198 121.00 1.78 123.57 5.29

H4 109.00 1.61 111.37 4.99

H3 122.00 1.69 117.16 5.32

H2 134.00 2.17 150.11 5.81

H1 155.00 2.20 152.63 6.84

Equivalent Table 2.5 in FSR II Met. Studies Plotting Positions


Class 75-100mm


315



QM1 90.00 1.13 88.37

QM2 N = 21 98.19 1.25 97.45 3.02

QM3 110.16 1.39 109.08

QM4 9.5N = 200 122.20 1.51 117.84 5.29

M middle half 1.45N = 30 104.63 1.33 103.67 3.40

M upper half 4.5N = 95 114.35 1.43 112.08 4.54

H4 113.00 1.48 115.76 4.48

H3 121.00 1.49 116.37 4.81

H2 122.00 1.50 117.52 5.31

H1 123.30 1.52 119.27 6.33



Class 100-150mm


116



QM1 167.00 1.52 178.22

QM2 N = 58 167.00 1.52 178.22 4.05

QM3 205.00 1.63 190.69

QM4 9.5N = 551 205.00 1.63 190.69 6.31

M middle half 1.45N = 84 185.03 1.58 184.35 4.43

M upper half 4.5N = 261 205.00 1.63 190.69 5.56

H4 - - - 3.48

H3 - - - 3.81

H2 167.00 1.52 178.22 4.31

H1 205.00 1.63 190.69 5.33



Hydrology Report

C9

C2 1 Hour rainfall quartile analysis

C2.1 Methodology

The 1 hour quartile analysis closely followed the 2 day analysis presented in Appendix C1. The primary difference in the analysis was that a fixed duration rebase factor of 1.16 was used in accordance with FEH Vol2 Table 10.1.

C2.2 1 hour annual maximum

1 hour rainfall data was only available at two rain gauges in the South East of the study area: Roches Point and Cork Airport. Both gauges tend to slightly higher growth factors (approximately 2.1 - 2.3 times the median annual rainfall compared with 1.8 - 1.9 for the 2 day duration) than the study averaged 2 day (Figures C2 and C3). This tendency of shorter durations producing steeper growth curves is not explicitly acknowledged in the FSR, but is apparent in the data contained in FSR Vol 2 Table 3.4.

2 5 10 20 50 100 1000

0.0

0.5

1.0

1.5

2.0

2.5

-2.0 0.0 2.0 4.0 6.0 8.0

Gumbel Reduced Variate y

AM-1hr/Rmed-1hr

Return Period

Figure C2 1004 - Roches Point synoptic station Gringorton plotting positions


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C10

2 5 10 20 50 100 1000

0.0

0.5

1.0

1.5

2.0

2.5

-2.0 0.0 2.0 4.0 6.0 8.0

Gumbel Reduced Variate y

AM-1hr/Rmed-1hr

Return Period

Figure C3. 3904 - Cork Airport synoptic station Gringorten plotting positions

Tables C4 and C5 present the Quartiles results for the Roches Point and Cork Airport Synoptic stations. The primary deliverables from the 1 hr data analysis is the Jenkinson’s Ratio (Table C6 and Figure C6), used to determine the derive design rainfall depths for alternative storm durations.

Table C4 Roches Point quartile analysis results

QUARTILE ANALYSIS RESULTS SUMMARY

stn 1004

N 34

Quartile

Parameter

Return

Period Red. Variate

T y

QM1 2M 0.7 -0.08

QM2 1M 0.9 0.02

QM3 12.2 0.77

QM4 M10 16.8 2.32

M middle half M2 3.3 0.4

M upper half M5 14.3 1.55

H4 15.7 2.2

H3 17.6 2.6

H2 19.9 3.1

H1 24.5 4.1

AMfixed-1hr

x (mm)


Hydrology Report

C11

Table C5 Cork Airport quartile analysis results

QUARTILE ANALYSIS RESULTS SUMMARY

stn 3904

N 42

Quartile

Parameter

Return

Period Red. Variate

T y

QM1 2M 8.5 -0.08

QM2 1M 10.8 0.02

QM3 12.1 0.77

QM4 M10 16.7 2.32M middle

half M2 11.4 0.4

M upper half M5 14.2 1.55

H4 17.2 2.4

H3 18.5 2.8

H2 21.3 3.3

H1 22.6 4.3

AMfixed-1hr

x (mm)

Table C6 Jenkinson’s Ratio

1hr sliding duration rainfall values

Station M5-1hr M5-2day r r as %

1004 16.6 68.9 0.24 24

3904 16.5 82.7 0.20 20

Fixed duration values converted to sliding duration values in accordance with

FEH Volume 2 Section 10.4.1 to allow for discretisation.

See 1 Hr Annual Maximum Series Global Parameters for conversion rebase value.


Hydrology Report

C12

C3 Rainfall drawings

105

kilometres

0

1,000

1,700

1,800

1,900

2,1002,400

1,050

1,100

1,150

1,2001,250

1,300

1,350

1,450

1,550

1,600

950

24/10/2006

© Government of Ireland

OSi Permit Number EN-002-1006

Figure C.4

Lee CFRAMS

Standard Annual Average Rainfall

P:\Y6 Projects\Y6135 - River Lee FRAMS\Civil-CAD

SAAR (mm)

950 to 1,2501,250 to 1,5001,500 to 1,9001,900 to 2,400

Lee Catchment

105

kilometres

0

70

80

85

85

85

80

90

125

100

04/12/2007



Figure C.5

Lee CFRAMS

Index Rainfall (5 year return period, 2 day duration)


M5-2Day (mm)

70 to 8585 to 9090 to 100

100 to 125

Lee Catchment

105

kilometres

0

25

20

25

20

2520

04/12/2007



Figure C.6

Lee CFRAMS

Jenkinson's Ratio (%)(M5-1hr/M5-2Day)


Jenkinson's Ratio (%)

15 to 2525 to 3030 to 30

Lee Catchment


Hydrology Report

D1

Appendix D. Hydrometric analysis


Hydrology Report

D2

D1 Rating curve review

D1.1 Gauge 19001 at Ballea Bridge Upper on the Owenboy River

The gauging station at Ballea Bridge Upper consists of a crump weir located approximately 3m downstream of Ballea Bridge Upper with the staff gauge and recorder house located immediately downstream of the Bridge on the left bank of the channel. The weir is located between the bridge wing walls and has a width of 7.74m and a lowest crest elevation of 8.56mAOD. The Qmed value for the gauge is 17.4 m3/s.

The river channel flows through a narrow valley at the location of the gauge, with an average channel width of approximately 9 meters. The valley extents for 1.2 km upstream of the gauge and for 0.7 km downstream of the gauge. At the downstream extent the valley opens out. The left bank of the channel rises gradually to the R613 road which is approximately 2.7m above the river bed level at the location of the gauge. The R613 flanks the left bank of the Owenboy River for the full length of the valley. From the R613, the valley sides rise steeply and are heavily vegetated. The right bank of the river rises steeply from the bed of the river and is also heavily vegetated. Two structures are located along the study reach; Ballea Bridge Upper and the weir. The river is sinuous in plan form and the gauge is located on a slight bend in the river. The bed slope of the river is consistent along the study length and is approximately 1 in 380.

Figure D1 Photo and channel cross section for gauge 19001

Ballea Bridge Upper is a single arch bridge which causes a back up of water at higher flows. Out of bank flows bypass the bridge along the R613 and spill back into the channel downstream of the Bridge. The hydraulic model consists of 11 channel cross sections and 3 structures. The weir is represented by ISIS spill units which define its geometry. A modular limit and weir coefficient determine the weir calculations for this structure. Bypass flows at Ballea Bridge Upper are also represented by a spill unit with survey data from the roadway defining its geometry. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 41m3/s. The downstream boundary consists of a normal depth boundary unit. The model was calibrated against gauged data with adjustments to the following hydraulic parameters; weir coefficients, bridge coefficients and Manning’s n. Results of the rating review and a revised rating are shown in Figure D2 and Table D1. Analysis of the results shows that spilling of floodwaters along the roadway occurs when flows in the river exceed approximately 32m3/s.


Hydrology Report

D3

G19001 at Ballea Bridge

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 10 20 30 40 50

Flow (m³/s)

Sta

ge (

m)

spot gaugings w inter spot gaugings OPW RatingHalcrow recommended C = 2.5 n=0.040 (best f it) c = 2.1 n=0.04c = 2.5 n=0.030 c = 2.5 n=0.050 c = 1.8 n = 0.04c = 2.8 n = 0.04

Bankfull stage: 1.2m ASD

Figure D2 Rating curve for gauge 19001

Table D1 Rating equation values for gauge 19001

Section Minimum stage (m)

Maximum stage (m)

C a b

1 0.00 0.26 18.00 0.00 2.60

2 0.26 0.51 23.10 0.00 2.86

3 0.51 2.00 12.53 0.00 1.97

From the graph it can be seen that the model accurately represents the rating curve based on flow gauging up to a flow of approximately 8m3/s and slightly deviates from the flow gaugings up to the maximum spot gauge at 12.83m3/s. From the graph it can be seen that there is a significant departure of the revised rating curve when compared to the OPW rating curve from approximately 13m3/s.

D1.2 Gauge 19006 – Glanmire on the Glashaboy River

The gauging station at 19006 consists of an open channel section with flood plain flows which bypass the gauging station at higher water levels. The gauge is located along the left bank of


Hydrology Report

D4

the channel. The channel is approximately 11 m in width with a minimum bed elevation of 0.836 m AOD. The Qmed value for the gauge is 37.7 m3/s.

The study reach is approximately 1 km in length and is defined by a narrow floodplain which runs along the left bank of the channel. The right bank of the channel rises steeply to the R639 which is 3.7m above the bed level at the location of the gauge. There are 2 structures along the study reach; Glanmire Bridge which is approximately 550m downstream of the gauge and an old stone weir approximately 250m downstream of the gauge. The weir defines the highest point to which medium tides flow. The approach channel to the gauge is relatively straight with a more sinuous plan form upstream downstream of the gauge. The bed slope of the river is consistent along the study length and is approximately 1 in 315.


The hydraulic model consists of 20 cross sections and 2 structures. Flood plain storage and flows are modelled using ISIS reservoir units. 2 reservoir units model floodplain storage at the upstream and downstream extent of the floodplain. The reservoirs are linked with a floodplain cross section to model flows between the reservoirs. Channel cross sections are linked with spill units which model spilling of flood waters to the flood plain. The geometry for the spills was derived from the DTM data. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 73 m3/s. The downstream boundary consists of a normal depth boundary unit. The model was calibrated against gauged data with adjustments to hydraulic parameters of weir coefficients and Manning’s n. Results of the rating review and a revised rating are shown in Figure D4 and Table D2


Hydrology Report

D5

G19006 at Glanmire

0.0

0.5

1.0

1.5

2.0

2.5

0 10 20 30 40 50 60 70 80 90

Flow (m³/s)

Sta

ge

(m

)

spot gaugings w inter spot gaugingsEPA Rating Bankfulln=0.04 c=1.7 n=0.025 c=1.7n=0.032 c=1.7 (Best calibration) Halcrow recommended





Maximum stage (m)

C a b

1 0.000 0.234 2.29051 0 1.5697

2 0.234 0.350 2.29051 0 1.5697

3 0.350 1.390 2.618 0 1.82

4 1.390 1.410 2.805 0 1.2

5 1.410 2.400 2.52 0 2.12

The hydraulic influence of the weir on water levels at the gauging station was tested by adjusting the weir coefficient and was shown to be negligible. The results show that the model accurately represents the rating curve based on spot gauging up to a flow of approximately 10m3/s. There is a significant departure of the revised rating when compared to the EPA rating for flows upwards of 12m3/s. The best fit rating curve was achieved with a Mannings n of 0.032.

D1.3 Gauge 19011 – Leemount upper on the River Lee

Gauge 19011 is located approximately 40m upstream of Leemount Bridge on the left bank of the River Lee. The gauging station is located on an open channel section with good high flow measurements. The channel is uniform in width along the reach with a channel width of


Hydrology Report

D6

approximately 54m at the gauging station. The minimum bed level at the gauging site is 4m AOD. Flows along the river reach are controlled by the operation of Inishcarra reservoir 8.8 km upstream of the gauge. The Qmed value for the gauge is 208.6m3/s.

The study reach extends for approximately 500m upstream of Leemount Bridge and 250m downstream of Leemount Bridge. The bridge is the only major hydraulic structure along the study reach. The Shournagh River joins the River Lee 50m downstream of Leemount Bridge. The approach channel to the gauge is relatively straight and uniform. Downstream of the bridge the channel turns through 90 degrees. Upstream of the bridge floodplains exist on both the left and right banks with lower and more extensive flood plains along the right bank. Downstream of the bridge the floodplains are more extensive. The bed slope averages at 1 in 1500 along the full study length, with significant changes in bed slope immediately upstream and downstream of Leemount Bridge. The channel slopes upwards towards the upstream face of the bridge and downwards on the downstream face and probably as a result of both deposition and erosion respectively.


The hydraulic model consists of 18 cross sections. Floodplain flows are modelled through combined channel and floodplain cross sections. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 414m3/s. The downstream boundary consists of a normal depth boundary unit. The model was calibrated against gauged data with adjustments to hydraulic parameters of bridge coefficients and Manning’s n. Results of the rating review are presented in Figure D6 and Table D3.


Hydrology Report

D7

19011 at Leemount Bridge Upper

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 50 100 150 200 250 300 350 400

Flow (m³/s)

Sta

ge (

m)

spot gaugings w inter spot gaugingsHalcrow recommended n=0.04 C=1.0 (Best fit)ESB Rating n=0.034 C=1n=0.048 C=1 Spot gaugings at gauging stationC = 0 C = 1.4





Maximum stage (m)

C a b

1 0.000 2.000 50.576 -0.315 1.764

2 2.000 3.100 41.955 -0.088 1.664 3 3.100 3.900 31.681 0.202 1.760 4 3.900 4.200 38.076 -0.280 1.794

There is a good range of spot gauging including gauging with out of bank flows which to calibrate the model. From the graph there is evidence of the hydraulic influence of the bridge at higher flows which causes the backup of water and model instabilities. The best fit rating was achieved with a Manning’s n of 0.040.


Hydrology Report

D8

D1.4 Gauge 19012 – Leemount Lower on the River Lee

The gauging station at Leemount Lower is located on the right bank of the River Lee approximately 130m downstream of Leemount Bridge. The confluence of the River Lee and Shournagh River is approximately 60m upstream on the left bank of the River Lee. The gauging station is an open channel section with a minimum bed level of 4.32mAOD and is 51m wide. The gauge is situated above the floodplain so high flow measurements should be obtainable. Extensive floodplains are located along the left of the channel. The floodplain along the right of the channel is limited by the presence of the road embankment to the N22 Flows along the river reach are controlled by the operation of Inishcarra reservoir 8.8km upstream of the gauge. The Qmed value for the gauge is 185.3m3/s.

The study reach extends from upstream of Leemount Bridge to approximately 300m downstream of the gauge. The study reach is defined by wide floodplains downstream of the bridge. Leemount Bridge is the only major structure along the study reach and is approx 175m upstream of the gauge. The Shournagh River joins the River Lee approximately 125m upstream of the gauge. The bed slope averages at 1 in 1500 along the full study length, with significant changes in bed slope immediately upstream and downstream of Leemount Bridge. The channel slopes upwards towards the upstream face of the bridge and downwards on the downstream face and probably as a result of both deposition and erosion respectively.


During the early 1990’s significant land reclamation works were carried out at the right bank of the channel at the location of the gauge. The ESB noted that these works will have had a substantial affect on the rating curve particularly at low flows. There is limited spot gauge data available post these works.

The hydraulic model consists of 18 cross sections. Floodplain flows are modelled using merged channel and floodplain cross sections. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 414m3/s. The downstream boundary consists of a normal depth boundary unit. Results were exported to the analysis sheet with changes to hydraulic parameters of bridge coefficients and Manning’s n. Results of the rating review are presented in Figure D8 and Table D4.


Hydrology Report

D9

19012 at Leemount Bridge Lower

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 50 100 150 200 250 300 350 400

Flow (m³/s)

Sta

ge (

m)

spot gaugings w inter spot gaugings Halcrow recommendedn=0.048 ESB Rating n=0.034n=0.040 (Best f it) Spot gauge data - post 1990





Maximum stage (m)

C a b

1 0.000 2.600 58.332 -0.505 1.684

2 2.600 2.980 51.432 -0.405 1.799 3 2.980 3.180 52.052 -0.675 2.081

4 3.180 3.500 51.252 -0.609 2.090

The rating curve shows good agreement with spot gauge data for both the pre-reclamation works and post reclamation works which would suggest that the reclamation works resulted in minimal impact on flows in the river. The best fit rating is achieved with a Manning’s n of 0.040,

D1.5 Gauge 19013 - Inishcarra on the River Lee

Gauge 19013 is located approximately 1km downstream of Inishcarra dam on the left bank of the river. Flows in the channel are controlled by the operation of the Inishcarra dam. The channel is approximately 50m wide at the location of the gauge and has a minimum bed level of 11.475mAOD


Hydrology Report

D10

The study reach extends from approximately 1.5km downstream of Inishcarra Dam to 1.7km further downstream. The river is confined to a narrow valley downstream of the dam and flows through a two stage channel. Further downstream, floodplains exist on the left bank which open out to the right and left banks nearer to Ballincollig. The channel is consistent in width and is relatively straight. There are no structures along the study reach and the bed is relatively flat with a bed slope of approximately 1 in 5000. The Qmed value for gauge 19013 is 218.5m3/s.


The hydraulic model consists of nine channel cross sections with floodplain flows modelled using merged channel and floodplain cross sections. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 440m3/s. The downstream boundary consists of a normal depth boundary unit. Roughness coefficients were tested in the sensitivity analysis with results of the rating review presented in Figure D10 and Table D5..


Hydrology Report

D11

19013 at Inishcarra

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 50 100 150 200 250 300 350 400

Flow (m³/s)

Sta

ge (

m)

spot gaugings w inter spot gaugings Halcrow recommended

n=0.040 ESB Rating n=0.028

n=0.034 n=0.030 (Best f it)





Maximum stage (m)

C a b

1 1.000 4.000 39.604 0.000 1.735

All spot gaugings for gauge 19013 were recorded at a permanent section 300m downstream of Inishcarra dam. There is a wide scatted in the spot gaugings at lower flows which the ESB attribute to weed growth in the channel. The ESB have calculated the rating curve based on spot gaugings above 13.4 m AOD. As we are mainly interested in high flow conditions, the revised rating curve is also based on spot gaugings above this level.

The modelled rating curve shows good agreement to ESB rating with relatively low Manning’s values. The best fit is achieved with a Manning’s n value of 0.030. From the site visit to the gauge it was noted that the channel was relatively clean and straight along the study reach which is in keeping with a low n value.

D1.6 Gauge 19014 – Dromcarra on the River Lee

Dromcarra gauging station is located upstream of Dromcarra Bridge on the right bank of the River Lee. The gauge is located on an open channel section approximately 20m in width and with a minimum bed level of 65.694mAOD. The gauge is located well above the floodplain so


Hydrology Report

D12

good high flow measurements should be obtainable. The Qmed value for gauge 19014 is 71.8m3/s.

The study reach extends for approximately 500m upstream of the gauge and 900m downstream of the gauge. Dromcarra Bridge is the most significant structure along the study reach and is 153m downstream of the gauge. A flat crested weir is located immediately downstream of the bridge. The gauging cross section is reasonably representative of the channel along the study reach The right bank of the channel rises steeply to the R587 which prevents out of bank flows along the right bank. Out of bank flows will spill into the floodplain along the left bank of the channel and continue in a downstream direction. The spilling of flood waters past the bridge is prevented by both the embanked ground to the R587 and the high bridge abutments. The channel is relatively straight along the study reach and has a bed slope of 1 in 370.


The hydraulic model consists of ten channel cross sections with floodplain flows modelled using merged channel and floodplain cross sections. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 182m3/s. The downstream boundary consists of a normal depth boundary unit. Roughness coefficients, weir coefficients and bridge coefficients were tested in the sensitivity analysis with results of the rating review presented in Figure D12 and Table D6.


Hydrology Report

D13

19014 at Dromcarra

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Flow (m³/s)

Sta

ge (

m)



n=0.028 Bridge af f lux = 0.5 Weir coefficient c = 1.5





Maximum stage (m)

C a b

1 0.000 1.149 38.214 -0.250 1.901

2 1.149 1.780 36.160 -0.249 1.560 3 1.780 3.000 34.223 -0.255 1.690

The spot gaugings show there is a seasonality issue between winter and summer spot gaugings. This is probably caused by weed growth in the channel during summer months. The rating curve shows good agreement to ESB rating up o a flow of 40m3/s. The steeper upper rating suggested by the model shows the influence of Dromcarra Bridge on water levels at the gauge for higher flows.

D1.7 Gauge 19015 – Healy’s Bridge on the Shournagh River

Gauge 19015 is located downstream of Healy’s Bridge on the left bank of the Shournagh River. The gauge is located at an open channel section and has a width of 21.46m and a minimum bed level of 10.734mAOD. High flow measurements should be obtainable as the gauge is located well above the river bed. The Qmed value for the gauge is 70.5m3/s.


Hydrology Report

D14

The study reach extends for 1.5km with the river confined to a narrow valley for the full extent of the study reach. Healy’s Bridge and the weir immediately downstream of the bridge are the two main structures along the study reach. Spilling of floodwaters past Healy’s Bridge is constricted by the high bridge abutments and road embankment. The bed slope averages at 1 in 470 over the first 1000m with a steeper bed slope of 1 in 200 over the remainder of the reach.


The hydraulic model has been constructed using twelve channel cross sections. The two stage channel has been created by merging the channel cross sections with DTM data. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 138m3/s. The downstream boundary consists of a normal depth boundary unit. Roughness coefficients, weir coefficients and bridge coefficients were tested in the sensitivity analysis with results of the rating review presented in Table D7 and Figure D14.



Maximum stage (m)

C a b

1 0.000 1.264 20.977 -0.150 1.855

2 1.264 1.553 20.957 -0.150 1.855

3 1.553 1.710 20.200 -0.132 1.985 4 1.710 2.300 19.870 -0.159 2.150

5 2.300 2.700 19.870 -0.139 2.155


Hydrology Report

D15

19015 at Healys Bridge

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

Flow (m³/s)

Sta

ge (

m)



n=0.055 n=0.038 (Best f it)



The rating curve shows good agreement to the spot gauge data and calibrates best with a Manning’s n value of 0.038.

D1.8 Gauge 19016 – Oven’s Bridge on the River Bride

Gauging station 19016 is located approximately 5m upstream of Oven’s Bridge on the right bank of the channel. The gauge is located on an open channel section which has a minimum bed level of 20.795m AOD and a maximum width of approximately 22m. High flow measurements should be obtainable as the gauge is located above the floodplain. The Qmed

value for gauge 19016 is 29.5m3/s.

The study reach extends for 720m upstream of the gauge and a further 575m downstream of the gauge. The approach channel to the gauge is straight with the river showing a sinuous plan form further upstream and downstream of the bridge. Ovens Bridge is the main structure along the study reach and comprises of three box sections. A weir and fish pass are located directly downstream of the bridge. Floodplain flows will occur on both the left and right banks of the channel. Floodplain flows are constricted at Oven’s Bridge by the N22 road embankment which will cause floodplain flows to pond upstream of the bridge. Upstream of the bridge the channel has a bed slope of 1 in 390. Downstream of the bridge the bed slope increases to 1 in 180.


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D16


The hydraulic model has been constructed using 15 channel cross sections. The floodplains are represented by merging the channel cross sections with the DTM data. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 120m3/s. The downstream boundary consists of a normal depth boundary unit. Roughness coefficients, weir coefficients and bridge coefficients were tested in the sensitivity analysis with results of the rating review presented in Figure D16 and Table D8.

19016 at Ovens

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30 40 50 60 70 80 90 100 110 120

Flow (m³/s)

Sta

ge (

m)

spot gaugings w inter spot gaugings ESB Rating

n=0.028 (best calibration) Halcrow rating n=0.022

n=0.04

Bankfull stage:1.89 mASD



Hydrology Report

D17



Maximum stage (m)

C a b

1 0.000 0.270 11.721 -0.050 1.811

2 0.270 0.600 43.602 -0.050 2.679 3 0.600 2.000 30.000 -0.050 1.980

The ratings at gauge 19016 were affected by reconstruction works to the bridge and the weir in the 1970’s and 1980’s. The latest ESB rating applied to values recorded post 1984.

There is a limited range of spot gauging to calibrate the rating curve. The model was calibrated using spot gaugings post 1984. The rating calibrates best with a Manning’s n value of 0.028. The revised rating shows a significant difference to the ESB rating for higher flows. The steeper curve of the revised rating indicates that the road embankment to the bridge has a hydraulic influence on water levels at the gauge not reflected in the ESB rating.

D1.9 Gauge 19018 – Tower on the Shournagh River

The gauge at Tower is an open channel section located on the left bank of the Shournagh River approximately 30m upstream of Tower Bridge. The channel is approximately 9m wide and has a minimum bed level of 19.84mAOD. The gauge is located approximately 1m above the top of bank level which may affect the measurement of very high water levels. The gauge recording equipment has been removed from this site. The Qmed value for the gauge is 70.2m3/s.

The channel cross section at the gauge is reasonably representative of the study reach which extend for 450m upstream of the gauge and 380m downstream of the gauge. Upstream of the bridge out of bank flows will spill to a narrow floodplain along the right bank of the river. The floodplain averages 20m in width and is bounded by an earth embankment which protects properties in Tower. The left bank of the channel is heavily forested and has a steep gradient from the top of the bank apart from an area just upstream of the bridge which is a forested flat ground approximately 20m in width. Downstream of the bridge an embankment protects floodplain along the left bank of the channel. At the golf course the right bank floodplain opens out. Tower Bridge is a four arch bridge and the only structure along the study reach. A bypass culvert is located on the right bank of the bridge for passing higher river flows. At higher flows the bridge will constrict flows and cause the back up of water. The approach channel to the gauge is relatively straight with the river showing a sinuous plan form further upstream and downstream of the bridge. The bed slope is consistent along the study reach at 1 in 415.


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D18


The hydraulic model has been constructed using twelve channel cross sections. The floodplains are represented by merging the channel cross sections with the DTM data. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 108m3/s. The downstream boundary consists of a normal depth boundary unit. Roughness coefficients and bridge coefficients were tested in the sensitivity analysis with results of the rating review presented in Figure D18 and Table D9.

19018 at Tower

0.0

0.5

1.0

1.5

2.0

2.5

0 10 20 30 40 50 60 70 80 90 100 110

Flow (m³/s)

Sta

ge (

m)

spot gaugings w inter spot gaugings n=0.040EPA rating 2003 n=0.050 n=0.034C = 1.2 C=0.8 EPA Rating 2005Halcrow recommended




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Maximum stage (m)

C a b

1 0.084 0.300 10.2714 0 1.5905

2 0.300 0.532 36.8606 0 2.65 3 0.532 1.020 17.915 0 1.681 4 1.020 1.500 17.995 0 1.835

5 1.500 2.000 18.175 0 1.845 6 2.000 2.700 18.305 0 1.844

The rating curve shows good agreement to EPA spot gaugings with a best fit achieved with a Manning’s n value of 0.040.

D1.10 Gauge 19020 – Ballyedmond on the Owennacurra River

The gauge at Ballyedmond is an open channel section located at the interchange between a steep sided valley and open flat floodplains. The gauge is sited high enough up above the top of the bank to gain accurate high flow records. The gauging channel section is approximately 10m wide and has a minimum bed level of 23.028mAOD. The Qmed value for gauge 19020 is 22.5m3/s.

Upstream of the gauge the river meanders through a steep sided valley with the R626 flanking the right bank of the river. The Leamlara River joins the Owennacurra River approximately 50m upstream of the gauge. Directly downstream of the gauge the valley opens out with extensive floodplains along the left bank of the River. Out of bank flows along the right bank of the channel are constricted by the R626 embankment. The only structure along the study reach is a wooden footbridge approximately 350m downstream of the gauge. The footbridge will have a minimal impact on water in the river. The bed slope is relatively consistent along the 1km study reach at 1 in 180.


The hydraulic model has been constructed using ten channel cross sections. The floodplains are represented by merging the channel cross sections with the DTM data. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 50m3/s. The downstream boundary consists of a normal depth boundary unit. Roughness coefficients were


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D20

tested in the sensitivity analysis with results of the rating review presented in Figure D20 and Table D10.

G19020 at Ballyedmond

0.0

0.5

1.0

1.5

2.0

2.5

0 10 20 30 40 50

Flow (m³/s)

Sta

ge (

m)

spot gaugings w inter spot gaugings Halcrow recommendedn=0.040 n=0.050 EPA Ratingn=0.035 n=0.045 (Best f it)





Maximum stage (m)

C a b

1 0.000 0.374 28.986 0.000 3.428

2 0.374 0.895 10.011 0.000 2.347

3 0.895 1.417 9.530 0.000 1.901 4 1.417 2.000 9.564 0.000 1.931 5 2.000 2.500 9.217 0.000 1.995

The rating curve shows good agreement to EPA spot gaugings with the higher range of Manning’s n values. The best fit was achieved with a Manning’s n of 0.045.

D1.11 Gauge 19031 – Macroom on the Sullane River

Gauge 19031 is an open channel gauging section located on the right bank of the Sullane River at the Macroom Sewage Treatment works. The channel is 45m in width and has a minimum bed level of 62.263mAOD at the gauging station. The cross section is reasonably representative of the channel along the study reach. The gauge is located approximately


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D21

1.3km downstream of Macroom Bridge and is approximately 800m upstream of New Bridge. The River Laney joins the River Sullane 170m upstream of New Bridge. Out of bank flows will spill to a narrow floodplain along the left bank of the river with embankments limiting floodplain flows along the right bank of the channel. The river is sinuous in plan form and has a bed slope which averages 1 in 550 along the study reach. There are two structures along the study reach; New Bridge and a flat crested weir immediately downstream of New Bridge. The Qmed value for gauge 19031 is 141.7m3/s.


The hydraulic model has been constructed using 25 channel cross sections. The floodplains are represented by merged channel cross sections and LIDAR DTM data. Two structures along the study reach are represented with ISIS weir and bridge units. The upstream model boundary consists of an unsteady hydrograph with a peak flow of 242m3/s. The downstream boundary consists of a normal depth boundary unit. Roughness and structure coefficients were tested in the sensitivity analysis with results of the rating review presented in Figure

D20 and Table D10.



Maximum stage (m)

C a b

1 0.000 2.900 33.976 -0.030 1.811

2 2.900 3.100 34.076 -0.060 1.829


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D22

19031 in Macroom

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240

Flow (m³/s)

Sta

ge (

m)


ESB Rating n=0.032 n=0.040

n=0.042 (Best calibration) 0.048

lBankfull stage:2.353m ASD


The rating curve shows good agreement to ESB spot gaugings for the full range of spot gaugings. The rating curve calibrates best with a channel Manning’s n value of 0.042.

D2 Hydrometric gauge growth curve

D2.1 Overview

Appendix D3 and D4 provides further elaboration on the hydrological analysis described in Section 6. In particular, the rationale behind the L-Moments analysis, Storm-Flood return period relationship and unit hydrograph methodology is presented.

D2.2 Statistical distribution

The hydrological statistical analysis undertaken is based on the L-Moments distribution fitting techniques presented in the FEH and Hosking et al 1997.

Typically, annual maximum flood records in Ireland have tended to be analysed using the Extreme Value 1 distribution, fitted using the Method of Moments technique (NERC, 1975 Vol

I S1.3.4 and Cunnane et al 1975). However research undertaken since the FSR was published now suggests that the Method of Moments technique can result in poor results when data is strongly skewed. “since skewness is a feature of many flood series, L-moments

are the preferred over conventional moments in flood frequency analysis” (IOH, 1999 Vol 3

S14.2.1).


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D23

While the Method of Moments approach is based on defining the mean, scale and skewness of a data series, the L-Moments approach is differentiated by determining the mean, scale and skewness of linear combinations of a data series. The L-Moments are often reduced to the dimensionless L-Moment ratios, to assist in comparison and the pooling of data series. The three ratios are defined as the L-CV (coefficient of L-variation), L-skewness (a shape parameter) and L-kurtosis (a description of the peak or bulge of a distribution)

The determination of a data series’ L-Moment ratios is a multi step process, yet common for all distributions.

Two statistical distributions are commonly considered in the analysis of annual maximum flood records in Ireland; The Generalised Extreme Value (GEV) (of which the EV1 distribution is special case) and the Generalised Logistic (GL). The GEV distribution was found to be the most representative distribution for flood event analysis in the FSR; however the subsequent FEH found that UK catchments had a stronger tendency towards the GL distribution. The FEH also outlined further underlying reasoning behind the appropriateness of the GL distribution, including the GL resulting in fewer bounded above growth curves being derived than the GEV distribution. While other distributions do exist, there is a lack of sufficient research available at the time of the study to suggest their appropriateness for use in flood event analysis in Ireland.

Utilising the L-Moments technique to the study data sets, the most representative distribution is determined by the proximity of site L-Moment ratios to the theoretical distribution. Figure

D23 illustrates that most of the site L-Moment ratios, including the study weighted average (weighted based on gauge record length) are in a closer proximity to the theoretical GEV distribution as opposed to GL. On this basis, the GEV distribution was found to be the most appropriate distribution for the analysis of the Lee catchment. This finding appears to be consistent with ongoing research being undertaken by the Flood Studies Update researchers on catchments throughout Ireland.

Due to the potential influence of the operation of the hydroelectric dams on the distribution of extreme flows, averaged L-Moment ratios excluding the downstream Lee gauges (19013, 19012 and 19011) were used.


Hydrology Report

D24

GL

GEV

-0.1

0

0.1

0.2

0.3

0.4

0.5

-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

L-Skewness

L-K

urt

osis

Study Averaged (Total) Study Averaged (Without Gauges D/S of Reservoirs)

Figure D23 Hydrometric gauge L-Moment Ratio diagram compared with theoretical GEV and GL distributions

D2.3 Study-rainfall growth curve relationship

One inherent difficulty with a rainfall runoff approach is while the model can be calibrated to match statistical derived design floods at a defined return period (or in the case of this study the index flood Qmed); the model does not automatically guarantee that rainfall-runoff derived flood peaks match the statistically derived floods for different return periods. The FSR approached the discrepancy by defining an averaged relationship between flood return period and storm return period (FSR Figure I6.54) where recommended FSR catchment characteristics are used. However, within the seven catchments considered by the FSR, considerable variation existed. For example, the FSR found that the 50 year flood was produced from storm return periods ranging between 60 and 128 years, averaged at 81 years.

Rigid application of the FSR relationship ignores regional growth curve differences, particularly relevant in the case of FSR application in Ireland (UK rainfall growth curves used in conjunction with Ireland regional flood growth curve) or in the case of this study where study specific rainfall and flood growth curves have been developed.

The FEH continues of the FSR rainfall-flood growth curve approach, while acknowledging that considerable variation existed in the seven catchments used by the FSR (FEH V4 3.1.1). However, the recently published FEH supplementary report 1 (FEHS1) (CEH 2007) provides a more comprehensive consideration of the means of calibrating the FSR rainfall-runoff method than suggested in either the FSR or FEH. The report identifies three alternatives to


Hydrology Report

D25

calibrating the rainfall runoff method (broadened here to be relevant to the FSR method) (FEHS1 D.2):

• Vary rainfall depth with return period (as done in the FSR and FEH);

• Vary soil moisture with return period;

• Alter the rainfall-runoff equations to alter the growth curve relationship (FEH S1).

The FEH S1 approach adopts the third alternative by altering the loss model to include a calibration factor. The approach also fixes the storm return period to be equal to the flood return period. Unfortunately, the use of the FEH S1 is not possible in this study due to the absence of defined Irish catchment parameters and the potential inappropriateness of using empirical relationships derived solely from UK data.

In the case of this study, the large amount of statistical record warrants a redefining of the flood-storm return period relationship to ensure that generated hydrographs are consistent with the derived study growth curve.

Figure D24 illustrates the relationship between the growth curve derived from direct application of the rainfall runoff method (where flood return period equals storm return period) and the study hydrology growth curve. For flood events less than 1 in 100 years, the corresponding storm return period is found to under predict the flood. However, flood events greater than the 1 in 100 year are found to be considerably over predicted by the corresponding storm return period. Table D12 provides the recommended flood-storm relationships for the Lee CFRAM Study, in relation to the FSR. The recommended study storm return periods adjust the rainfall-runoff curve shown on Figure D24 to correspond with the Study growth curve.

Table D12 Study flood-storm return period relationship compared with the Flood Studies Report

Storm Return Period (yr) Flood Return

Period (yr) Recommended

Study Flood Studies

Report

2 2 - 5 8 8 10 17 17 50 56 80 100 98 140 200 173 - 1000 578 1000


Hydrology Report

D26

2 5 1005010 1000200

1.00

1.50

2.00

2.50

3.00

3.50

0 1 2 3 4 5 6 7

Gumbel Reduced Variation

Gro

wth

Facto

r (R

eb

ased

to

Qm

ed

) Rainfall Runoff Method

Study Hydrology Growth Curve

Return Period (yr)

Figure D24 Study growth curve derived from hydrometric records compared with Rainfall Runoff Method growth curve

D2.4 Gauge growth curves

Calculated growth curves at hydrometric stations are contained in Figures D25 to D35. The Growth curves have been calculated using the L-Moments fitting techniques outlined previously. The Generalised Logistic growth curve has a tendency to predict higher flood events, than the Generalised Extreme Value distribution adopted in this study at all gauges.

19001: Owenboy at Ballea

GEV

GL

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4

-4 -2 0 2 4 6 8Gumbel Reduced Variate

Gro

wth

facto

r (Q

/Qm

ed

)

Figure D25 19001- Owenboy at Ballea GEV and GL growth curves


Hydrology Report

D27

19006: Glashaboy at Glanmire

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4


Gro

wth

facto

r (Q

/Qm

ed

)

Figure D26 19006- Glashaboy at Glanmire GEV and GL growth curves

19011: Lee at Upper Leemount

GEV

GL

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4


Gro

wth

fa

cto

r (Q

/Qm

ed

)

Figure D27 19006- Glashaboy at Glanmire GEV and GL growth curves


Hydrology Report

D28

19012: Lee at Lower Leemount

GEV

GL

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4

-4 -2 0 2 4 6 8


Gro

wth

fa

cto

r (Q

/Qm

ed

)

Figure D28 19012- Lee at Lower Leemount GEV and GL growth curves

19013: Lee at Inniscarra

GEV

GL

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4


Gro

wth

facto

r (Q

/Qm

ed

)

Figure D29 19013- Lee at Inishcarra GEV and GL growth curves


Hydrology Report

D29

19014: Lee at Dromcarra

GEV

GL

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4


Gro

wth

facto

r (Q

/Qm

ed

)

Figure D30 19014 - Lee at Dromcarra GEV and GL growth curves

19015: Shournagh at Healy's Bridge

GEV

GL

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4


Gro

wth

fa

cto

r (Q

/Qm

ed

)

Figure D31 19015 - Shournagh at Healy’s Bridge GEV and GL growth curves


Hydrology Report

D30

19016: Bride at Owens

GEVGL

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4

-4 -2 0 2 4 6 8


Gro

wth

facto

r (Q

/Qm

ed

)

Figure D32 19016 – Bride at Ovens GEV and GL growth curves

19018: Shournagh at Tower

GEV

GL

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4

-4 -2 0 2 4 6 8


Gro

wth

fa

cto

r (Q

/Qm

ed

)

Figure D33 19018 – Shournagh at Tower GEV and GL growth curves


Hydrology Report

D31

19020: Owennacurra at Ballyedmond

GEV

GL

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4

-4 -2 0 2 4 6 8


Gro

wth

fa

cto

r (Q

/Qm

ed

)

Figure D34 19020 – Owennacurra at Ballyedmond GEV and GL growth curves

19031: Sullane at Macroom

GEV

GL

Return Period (yr)

2 5 10 20 50 100 200 10000

0.5

1

1.5

2

2.5

3

3.5

4

-4 -2 0 2 4 6 8


Gro

wth

fa

cto

r (Q

/Qm

ed

)

Figure D35 19031 – Sullane at Macroom GEV and GL Growth Curves

D3 FSR unit hydrograph analysis

D3.1 Overview

The FSR unit hydrograph technique is outlined in FSR Volume 1 Chapter 6, with modifications outlined in the Flood Studies Supplementary Report 16.

The following deviations were made from the standard FSR Unit Hydrograph approach:


Hydrology Report

D32

(i) Study M5-2Day, Jenkinson’s ratio and SAAR rainfall values (Section 5.3);

(ii) Study storm-flood return period relationship (Section 6.5.2);

(iii) Study unit hydrograph (Section 6.5.1);

(iv) FEH Donor Catchment approach for ungauged catchments, where SPR and Tp values are scaled from gauged catchments (Section 6.2.3).

Modifications to the FSR approach were either made based on flow and rainfall data available (items i to iv) or advances in hydrological techniques (item iv). All alternations provide a discernable improvement in flood estimation accuracy over direct application of FSR methodologies.

D3.2 Rainfall methodology

Principle rainfall input parameters to the analysis:

• M5-2Day (Figure C5);

• Jenkinson’s Ratio (Figure C6);

• SAAR (Figure C4).

Standard FSR tables are used to translate the rainfall input parameters:

• M5-D (FSR Vol 2 Table 3.10);

• MT-D (FSR Vol 2 Table 2.9);

• ARF (FSR Vol 2 Table 5.2).

D3.3 Unit hydrograph methodology

The unit hydrograph analysis was undertaken in accordance with the steps outlined in FSR Vol1 6.8.2, with revised formula introduced in the Flood Studies Supplementary Report 16 (Table D13) and methodology modifications outlined in Section D3.1.

Primary sub catchment inputs to the analysis are outlined in Table D14. Rainfall parameters were interpolated and assigned to subcatchments using the ArcView Spatial Analyst (Tin grid) GIS package. Catchment Area, MSL, S1085, Soil indices and Urban Fraction were assigned to subcatchments using the MapInfo GIS package spatial query functions. Rainfall duration figures are provided for the critical rainfall duration.

The implementation of the unit hydrograph analysis was automated using in-house Microsoft Excel VBA programmes. Tables D15 to D17 and Figure D35 presents an example of intermediate analysis stages for the Uplee 1 subcatchment.

Full design hydrographs and spreadsheets are provided in study handover digital data.


Hydrology Report

D33

Table D13 FSR and FSSR 16 Unit Hydrograph equations

0.230.542.20.33 MSLSAARURBAN)(1283S1085Tp(0) −−−

+=

5/)0(TpT ≅

2/)0()( TTpTTp +=

RAINCWIRURAL DPRDPRSPRPR ++=

553447337230110 SSSSSSPR ++++=

)125(25.0 −= CWIDPRCWI

7.0)40(45.0 −= PDPRRAIN for P>40mm or 0 for P<40mm

)3.0(70)3.00.1( URBANURBANPRPR RURALTOTAL +−=

510)5.50.3)125(33( −

×++−= SAARCWIANSF


Hydrology Report

D35

Table D14 Existing catchment unit hydrograph parameters

Rainfall

Duration (hr)

M5-2D

ay (m

m)

r (M5-1hr/M

5-2D

ay)

Sub C

atchment

Area (km2)

Urban

SAAR

(mm

)S1085 (m

/km)

MSL

(km)

Soil1Soil2

Soil3Soil4

Soil5

upper leeuplee1

10013

83.00.21

80.30.00

117712.1

18.80.0

0.80.0

0.00.2

upper leeuplee2

10015

85.70.20

96.10.00

12578.5

23.50.0

0.50.0

0.00.5

upper leeuplee3

10011

112.40.20

74.30.01

171614.2

14.60.0

0.10.0

0.20.8

upper leeuplee4

10023

93.30.20

144.00.01

14652.2

18.30.0

0.50.0

0.20.3

upper leeuplee5

10025

80.50.22

88.40.01

11650.2

16.30.0

0.90.0

0.00.0

upper leeuplee6

10025

86.10.20

138.10.00

12850.1

13.60.0

0.50.0

0.40.1

upper leeuplee7

10011

125.00.20

54.50.00

197610.2

11.20.0

0.00.0

0.40.6

upper leeuplee8

10029

101.30.20

116.20.00

15510.4

18.20.0

0.00.0

0.70.3

upper leeU

pper Lee to 19014100

21108.9

0.20170.8

0.001687

4.129.4

0.00.0

0.00.6

0.4

upper leeU

pper Lee to 19031100

1399.8

0.20218.3

0.011551

7.532.8

0.00.3

0.00.2

0.5tranm

oretran1

1007

80.20.25

7.60.71

10632.8

3.40.0

1.00.0

0.00.0

tranmore

tran2100

382.8

0.252.1

0.091106

64.81.7

0.01.0

0.00.0

0.0tranm

oretran3

1005

80.00.25

3.40.20

107120.0

4.70.0

1.00.0

0.00.0

tranmore

tran4100

380.4

0.253.5

0.201086

55.42.5

0.01.0

0.00.0

0.0tranm

oretran5

1005

81.50.25

4.60.40

10889.1

2.20.0

1.00.0

0.00.0

owennacurra

owen1

10025

82.20.25

73.90.00

110011.2

13.70.0

0.90.0

0.00.1

owennacurra

owen2

10023

79.90.25

32.30.04

10724.9

5.40.0

1.00.0

0.00.0

owennacurra

owen3

10023

82.50.25

36.90.00

11259.3

12.30.0

1.00.0

0.00.0

owennacurra

owen4

10023

78.50.25

5.60.17

10320.9

2.90.0

1.00.0

0.00.0

owennacurra

owen5

10021

78.20.25

9.90.11

10332.1

1.90.0

1.00.0

0.00.0

owennacurra

owen6

10021

77.40.25

11.30.00

10100.3

2.00.0

1.00.0

0.00.0

Ow

enboyO

wenboy to 19001

10023

83.80.25

103.60.02

11831.1

24.00.0

1.00.0

0.00.0

owenboy

boy1100

1180.6

0.259.7

0.041091

2.42.8

0.01.0

0.00.0

0.0

owenboy

boy2100

582.3

0.253.0

0.241114

39.03.3

0.01.0

0.00.0

0.0

owenboy

boy3100

383.4

0.252.1

0.401128

39.83.1

0.01.0

0.00.0

0.0

owenboy

boy4100

1384.4

0.2517.4

0.001156

1.15.9

0.01.0

0.00.0

0.0

owenboy

boy5100

585.0

0.252.3

0.001191

38.22.3

0.01.0

0.00.0

0.0

owenboy

boy6100

585.0

0.256.4

0.001200

41.72.1

0.01.0

0.00.0

0.0ow

enboyboy7

10011

85.00.24

35.00.00

120813.7

8.80.0

1.00.0

0.00.0

owenboy

boy8100

1385.0

0.2523.4

0.001207

1.06.6

0.01.0

0.00.0

0.0ow

enboyboy9

10011

81.30.25

25.70.12

10951.5

4.40.0

1.00.0

0.00.0

owenboy

boy10100

1385.0

0.244.2

0.001215

1.82.9

0.01.0

0.00.0

0.0

lower lee

lowlee1

10013

81.30.24

63.40.00

11336.8

13.80.0

1.00.0

0.00.0

lower lee

lowlee2

10013

82.20.22

70.30.00

11388.8

20.40.0

0.70.0

0.20.2

lower lee

lowlee3

10011

80.40.24

24.50.01

10869.5

7.70.0

1.00.0

0.00.0

lower lee

lowlee4

10013

80.50.22

41.20.00

108611.0

7.50.0

1.00.0

0.00.0

lower lee

lowlee5

10011

80.20.24

8.60.20

10401.0

6.70.0

1.00.0

0.00.0

lower lee

lowlee6

1005

80.40.25

7.70.74

10524.4

6.30.0

1.00.0

0.00.0

lower lee

lowlee7

10011

81.50.24

9.50.09

10812.9

2.30.0

1.00.0

0.00.0

lower lee

lowlee8

1007

83.40.24

6.60.00

113428.3

4.70.0

1.00.0

0.00.0

lower lee

lowlee9

1005

83.60.25

10.60.07

112924.6

4.10.0

1.00.0

0.00.0

lower lee

lowlee10

1007

84.10.24

11.90.00

115221.1

7.30.0

1.00.0

0.00.0

lower lee

lowlee11

10023

83.90.23

62.90.00

11641.5

16.10.0

1.00.0

0.00.0

lower lee

lowlee12

10015

87.80.21

49.20.00

12498.2

16.30.0

0.40.0

0.60.0

lower lee

lowlee13

10013

80.00.25

18.60.66

10030.1

9.80.0

1.00.0

0.00.0

lower lee

lowlee14

10013

80.20.23

19.20.11

10422.3

8.80.0

1.00.0

0.00.0

lower lee

lowlee15

10013

80.00.24

15.30.11

10503.1

8.60.0

1.00.0

0.00.0

lower lee

lowlee to 19016

10023

85.60.2

112.10.00

12014.4

32.40.0

0.70.0

0.30.0

lower lee

Lowlee to 19015

10021

81.30.2

214.60.01

11147.1

29.00.0

0.90.0

0.10.1

glashaboyglash1

10023

84.20.25

38.20.00

117610.1

11.80.0

0.90.0

0.00.1

glashaboyglash2

10021

82.60.24

37.90.04

11189.4

9.20.0

1.00.0

0.00.0

glashaboyglash3

10023

84.20.25

43.70.01

11179.8

12.90.0

1.00.0

0.00.0

glashaboyglash4

10013

81.40.25

19.40.04

106417.3

8.00.0

1.00.0

0.00.0

glashaboyglash5

10025

80.00.25

5.90.26

10280.4

3.60.0

1.00.0

0.00.0

glashaboyG

lashaboy to 19006100

2583.4

0.2139.2

0.021126

9.821.1

0.01.0

0.00.0

0.0

carrigothillcarig1

10017

80.10.25

8.40.04

10493.0

1.10.0

1.00.0

0.00.0

carrigothillcarig2

10029

80.90.25

7.00.05

10580.9

4.60.0

1.00.0

0.00.0

carrigothillcarig3

10017

79.70.25

5.40.04

10280.1

1.00.0

1.00.0

0.00.0

carrigothillcarig4

10013

79.80.25

1.30.12

10203.3

1.20.0

1.00.0

0.00.0

bridebride1

1009

80.40.25

20.20.02

108416.4

2.90.0

1.00.0

0.00.0

bridebride2

10013

80.00.25

12.50.25

10400.3

2.70.0

1.00.0

0.00.0

bridebride3

1005

80.00.25

9.00.41

103913.9

3.80.0

1.00.0

0.00.0

Model

Rainfall Param

eters

Sub Catchm

ent R

eference

Flow

Return

Period (yr)

FSR C

atchment Param

eters


Hydrology Report

D37

Table D15 Uplee1 subcatchment unit hydrograph definition

Lee CFRAM STUDY

Subcatchment: uplee1

UNIT HYDROGRAPH CALCULATION

1. Unit Hydrograph

(a) Time to Peak, T'pTime to peak for Instantaneous Unit Hydrograph (IHU) is given by formula(refer FSSR No. 16)

Tp(0) = 283*(SI085^-0.33)*((1+URBAN)^-2.2)*(SAAR^-0.54)*(MSL^0.23)

Tp(0) = 5.37

Tp(0)Doner Catchment 4.67Now, SI085 12.0588 m/km

URBAN 0.00E+00 Urban fractionSAAR 1177.17 mm Fig II 3.1 (I) Avg Annual rainfallMSL 18.7967 km Mean stream lengthAREA 80.3 km²

Select time interval, Tau, as follows:-

Tau = 1.07 hr say 1.00 hr (rounded)

T'p = T'p + (Tau)/2 = 5.17 hr say 5.20 hr (FSSR 16)

(b) (Time) Base Length of Unit Hydrograph

T'B = 17.7 hrs

(c) Flow at Time to Peak, Q'p

Q'p = 190.9/T'p per 100 km2= 29.47 cumecs

10mm 1 hr Unit Hydrograph

Time Flow

(Hrs) (Cumecs)

0 0.04.16 13.95.20 29.58.32 10.8

17.68 0.0

10mm Unit Hydrograph

0.0

10.0

20.0

30.0

40.0

0 5 10 15 20

Hours

Q (

cu

mecs

)


Hydrology Report

D39

Table D16 Uplee1 subcatchment design rainfall analysis

Lee CFR

AMS

Subcatchment:

uplee1

2. Design Storm

D =

(1+SAAR/1000) * T'P

(FSR

)H

owever the design storm

used can be defined by the userD

FSR=

11.32hrs

Duser

13.00hrs

13intervals (needs to be an uneven num

ber)m

ultiple of1.00

hr

(b) Design Storm

Return Period

Selecting a 100 year Return Period for a flood constitutes taking a different R

eturn Period for the Design Storm

T=

98years

(c) Design Storm

Rainfall

Require

13R98

(i)2-D

ay R5 =

83m

mfrom

Fig II 3.2 (I)

(ii)r

=60-m

in, R5

=0.21

from Fig II 3.5(I)

2-Day R

5

(iii) rD

=0.62

Calculated rD

for r=0.21 D=13

(Table 3.10)(iv)

13R5 =

2-Day R

5 x rD=

51.23m

m

(v)G

rowth factor R

98/R5 for 13R

5 = 51.2 mm

is1.71

(Table 2.9)

(vi)13R

98=m

m

(vii)Areal R

eduction Factor, ARF

Total A=80.3

km²

D=

13.00hrs

ARF

=0.92

Calculate AR

F for A = 80.3022km D

= 13(Table 5.2)

(viii)D

esign Storm Areal R

ainfall, P

P=

mm

(d) percentage Run-O

ff

PRTO

TAL =PR

RU

RA

L *(1-(0.3*UR

BAN))+70(0.3*U

RBAN

)

(i)SPR

=42.95

%= (10S1 + 30S2 + 37S3 + 47S4 + 53S5) x SPR

Doner C

atchment A

djustment

where

Sone0

Stwo

0.81Fig I 4.18(I)

Sthree0

Fraction of catchment D

efined by S1…S5

Sfour####

Sfive####

(ii)D

PRC

WI =

0= 0.25 (C

WI - 125)

where

CW

I=

125for SAAR

=1177

mm

Refer to FSR

I, Fig 6.62

(iii)D

PRR

AIN

=6.03

Note if P<40m

m then D

PRR

AIN =0

Where P =

mm

(iv)PR

RU

RAL =

48.97%

=SP

R+D

PRC

WI +D

PRR

AIN

(v)PR

TOTA

L =48.97

% =

PRR

UR

AL *(1-(0.3*UR

BAN))+(70*(0.3*U

RBAN

))

(vi)N

et rainfall over catchment

=39.53

mm

=3.95

cm

(e) Storm Profile

A symm

etrical design rainfall pattern is established using the 75% W

inter Profile(Fig 3, C

unnane & Lynn's Paper)

39.53m

m is distributed over

13.00hrs in

13intervals of

1hrs each

7peak interval

12

34

56

78

910

1112

1314

1516

1718

1920

2122

23Interval of 1 hr

12

34

56

78

910

1112

130

00

00

00

00

0%

of storm duration

7.715.4

23.130.8

38.546.2

53.861.5

69.276.9

84.692.3

100.0100.0

100.0100.0

100.0100.0

100.0100.0

100.0100.0

100.0%

of storm rain

1.54.3

9.115.1

25.540.3

59.774.5

84.990.9

95.798.5

100.0100.0

100.0100.0

100.0100.0

100.0100.0

100.0100.0

100.0%

of storm interval

1.52.8

4.86.0

10.414.8

19.514.8

10.46.0

4.82.8

1.50.0

0.00.0

0.00.0

0.00.0

0.00.0

0.0

0.060.11

0.190.24

0.410.58

0.770.58

0.410.24

0.190.11

0.060.00

0.000.00

0.000.00

0.000.00

0.000.00

0.00

87.46

Net rain in interval

(cm)

80.71

80.71


Hydrology Report

D40

Table D17 Uplee1 subcatchment unit hydrograph ordinates

h1 h2 h3 h4 h5 h6 h7 h8 h9 h10 h11 h12 h13 h14 h15 h16 h17 h18 h19 h20 h21 h22 h23 h24 h25 h26 h27 h28 h29 h30 h31

3.34 6.68 10.02 13.36 26.48 24.69 18.71 12.72 10.02 8.87 7.71 6.56 5.40 4.25 3.10 1.94 0.79 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

r1 0.05 0.17 0.33 0.50 0.67 1.32 1.23 0.94 0.64 0.50 0.44 0.39 0.33 0.27 0.21 0.15 0.10 0.04r2 0.10 0.33 0.67 1.00 1.34 2.65 2.47 1.87 1.27 1.00 0.89 0.77 0.66 0.54 0.43 0.31 0.19 0.08r3 0.17 0.57 1.14 1.70 2.27 4.50 4.20 3.18 2.16 1.70 1.51 1.31 1.12 0.92 0.72 0.53 0.33 0.13r4 0.22 0.74 1.47 2.21 2.94 5.83 5.43 4.12 2.80 2.21 1.95 1.70 1.44 1.19 0.94 0.68 0.43 0.17r5 0.38 1.27 2.54 3.81 5.08 10.06 9.38 7.11 4.84 3.81 3.37 2.93 2.49 2.05 1.62 1.18 0.74 0.30r6 0.53 1.77 3.54 5.31 7.08 14.03 13.08 9.91 6.74 5.31 4.70 4.09 3.48 2.86 2.25 1.64 1.03 0.42r7 0.70 2.34 4.68 7.02 9.35 18.54 17.28 13.09 8.91 7.02 6.21 5.40 4.59 3.78 2.98 2.17 1.36 0.55r8 0.53 1.77 3.54 5.31 7.08 14.03 13.08 9.91 6.74 5.31 4.70 4.09 3.48 2.86 2.25 1.64 1.03 0.42r9 0.38 1.27 2.54 3.81 5.08 10.06 9.38 7.11 4.84 3.81 3.37 2.93 2.49 2.05 1.62 1.18 0.74 0.30r10 0.22 0.74 1.47 2.21 2.94 5.83 5.43 4.12 2.80 2.21 1.95 1.70 1.44 1.19 0.94 0.68 0.43 0.17r11 0.17 0.57 1.14 1.70 2.27 4.50 4.20 3.18 2.16 1.70 1.51 1.31 1.12 0.92 0.72 0.53 0.33 0.13r12 0.10 0.33 0.67 1.00 1.34 2.65 2.47 1.87 1.27 1.00 0.89 0.77 0.66 0.54 0.43 0.31 0.19 0.08r13 0.05 0.17 0.33 0.50 0.67 1.32 1.23 0.94 0.64 0.50 0.44 0.39 0.33 0.27 0.21 0.15 0.10 0.04r14 0.00

r15 0.00

r16 0.00

r17 0.00

r18 0.00

r19 0.00

r20 0.00

r21 0.00

r22 0.00

r23 0.00

r24 0.00

r25 0.00

r26 0.00

r27 0.00

r28 0.00

r29 0.00

0.17 0.67 1.74 3.54 7.10 12.67 20.53 29.37 39.36 49.08 57.43 59.63 56.46 49.89 43.21 36.89 30.91 25.09 20.04 15.73 11.94 8.55 5.65 3.43 1.95 1.02 0.48 0.18 0.04 0.00 0.00

3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87 3.87

4.04 4.54 5.61 7.42 10.98 16.54 24.41 33.24 43.23 52.96 61.31 63.51 60.34 53.76 47.09 40.76 34.78 28.97 23.92 19.60 15.82 12.42 9.52 7.30 5.82 4.90 4.36 4.05 3.91 3.87 3.87

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00 19.00 20.00 21.00 22.00 23.00 24.00 25.00 26.00 27.00 28.00 29.00 30.00

Total

(cumecs)

Time

(hours)

Unit Hydrograph ordinates (cumecs)Net Rain

(cm)

Sub-total

(cumecs)

Baseflow

(cumecs)

CONVOLUTION OF RAINFALL AND UNIT HYDROGRAPH ORDINATES


Hydrology Report

D41

Figure D35 Uplee1 subcatchment 100 year design hydrograph

Storm Runoff Hydrograph

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

0.00 10.00 20.00 30.00 40.00 50.00 60.00

t (hours)

Q (

cu

mecs)

D3.4 Design flows

Critical duration design flows are provided in Table D18. All design flows, including design flows for the full range of feasible durations are provided in digital format in study handover DVDs.


Hydrology Report

D41

Table D18 Critical duration design flows

Duration (hr)

2 5 10 25 50 100 200 1000Duration

(hr)2 5 10 25 50 100 200 1000

Duration (hr)

10 100 1000

upper lee uplee1 13 30.88 41.29 49.87 55.29 62.10 69.16 72.39 90.11 13 37.05 49.55 59.85 66.34 74.52 83.00 86.86 108.14 13 64.84 89.91 117.15upper lee uplee2 15 46.42 61.25 73.24 81.26 90.86 101.61 105.99 130.92 13 59.71 80.55 96.29 106.26 119.89 133.13 139.61 172.38 11 127.16 178.02 230.55upper lee uplee3 11 73.40 97.15 114.85 126.81 141.64 157.17 164.36 200.35 11 94.89 125.75 148.63 164.20 183.48 203.58 212.95 259.60 7 193.27 268.55 346.30upper lee uplee4 23 72.47 93.86 109.70 121.09 134.35 148.97 155.73 187.80 15 90.22 119.22 140.49 155.34 173.89 193.84 203.00 247.71 13 186.55 257.41 330.35upper lee uplee5 25 16.85 21.25 24.96 27.45 30.30 33.61 35.09 42.58 31 22.59 28.55 33.45 36.51 40.32 45.02 46.63 56.40 27 43.25 58.92 74.51upper lee uplee6 25 32.07 41.20 47.18 51.97 57.42 63.29 66.14 79.76 31 43.17 54.59 63.97 69.60 77.31 85.42 88.82 106.89 27 82.93 112.57 141.40upper lee uplee7 11 33.56 44.50 52.71 58.18 65.56 73.07 76.64 93.93 11 40.27 53.40 63.25 69.81 78.67 87.69 91.96 112.72 11 68.52 94.99 122.11upper lee uplee8 29 33.11 42.70 49.69 54.09 60.55 66.90 69.05 83.39 25 43.68 56.02 65.82 72.22 80.13 88.44 92.32 111.46 25 84.55 114.43 144.04tranmore tran1 7 4.16 5.63 6.88 7.64 8.58 9.71 10.21 12.82 3 6.47 8.82 10.54 11.83 13.47 15.34 16.31 20.70 5 10.84 15.34 20.34tranmore tran2 3 1.20 1.61 1.94 2.21 2.56 2.92 3.12 4.05 3 1.46 1.95 2.33 2.67 3.10 3.54 3.76 4.88 3 2.56 3.85 5.29tranmore tran3 5 1.45 1.93 2.37 2.68 3.08 3.48 3.69 4.71 7 1.91 2.53 3.13 3.54 3.99 4.48 4.71 6.03 3 4.40 6.56 9.03tranmore tran4 3 2.02 2.70 3.22 3.66 4.24 4.83 5.17 6.65 3 2.38 3.22 3.87 4.38 5.11 5.83 6.20 8.01 5 4.22 6.09 8.22tranmore tran5 5 2.60 3.41 4.23 4.78 5.45 6.12 6.49 8.27 3 3.53 4.76 5.73 6.46 7.44 8.52 9.01 11.59 3 6.29 9.26 12.48

owennacurra owen1 25 22.48 28.98 33.68 37.25 41.54 46.13 48.24 58.33 25 26.97 34.78 40.42 44.70 49.85 55.36 57.89 70.00 25 43.79 59.97 75.83owennacurra owen2 23 9.07 11.85 13.91 15.32 17.04 18.92 19.75 24.25 23 11.01 14.39 16.90 18.63 20.71 23.04 24.02 29.49 23 18.67 25.60 32.61owennacurra owen3 23 10.40 13.57 16.01 17.52 19.55 21.84 22.71 27.82 23 12.47 16.29 19.21 21.02 23.46 26.21 27.25 33.38 23 20.81 28.40 36.16owennacurra owen4 23 1.47 1.92 2.26 2.47 2.76 3.07 3.20 3.91 23 1.85 2.46 2.87 3.13 3.51 3.89 4.07 4.97 15 3.43 4.73 6.09owennacurra owen5 21 2.85 3.73 4.43 4.89 5.44 6.07 6.34 7.82 19 3.54 4.68 5.51 6.14 6.82 7.65 7.99 9.82 13 6.48 8.99 11.71owennacurra owen6 21 2.03 2.61 3.04 3.32 3.70 4.12 4.26 5.19 21 2.43 3.13 3.65 3.98 4.45 4.94 5.12 6.23 21 3.95 5.35 6.75

owenboy boy1 11 1.95 2.71 3.36 3.74 4.33 4.92 5.20 6.64 11 2.35 3.30 4.07 4.61 5.23 5.99 6.28 8.09 9 4.49 6.60 8.95owenboy boy2 5 1.01 1.33 1.67 1.92 2.19 2.53 2.66 3.47 5 1.19 1.58 1.95 2.26 2.59 2.94 3.11 4.04 3 3.37 5.14 7.15owenboy boy3 3 0.83 1.08 1.30 1.51 1.75 1.99 2.13 2.77 3 1.44 1.93 2.30 2.64 3.09 3.55 3.76 4.93 3 3.91 5.91 8.14owenboy boy4 13 3.12 4.33 5.17 5.80 6.61 7.45 7.90 9.95 13 3.74 5.20 6.21 6.96 7.93 8.94 9.48 11.94 13 6.72 9.68 12.94owenboy boy5 5 0.73 0.94 1.22 1.38 1.63 1.88 1.99 2.61 5 0.88 1.13 1.46 1.66 1.96 2.26 2.39 3.14 5 1.59 2.44 3.40owenboy boy6 5 1.89 2.51 3.25 3.76 4.33 4.95 5.29 7.04 5 2.27 3.01 3.90 4.52 5.20 5.93 6.35 8.45 5 4.23 6.43 9.15owenboy boy7 11 7.97 11.27 13.85 15.71 17.88 20.40 21.53 27.87 11 9.56 13.52 16.62 18.85 21.45 24.48 25.84 33.45 11 18.01 26.52 36.23owenboy boy8 13 4.15 5.76 6.87 7.59 8.78 9.89 10.29 13.21 13 4.98 6.91 8.24 9.11 10.54 11.87 12.35 15.86 13 8.93 12.86 17.18owenboy boy9 11 5.52 7.51 9.05 10.13 11.65 13.31 14.05 17.68 11 6.81 9.43 11.44 12.66 14.56 16.50 17.19 22.05 11 13.56 19.67 26.17owenboy boy10 13 0.86 1.21 1.49 1.67 1.91 2.18 2.27 2.92 13 1.03 1.45 1.79 2.00 2.29 2.62 2.72 3.51 13 1.94 2.84 3.80lower lee lowlee1 13 18.63 25.30 30.11 33.49 37.59 42.01 44.20 55.33 11 22.21 29.88 35.79 40.13 45.08 50.64 53.11 66.58 11 38.77 54.86 72.13lower lee lowlee2 13 23.79 32.44 38.58 42.63 48.02 53.84 56.73 70.40 13 28.54 38.93 46.29 51.15 57.62 64.61 68.08 84.48 13 50.15 70.00 91.52lower lee lowlee3 11 8.00 10.92 13.12 14.49 16.48 18.54 19.48 24.41 11 9.61 13.10 15.75 17.39 19.78 22.24 23.37 29.29 11 17.06 24.10 31.73lower lee lowlee4 13 13.10 18.13 21.54 24.16 26.98 30.58 31.96 39.80 13 15.72 21.75 25.85 28.99 32.37 36.69 38.35 47.76 13 28.00 39.75 51.74lower lee lowlee5 11 2.58 3.48 4.18 4.59 5.16 5.86 6.15 7.63 13 3.36 4.54 5.42 6.04 6.76 7.54 7.91 9.84 13 6.49 9.21 11.95lower lee lowlee6 5 4.96 6.60 8.03 9.04 10.29 11.55 12.23 15.51 3 6.83 9.28 11.17 12.40 14.28 16.16 17.14 21.88 5 11.45 16.20 21.40lower lee lowlee7 11 3.34 4.54 5.46 6.12 6.88 7.76 8.14 10.20 11 4.05 5.51 6.66 7.42 8.42 9.42 9.92 12.42 11 7.86 11.13 14.56lower lee lowlee8 7 2.82 3.78 4.62 5.21 5.90 6.66 7.03 8.94 7 3.38 4.53 5.54 6.25 7.08 7.99 8.44 10.72 7 6.00 8.66 11.62lower lee lowlee9 5 4.91 6.47 7.97 9.07 10.36 11.73 12.37 15.82 5 5.86 7.72 9.59 10.89 12.36 13.98 14.75 18.86 5 10.36 14.94 20.16lower lee lowlee10 7 4.55 6.14 7.50 8.35 9.44 10.70 11.30 14.32 7 5.45 7.37 8.99 10.02 11.33 12.84 13.56 17.18 7 9.74 13.91 18.61lower lee lowlee11 23 13.40 17.85 21.06 23.17 25.72 28.98 30.33 36.96 23 16.08 21.42 25.28 27.80 30.86 34.77 36.39 44.35 23 27.38 37.67 48.05lower lee lowlee12 15 17.11 23.15 27.45 30.48 34.14 38.40 40.30 49.72 15 20.54 27.78 32.94 36.58 40.97 46.08 48.36 59.67 15 35.68 49.92 64.64lower lee lowlee13 13 6.08 8.12 9.57 10.59 11.89 13.30 13.95 17.21 11 8.47 11.28 13.53 14.99 16.74 18.68 19.57 24.25 7 19.47 26.92 35.25lower lee lowlee14 13 5.56 7.60 9.03 9.97 11.25 12.66 13.26 16.48 13 7.06 9.50 11.30 12.63 14.21 15.86 16.75 20.84 11 13.16 18.43 24.22lower lee lowlee15 13 5.20 7.03 8.43 9.35 10.58 11.82 12.46 15.46 11 6.47 8.72 10.56 11.74 13.15 14.83 15.45 19.26 11 12.24 17.13 22.50glashaboy glash1 23 11.60 15.11 17.90 19.70 21.80 24.40 25.44 31.03 23 13.92 18.13 21.48 23.64 26.16 29.27 30.53 37.24 23 23.27 31.71 40.35glashaboy glash2 21 11.04 14.34 16.93 18.51 20.86 23.18 24.21 29.63 23 13.64 17.76 21.04 23.10 25.83 28.66 29.90 36.66 23 23.06 31.54 40.27glashaboy glash3 23 12.39 16.18 19.25 21.02 23.32 26.05 27.29 33.30 23 14.86 19.42 23.10 25.22 27.98 31.26 32.75 39.96 25 25.12 34.29 43.57glashaboy glash4 13 5.98 8.01 9.50 10.59 11.91 13.35 14.01 17.32 13 7.22 9.67 11.47 12.80 14.39 16.14 16.93 20.93 13 12.90 18.17 23.51glashaboy glash5 25 1.42 1.83 2.15 2.35 2.61 2.89 3.03 3.68 25 1.89 2.38 2.79 3.07 3.42 3.79 3.98 4.81 21 3.42 4.73 5.99carrigothill carig1 17 2.51 3.31 3.89 4.32 4.83 5.40 5.63 6.97 13 2.97 3.97 4.72 5.23 5.87 6.54 6.87 8.51 13 5.32 7.43 9.64carrigothill carig2 29 1.58 2.02 2.34 2.56 2.83 3.15 3.29 3.99 29 1.94 2.47 2.88 3.14 3.46 3.87 4.02 4.88 29 3.23 4.35 5.50carrigothill carig3 17 0.88 1.12 1.29 1.42 1.56 1.74 1.80 2.20 19 1.11 1.41 1.63 1.80 1.98 2.21 2.29 2.78 19 1.84 2.49 3.15carrigothill carig4 13 0.43 0.57 0.68 0.75 0.84 0.95 0.99 1.23 13 0.55 0.73 0.87 0.96 1.09 1.22 1.27 1.57 11 1.00 1.40 1.82

bride bride1 9 9.05 12.23 14.90 16.67 18.88 21.32 22.33 28.21 9 10.86 14.67 17.88 20.01 22.66 25.58 26.80 33.86 7 19.34 27.76 37.05bride bride2 13 3.96 5.31 6.27 6.97 7.83 8.81 9.18 11.35 13 5.16 6.95 8.25 9.22 10.28 11.51 12.10 14.87 11 10.35 14.53 18.92bride bride3 5 5.85 7.82 9.56 10.74 12.20 13.82 14.55 18.51 3 7.93 10.63 12.84 14.47 16.58 18.90 20.05 25.54 5 13.46 19.34 25.78

Sub CatchmentHydraulic

Model

High End Scenario

Return Period Design Flow Rate (m3/s)

Existing Conditions Mid Range Scenario


Hydrology Report

E1

Appendix E. Integration of hydrology and hydraulic modelling


Hydrology Report

E2

E1 Sub catchment locations

Su

b-c

atc

hm

en

t N

o.

Po

sit

ion

ing

of

Su

b-c

atc

hm

en

t C

atc

hm

en

t

3 S

ub-c

atch

men

t to

be e

xten

ded

dow

nstr

eam

to d

owns

trea

m e

xten

t of B

ally

mak

eery

. U

pper

Lee

4

Rel

ocat

e ca

tchm

ent s

light

ly d

owns

trea

m o

f Mac

room

– a

t new

rev

ised

gau

ge lo

catio

n of

190

31 (

Was

te W

ater

T

reat

men

t Wor

ks).

U

pper

lee

7

Rel

ocat

e ca

tchm

ent s

light

ly u

pstr

eam

to d

owns

trea

m e

xten

t of t

he u

rban

wat

erco

urse

for

Bal

linge

ary.

U

pper

Lee

8

Leav

e do

wns

trea

m s

ub c

atch

men

t ext

ent a

t loc

atio

n sh

own

as c

oinc

ides

with

Gau

ge 1

9014

. S

hort

sec

tion

of u

rban

ch

anne

l mid

way

dow

n su

b-ca

tchm

ent i

s be

low

a c

ontr

ol (

loug

h).

Upp

er L

ee

6 D

owns

trea

m e

xten

t sui

tabl

e at

mou

th o

f res

ervo

ir at

Car

rigad

rohi

d.

Upp

er L

ee

5 Le

ave

exte

nt d

owns

trea

m a

t 190

13 -

Urb

an c

hann

el ju

st b

elow

her

e.

Upp

er L

ee

44

Ups

trea

m e

xten

t at g

auge

190

16 a

nd d

owns

trea

m a

t lee

mou

nt b

ridge

(2

gaug

es).

Lo

wer

Lee

41

U

pstr

eam

ext

ent s

ituat

ed d

owns

trea

m o

f Cro

okst

own.

Dow

nstr

eam

ext

ent a

t gau

ge 1

9016

. Lo

wer

Lee

42

M

ove

dow

nstr

eam

ext

ent d

owns

trea

m o

f Cro

okst

own.

Lo

wer

Lee

2

Dow

nstr

eam

ext

ent l

ocat

ed a

t top

of r

ural

cha

nnel

at g

auge

190

27.

Upp

er L

ee

1 D

owns

trea

m e

xten

t of c

atch

men

t at g

auge

190

28 a

nd a

djac

ent/d

owns

trea

m o

f Dee

shar

t vill

age.

U

pper

Lee

34

M

ove

catc

hmen

t dow

nstr

eam

ext

ent f

urth

er d

owns

trea

m b

elow

urb

an c

hann

el d

esig

natio

n at

Dro

min

. Lo

wer

Lee

32

C

atch

men

t def

ined

for

all t

ribut

ary

and

dow

nstr

eam

ext

ent c

oinc

ides

with

urb

an a

rea

so o

k.

Low

er L

ee

33

Ret

ain

catc

hmen

t ext

ent a

s it

is.

Fur

ther

dow

nstr

eam

whe

re d

efin

ed a

s ur

ban

chan

nel i

s m

ainl

y ru

ral t

hrou

gh fi

elds

an

d flo

od e

mba

nkm

ents

are

in p

lace

ups

trea

m o

f tow

er b

ridge

on

true

rig

ht b

ank.

Lo

wer

Lee

45

Ret

ain

catc

hmen

t ext

ent a

s do

wns

trea

m e

xten

t is

defin

ed a

s ou

tlet i

nto

Riv

er L

ee a

t Lee

mou

nt b

ridge

. Lo

wer

Lee

31

R

etai

n do

wns

trea

m c

atch

men

t ext

ent a

s si

tuat

ed b

elow

Bla

rne

y vi

llage

urb

an a

rea.

Lo

wer

Lee

56

C

atch

men

t def

ined

dow

nstr

eam

to in

flow

to R

iver

Lee

. B

ride

57

Dow

nstr

eam

ext

ent c

oinc

ides

whe

re tr

ibut

ary

join

s w

ith R

iver

Brid

e at

dow

nstr

eam

ext

ent o

f urb

an c

hann

el

desi

gnat

ion.

B

ride

55

Cat

chm

ent d

efin

ed to

dow

nstr

eam

ext

ent o

f Brid

e tr

ibut

ary.

B

ride

46

Def

ined

dow

nstr

eam

to D

unbu

lloge

Brid

e –

all r

ural

cat

chm

ent.

Gla

shab

oy

47

Cur

rent

ly d

efin

ed to

ups

trea

m e

xten

t of t

he u

rban

cha

nnel

sec

tion,

but

brin

g do

wns

trea

m e

xten

t dow

n to

con

fluen

ce

at G

lynt

own

near

gau

ge 1

9007

. G

lash

aboy

50

All

urba

n ca

tchm

ent.

Gla

shab

oy

48

Sub

-cat

chm

ent d

owns

trea

m e

xten

t cur

rent

ly d

efin

ed a

t Cop

pera

lley

brid

ge d

owns

trea

m w

hich

is ju

st u

pstr

eam

of

conf

luen

ce.

Gla

shab

oy

49

Dow

nstr

eam

ext

ent s

et a

t Gle

nmor

e R

iver

cat

chm

ent.

Gla

shab

oy

14

Ups

trea

m s

ub-c

atch

men

t def

ined

to w

here

Lea

mla

ra R

iver

mee

ts O

wen

nacu

rra

Riv

er –

rur

al c

atch

men

t. O

wen

nacu

rra


Hydrology Report

E3

15

Join

cat

chm

ent 1

5 to

17

so th

e do

wns

trea

m e

xten

t of s

ubca

tchm

ent i

s do

wns

trea

m o

f Mid

leto

n to

wn

cent

re.

Ow

enna

curr

a 17

Jo

in w

ith c

atch

men

t 15.

O

wen

nacu

rra

16

Cov

ers

upst

ream

cat

chm

ent o

f Dun

gour

ney

Riv

er –

rur

al.

Ow

enna

curr

a 18

S

ubca

tchm

ent d

efin

es r

iver

cha

nnel

thro

ugh

Mid

leto

n.

Ow

enna

curr

a 19

T

ribut

ary

catc

hmen

t to

Dun

gour

ney

Riv

er, d

efin

ed to

the

conf

luen

ce.

Ow

enna

curr

a 20

D

owns

trea

m u

rban

ext

ent o

f Ow

enna

curr

a C

atch

men

t to

estu

ary.

O

wen

nacu

rra

30

Rur

al s

ub-c

atch

men

t enc

ompa

ssin

g a

trib

utar

y to

Ow

enbo

y.

Ow

enbo

y 27

R

ural

sub

-cat

chm

ent a

t top

of O

wen

boy

catc

hmen

t. O

wen

boy

28

Mov

e ca

tchm

ent d

owns

trea

m b

elow

urb

an c

hann

el e

xten

t. O

wen

boy

26

Leav

e su

b-ca

tchm

ent a

s is

. U

rban

ext

ent l

ocat

ed a

t bot

tom

of s

ub-c

atch

men

t. O

wen

boy

25

Sm

all c

atch

men

t with

som

e ur

ban

chan

nel a

t dow

nstr

eam

end

whe

re jo

ins

mai

n ch

anne

l.

Ow

enbo

y 24

M

ove

sub-

catc

hmen

t dow

nstr

eam

ext

ent b

elow

urb

an c

hann

el d

/s o

f Bal

lyga

rvan

. O

wen

boy

23

Sm

all c

atch

men

t with

som

e ur

ban

chan

nel a

t dow

nstr

eam

end

whe

re jo

ins

mai

n ch

anne

l.

Ow

enbo

y 22

S

mal

l cat

chm

ent w

ith s

ome

urba

n ch

anne

l at d

owns

trea

m e

nd w

here

join

s m

ain

chan

nel.

O

wen

boy

29

Fur

ther

mos

t dow

nstr

eam

sec

tion

of c

atch

men

t bel

ow g

auge

. O

wen

boy

21

Rur

al s

ub-c

atch

men

t bet

wee

n up

stre

am u

rban

cha

nnel

and

gau

ge s

ite.

Ow

enbo

y 10

S

mal

l rur

al u

pstr

eam

of u

rban

. T

ranm

ire

13

Urb

an c

hann

el.

Tra

nmire

9

Dow

nstr

eam

ext

ent o

f Urb

an c

atch

men

t. T

ranm

ire

12

Ups

trea

m s

mal

l rur

al c

atch

men

t with

dow

nstr

eam

urb

an.

Tra

nmire

11

U

pstr

eam

sm

all r

ural

cat

chm

ent w

ith d

owns

trea

m u

rban

cha

nnel

with

in D

onny

broo

k.

Tra

nmire

43

U

rban

cha

nnel

thro

ugh

Cor

k C

ity.

Low

er L

ee

36

Urb

an c

hann

el o

f Gla

shee

n R

iver

. Lo

wer

Lee

39

C

atch

men

t of T

wop

ot R

iver

, ext

ends

dow

nstr

eam

to c

onflu

ence

with

Cur

ragh

een.

Lo

wer

Lee

35

D

owns

trea

m e

xten

t of s

ub-c

atch

men

t is

urba

n ar

ea o

f Cor

k, a

nd w

here

Cur

ragh

een

join

s th

e R

iver

Lee

. Lo

wer

Lee

37

U

pstr

eam

sub

-cat

chm

ent w

ith lo

wer

sec

tion

urba

n ch

anne

l. Lo

wer

Lee

38

R

ural

sub

-cat

chm

ent o

f trib

utar

y.

Low

er L

ee

40

Rur

al tr

ibut

ary

catc

hmen

t of C

urra

ghee

n.

Low

er L

ee

52

Sm

all c

atch

men

t with

urb

an e

xten

t at d

owns

trea

m e

nd p

rior

to e

stua

ry.

Car

rigot

hill

51

Sm

all c

atch

men

t with

urb

an e

xten

t at d

owns

trea

m e

nd.

Car

rigot

hill

53

Sm

all r

ural

cat

chm

ent.

Car

rigot

hill

54

Dow

nstr

eam

urb

an c

atch

men

t. C

arrig

othi

ll


Hydrology Report

E4

E2 Integration of hydrology and hydraulic modelling

E2.1 Upper Lee catchment

Figure E1 Catchment map

Table E1 Subcatchment areas

Model Subname Catchment area (km2)

upperlee upperlee1 80.30upperlee upperlee2 96.10upperlee upperlee3 74.33upperlee upperlee4 143.99upperlee upperlee5 88.43upperlee upperlee6 138.08upperlee upperlee7 54.54upperlee upperlee8 116.23

792.00


Hydrology Report

E5

Table E2 1986 and 2006 event data

Fo

r 1

98

6 &

20

06 E

VE

NT

19

03

1 G

au

ge

(T

ota

l c

atc

hm

en

t a

rea

at

ga

ug

e =

up

per

lee

3+

up

pe

r le

e4

= 7

4.3

3+

14

3.9

9 =

21

8.3

2km

2

Are

aF

racti

on

of

1903

1 g

au

ge

Po

int

or

La

tera

l In

flo

wA

pp

lies

at

se

cti

on

(s)

uppe

rlee3

urba

n9.

020.

04la

tera

l5S

UL_

2392

3 to

5S

UL_

2176

9re

mai

ning

rur

al65

.31

0.30

poin

tat

ups

trea

m e

nd w

hich

is 5

SU

L_24

509

uppe

rlee4

urba

n9.

020.

04la

tera

l5S

UL_

6389

to 5

SU

L_33

26F

oher

ish

river

72.7

80.

33po

int

5SU

L_10

247

Riv

er D

ougl

as17

.19

0.08

poin

tat

5S

UL_

2050

1re

mai

ning

rur

al45

.01

0.21

poin

tat

ups

trea

m e

nd w

hich

is 5

SU

L_21

769

1.00

19

02

7 G

au

ge

(T

ota

l c

atc

hm

en

t a

rea

at

ga

ug

e =

up

per

lee

2 =

96.1

0km

2 (

ap

pro

x)

Are

aF

racti

on

of

1902

7 g

au

ge

Po

int

or

La

tera

l In

flo

wA

pp

lies

at

se

cti

on

(s)

uppe

r le

e2al

l rur

al96

1.00

poin

t5S

U1_

1860

1.00

Ca

rrig

ad

roh

id R

es

erv

oir

In

flo

w (

Up

str

ea

m o

ne

of

two

) (T

ota

l c

atc

hm

en

t a

rea

at

dam

=

up

perl

ee

2+

up

perl

ee3+

up

perl

ee4

+u

pp

erl

ee6+

up

perl

ee7+

up

perl

ee

8=

96.1

0+

74

.33+

143.9

9+

138.0

8+

54.5

4+

116.2

3 =

623.2

7km

2 )

Sin

ce u

pper

lee2

, upp

erle

e 3

and

uppe

rlee

4 ar

e gu

aged

, the

se fl

ows

need

to b

e su

btra

cted

from

Tot

al U

pstr

eam

Res

ervo

ir In

flow

to g

et fl

om fr

om 6

, 7 ,8

.N

et U

pstr

eam

Res

ervo

ir In

flow

= T

otal

Ups

trea

m R

eser

voir

Inflo

w -

Flo

w a

t Gau

ge 1

9027

- G

auge

Flo

w a

t 190

31

(Rem

aini

ng C

atch

men

t Are

a =

upp

erle

e6+u

pper

lee7

+up

perle

e8=

138.

08+

54.5

4+11

6.23

=30

8.85

km2 )

Are

aF

racti

on

of

Net U

ps

trea

m R

ese

rvo

ir I

nfl

ow

Po

int

or

La

tera

l In

flo

wA

pp

lies

at

se

cti

on

(s)

uppe

r le

e 7

rem

aini

ng r

ural

31.3

00.

10po

int

at 5

ULE

_532

84ur

ban

3.91

0.01

late

ral

betw

een

5ULE

_532

84 a

nd 5

ULE

_514

83B

unns

heel

in r

iver

19.3

40.

06po

int

at 5

UL1

_924

uppe

r le

e 8

urba

n5.

110.

02la

tera

lbe

twee

n 5U

LE_4

3617

and

5U

LE_4

2311

Bea

laph

adee

n st

ream

19.5

50.

06po

int

5ULE

_493

04A

ghna

kinn

eirt

h st

ream

12.1

70.

04po

int

5ULE

_465

87Lo

ugh

allu

a24

.54

0.08

poin

t5U

LE_5

1483

Rem

aini

ng R

ural

54.8

70.

18po

int

5ULE

_423

11

uppe

r le

e 6

toon

riv

er49

.35

0.16

poin

t5U

LE_2

8238

Bui

ngea

riv

er35

.81

0.12

poin

t5U

LE_2

1690

rem

aini

ng r

ural

52.9

20.

17po

int

5ULE

_335

921.

00


Hydrology Report

E6

Inis

hc

arr

a R

es

erv

oir

(D

ow

ns

tre

am

on

e o

f tw

o)

(To

tal

ca

tch

men

t are

a a

t d

am

= u

pp

erl

ee1

+u

pp

erl

ee2

+u

pp

erl

ee3

+u

pp

erl

ee

4+

up

pe

rlee

5+

up

pe

rlee

6

.+u

pp

erl

ee7

+u

pp

erl

ee8

= 8

0.3

0+

96.1

0+

74

.33+

143

.99+

88.4

3+

13

8.0

8+

54

.54+

116

.23 =

792

.00

km

2 )

Tot

al r

eser

voir

inflo

w n

eeds

to b

e sp

lit b

etw

een

upst

ream

end

and

upp

er le

e 1

catc

hmen

t

Fra

cti

on

of

Do

wn

str

ea

m r

es

erv

oir

In

flo

wP

oin

t o

r L

ate

ral

Infl

ow

Ap

pli

es

at

se

cti

on

(s)

upst

ream

end

0.90

poin

t5U

LE_1

6029

uppe

r le

e 1

0.10

poin

t5U

LE1_

2973

1.00

Ch

ec

k P

ea

k f

low

fo

r 19

86

even

t, f

or

Carr

igad

roh

id R

ese

rvo

ir:

Pea

k F

low

(m

3s

-1)

1903

1 (M

acro

on)

Gau

ge17

4.85

Not

e: E

stim

ated

1902

7 (S

hana

kill)

Gau

ge95

.50

Car

rigad

rohi

d R

eser

voir

Inflo

w57

2.40

Inni

scar

ra R

eser

voir

Inflo

w50

0.64

Bas

ed o

n C

atch

men

t are

a, w

e w

ould

exp

ect:

1903

1 =

218.

32/6

23.2

7 =

35%

of C

arrig

adro

hid

Res

ervo

ir In

flow

35%

of 5

72.4

0 =

200

m3 s-1

Com

pare

d to

an

obse

rved

of 1

74.8

5 m

3 s-1 T

here

fore

pea

ks a

re in

a r

easo

nabl

e pr

opor

tion

1902

7 =

96.1

0/62

3.27

= 1

5% o

f Car

rigad

rohi

d R

eser

voir

Inflo

w15

% o

f 527

.40

= 88

m3 s-1

Com

pare

d to

an

obse

rved

of 9

5.50

m3 s-1

The

refo

re p

eaks

are

in a

rea

sona

ble

prop

ortio

n


Hydrology Report

E7

Table E3 Design event

Are

aF

rac

tio

n o

f U

pp

er

Le

e 3

Po

int

or

Late

ral In

flo

wA

pp

lies

at

se

cti

on

(s)

Na

me

N

am

e u

sed

in

IS

IS M

od

el

uppe

rlee3

-ur

ban

9.02

0.12

late

ral

5SU

L_23

923

to 5

SU

L_21

769

G1

90

31

_a

G1

90

31

_a

rem

aini

ng r

ural

65.3

10.

88po

int

at u

pstr

eam

end

whi

ch is

5S

UL_

2450

9G

19

03

1_

b5S

UL

_2

45

09

74.3

31.

00

Are

aF

rac

tio

n o

f U

pp

er

Le

e 4

Po

int

or

Late

ral In

flo

wA

pp

lies

at

se

cti

on

(s)

Na

me

N

am

e u

sed

in

IS

IS M

od

el

uppe

rlee4

urba

n9.

020.

06la

tera

l5S

UL_

6389

to 5

SU

L_33

26G

19

031

_c

G1

90

31

_c

Foh

eris

h riv

er72

.78

0.51

poin

t5S

UL_

1024

7G

19

03

1_

dG

19

03

1_

d

Riv

er D

ougl

as17

.19

0.12

poin

tat

5S

UL_

2050

1G

19

031

_e

G1

90

31

_e

rem

aini

ng r

ural

45.0

10.

31po

int

at u

pstr

eam

end

whi

ch is

5S

UL_

2176

9G

19

031

_f

G1

90

31

_f

144

1.00

Are

aF

rac

tio

n o

f U

pp

er

Le

e 2

Po

int

or

Late

ral In

flo

wA

pp

lies

at

se

cti

on

(s)

Na

me

N

am

e u

sed

in

IS

IS M

od

el

uppe

r le

e2al

l rur

al96

1.00

poin

t5S

U1_

1860

G1

90

27

_a

5S

U1_

18

60

96.1

01.

00

Are

aF

rac

tio

n o

f U

pp

er

Le

e 7

Po

int

or

Late

ral In

flo

wA

pp

lies

at

se

cti

on

(s)

Na

me

N

am

e u

sed

in

IS

IS M

od

el

uppe

r le

e 7

rem

aini

ng r

ural

31.3

00.

57po

int

at 5

ULE

_532

84C

RI_

a5U

LE

_5

32

84

urba

n3.

910.

07la

tera

lbe

twee

n 5U

LE_5

3284

and

5U

LE_5

1483

CR

I_b

CR

I_b

Bun

nshe

elin

riv

er19

.34

0.35

poin

tat

5U

L1_9

24C

RI_

c5

UL

1_

924

551.

00

Are

aF

rac

tio

n o

f U

pp

er

Le

e 8

Po

int

or

Late

ral In

flo

wA

pp

lies

at

se

cti

on

(s)

Na

me

N

am

e u

sed

in

IS

IS M

od

el

uppe

r le

e 8

urba

n5.

110.

04la

tera

lbe

twee

n 5U

LE_4

3617

and

5U

LE_4

2311

CR

I_d

CR

I_d

Bea

laph

adee

n st

ream

19.5

50.

17po

int

5ULE

_493

04C

RI_

eC

RI_

e

Agh

naki

nnei

rth

stre

am12

.17

0.10

poin

t5U

LE_4

6587

CR

I_f

CR

I_f

Loug

h al

lua

24.5

40.

21po

int

5ULE

_514

83C

RI_

gC

RI_

g

Rem

aini

ng R

ural

54.8

70.

47po

int

5ULE

_423

11C

RI_

hC

RI_

h

116

1.00

Are

aF

rac

tio

n o

f U

pp

er

Le

e 9

Po

int

or

Late

ral In

flo

wA

pp

lies

at

se

cti

on

(s)

Na

me

N

am

e u

sed

in

IS

IS M

od

el

uppe

r le

e 6

Too

n riv

er49

.35

0.36

poin

t5U

LE_2

8238

CR

I_i

CR

I_i

Bui

ngea

riv

er35

.81

0.26

poin

t5U

LE_2

1690

CR

I_j

CR

I_j

rem

aini

ng r

ural

52.9

20.

38po

int

5ULE

_335

92C

RI_

kC

RI_

k

138

1.00

Are

aF

rac

tio

n o

f U

pp

er

Le

e 5

Po

int

or

Late

ral In

flo

wA

pp

lies

at

se

cti

on

(s)

Na

me

N

am

e u

sed

in

IS

IS M

od

el

uppe

r le

e 5

rura

l88

.43

1.00

poin

t5U

LE_1

6029

IRI_

aIR

I_a

88.4

31.

00

Are

aF

rac

tio

n o

f U

pp

er

Le

e 1

Po

int

or

Late

ral In

flo

wA

pp

lies

at

se

cti

on

(s)

Na

me

N

am

e u

sed

in

IS

IS M

od

el

uppe

r le

e 1

rura

l80

.30

1.00

poin

t5U

LE1_

2973

IRI_

b5U

LE

1_

29

73

80.3

01.

00

Tra

nsfe

r fr

om C

arrig

adro

hid

Res

ervo

ir to

Inni

scar

ra R

eser

voir

Are

aF

rac

tio

n o

f C

arr

iga

dro

hid

Re

se

rvo

ir O

utf

low

Po

int

or

Late

ral In

flo

wA

pp

lies

at

se

cti

on

(s)

Na

me

N

am

e u

sed

in

IS

IS M

od

el

1.00

5ULE

_160

29U

IRI_

cIR

I_c

-1.

00T

his

boun

dary

doe

sn't

need

to b

e in

clud

ed in

the

IED

file

s. IR

I_c

will

sim

ply

be a

n A

bstr

actio

n U

nit,

whi

ch w

ill u

se L

ogic

al R

ules

, w

here

Log

ical

Rul

es s

tate

, Flo

w(I

RI_

c) =

Flo

w(C

arD

amU

S)


Hydrology Report

E8

E2.2 Owennacurra catchment

Figure E2 Catchment map

FigureE3 October 2004 rainfall contours


Hydrology Report

E9

Figure E4 November 2000 rainfall contours

Table E4 Average rainfall for 2000 and 2004 events

Model Subname Catchment area (km2) Fraction of total catchment (-) Average rainfall Oct 2004 (mm) Average rainfall Nov 2000 (mm)

owennacurra Owen1 73.92 43.53 75.00 48.00owennacurra Owen2 32.26 19.00 80.00 44.00owennacurra Owen3 36.94 21.75 73.00 48.00owennacurra Owen4 5.56 3.27 69.00 42.00owennacurra Owen5 9.88 5.82 70.00 43.00owennacurra Owen6 11.27 6.64 67.00 41.00

169.83

Table E5 Owennacurra model inflow details

Model Subname

Subcatcment

area (km2)

Percentage of total sub-

catchment Cross section connection Type of inflow

owennacurra Owen1 73.92 100 3OWE_8132 Point

owennacurra Owen2 5.21 16 3OWE_7453 Point

owennacurra 21.90 68 3OWE_5001 Point

owennacurra 5.15 16 3OWE_4966 to 3OWE_2088 Lateral

owennacurra Owen3 36.94 100 3DU1_3244 Point

owennacurra Owen4 4.01 72 3DUN_2235 Point

owennacurra 1.55 28 3DUN_1331 to 3DUN_0 Lateral

owennacurra Owen5 9.88 100 3DU2_1520 Point

owennacurra Owen6 11.27 100 3OWE_2088 to 3OWE_0 Lateral


Hydrology Report

E10

Table E6 Scaling factors for the catchment for calibration, verification and design events.

Main calibration event Verification event Design eventsOct-04 Nov-00 Oct-04 Nov-00 Design flows

Model Subname

Scaling of flow (based on

rainfall)

Scaling of flow

(based on rainfall) Scaling of flow for model input Scaling of flow for model input Scaling of flow for model input

owennacurra Owen1 1.00 1.00 1.00 1.00 1.00


owennacurra 1.07 0.92 0.32 0.30 0.68

owennacurra 1.07 0.92 0.07 0.07 0.16



owennacurra 0.92 0.88 0.02 0.02 0.28



E2.3 Owenboy catchment

Table E7 Owenboy subcatchment areas and fractions

For 2002 & 2004 EVENT

19001 gaugeName Cross_sect Area (km²) Fraction of gauged flow (-)

1BO2_F 1BO2_3257 4.2 0.04 1BOY=main river inflows1BO3_F 1BO3_480 6.4 0.06 1BO2, 3, .., 7 = tributary inflows1BO4_F 1BO4_413 2.3 0.021BO5_F 1BO5_649 2.1 0.021BO7_F 1BO7_1245 3.0 0.031BOY_F01 1BOY_23267 35.0 0.341BOY_F02 1BOY_19051 20.6 0.201BOY_F03 1BOY_11066 18.5 0.181BOY_F04 1BOY_5454 11.1 0.111BOY_F05 25.7Total 103.2 1.00

Total from area upstream of gauge 103.3


Hydrology Report

E11

E2.4 Glashaboy catchment

Figure E5 Glashaboy catchment

Table E8 Glashaboy subcatchment areas and fractions

Model Subname Catchment area (km2) Fraction of total catchment (-)

glashaboy glash1 38.19 0.26glashaboy glash2 37.93 0.26glashaboy glash3 43.68 0.30glashaboy glash4 19.44 0.13glashaboy glash5 5.88 0.04

145.12

Table E9 Glashaboy model inflow details

Model Subname

Fraction of total

catchment (-)

Percentage of total sub-

catchment flow Cross section connection Type of inflow

glashaboy glash1 0.26 100 4GLA_15642 Pointglashaboy glash2 0.03 12 4GLA_12960 Pointglashaboy glash2 0.14 53 4GLA_9707 Pointglashaboy glash2 0.02 6 4GLA_8994 Pointglashaboy glash2 0.02 9 4GLA_7912 Pointglashaboy glash2 0.02 9 4GLA_6882 Pointglashaboy glash2 0.03 11 4GLA_5405 to 4GLA_3138 Lateralglashaboy glash3 0.30 100 4BUT_1284 Pointglashaboy glash4 0.13 100 4BUT_416 Pointglashaboy glash5 0.04 100 4GLA_3138 to 4GLA_0 Lateral


Hydrology Report

E12

E2.5 Bride catchment


Table E10 Bride subcatchment areas and fractions

Model Subname

Catchment area

(km2)Fraction of total

catchment (-)

Bride bride1 20.16 48.37Bride bride2 12.50 29.99Bride bride3 9.02 21.64

41.68

Table E11 Bride model inflow details

Design flows

Model Subname

Subcatcment area

(km2)Percentage of total

sub-catchment Cross section connection Type of inflow

Scaling of sub-catchment flow

for model input

Bride bride1 15.25 76 7BR1_3361 Point 0.76

bride1 4.91 24 7BR1_1968 Point 0.24

Bride bride2 4.13 33 7BRI_8655 Point 0.33

bride2 4.71 38 7BRI_5556 Point 0.38

bride2 3.66 29 7BRI_2306 to 7BRI_0 Lateral 0.29

Bride bride3 9.02 100 7BR2_3753 to 7BR2_0 Lateral 1.00


Hydrology Report

E13

E2.6 Carrigtohill catchment


Table E12 Carrigtohill subcatchment areas and fractions


Carrigtohill carig1 8.36 37.85Carrigtohill carig2 6.98 31.60Carrigtohill carig3 5.44 24.63Carrigtohill carig4 1.31 5.93

22.09

Table E13 Carrigtohill model inflow details

Design flows

Model Subname

Subcatcment

area (km2)Percentage of total


Scaling of sub-catchment

flow for model input

Carrigtohill carig1 8.08 97 2CA2_1395 Point 0.97

Carrigtohill carig1 0.28 3 2CA2_1395 to 2CA2_809 Lateral 0.03

Carrigtohill carig2 6.26 90 2CA1_1396 Point 0.90


Carrigtohill carig3 5.44 100 2CAR_1800 Point 1.00

Carrigtohill carig4 0.88 67 2CAR_1654 to 2CAR_709 Lateral 0.67


Carrigtohill carig4 0.15 11 2CAR_519 Point 0.11

E2.7 Tramore catchment


Hydrology Report

E14


Table E14 Tramore subcatchment areas and fractions


Tramore tran1 7.63 35.97Tramore tran2 2.10 9.90Tramore tran3 3.39 15.98Tramore tran4 3.51 16.55Tramore tran5 4.58 21.59

21.21

Table E15 Tramore model inflow details

Design flows

Model Subname

Subcatcment area

(km2)Percentage of total sub-

catchment Cross section connection Type of inflow

Scaling of sub-catchment flow

for model input

Tramore tran1 5.41 71 6TRA_3559 to 6TRA_0 Lateral 0.71

tran1 1.28 17 6TRA_1541 Point 0.17

tran1 0.94 12 6DOU_845 to 6DOU_0 Lateral 0.12

Tramore tran2 2.10 100 6TRA_5921 Point 1.00

Tramore tran3 1.59 47 6DOU_2737 Point 0.47

tran3 1.80 53 6DOU_1370 to 6DOU_952 Lateral 0.53

Tramore tran4 3.51 100 6DO1_1014 Point 1.00

Tramore tran5 4.58 100 6TRA_5812 to 6TRA_3623 Lateral 1.00

E2.8 Lower Lee


Hydrology Report

E15

Figure E9 catchment map

November 2002 flood event

Table E16 Average rainfall for November 2002 flood event

Model Subname Catchment area (km2) Fraction of total catchment (-) Average rainfall Nov 2002 (mm)

Lower Lee lowlee1 63.40 15.12 N/ALower Lee lowlee2 70.27 16.75 N/ALower Lee lowlee3 24.48 5.84 N/ALower Lee lowlee4 41.16 9.81 N/ALower Lee lowlee5 8.64 2.06 50.00Lower Lee lowlee6 7.74 1.85 50.00Lower Lee lowlee7 9.54 2.27 45.00Lower Lee lowlee8 6.60 1.57 45.00Lower Lee lowlee9 10.57 2.52 45.00Lower Lee lowlee10 11.91 2.84 45.00Lower Lee lowlee11 62.91 15.00 50.00Lower Lee lowlee12 49.15 11.72 50.00Lower Lee lowlee13 18.57 4.43 60.00Lower Lee lowlee14 19.18 4.57 50.00Lower Lee lowlee15 15.31 3.65 N/A

419.43

Table E17 Lower Lee model inflow details


Hydrology Report

E16

Ga

ug

e 1

90

16

Mo

de

lS

ub

na

me

Su

bcatc

hm

en

t are

a

(km

2)

Perc

en

tag

e o

f to

tal

su

b-

ca

tch

me

nt

Pe

rce

nta

ge

of

tota

l c

atc

hm

en

t

up

str

ea

m o

f 19

01

6C

ross s

ecti

on

co

nn

ecti

on

Typ

e o

f in

flo

w

Sc

alin

g o

f fl

ow

base

d o

n

ga

ug

e

Low

er L

eelo

wle

e1

11.

190.

020.

018R

BR

_0

70

Po

int

0.0

11

low

lee1

119

.05

0.30

0.17

8R

BR

_0

64

Po

int

0.1

70

low

lee1

12.

140.

030.

028R

BR

_0

53

Po

int

0.0

19

low

lee1

112

.12

0.19

0.11

8R

BR

_0

58

Po

int

0.1

08

low

lee1

115

.73

0.25

0.14

8R

BR

_0

48

Po

int

0.1

40

low

lee1

17.

350.

120.

078R

BR

_0

43

Po

int

0.0

66

low

lee1

15.

330.

080.

058

RB

R_03

9 t

o 8

RB

R_0

15

La

tera

l0.0

48

Low

er L

eelo

wle

e1

246

.77

0.95

0.42

8R

BR

_0

80

Po

int

0.4

17

low

lee1

22.

380.

050.

028

RB

R_08

0 t

o 8

RB

R_0

71

La

tera

l0.0

21

Res

erv

oir

ou

tflo

w

Mo

de

lS

ub

na

me

Su

bcatc

hm

en

t are

a

(km

2)

Perc

en

tag

e o

f to

tal

su

b-c

atc

hm

en

tP

erc

en

tag

e o

f to

tal

ca

tch

me

nt

up

str

ea

m o

f 1

90

13

Cro

ss s

ecti

on

co

nn

ecti

on

Typ

e o

f in

flo

w

Sc

alin

g o

f fl

ow

base

d o

n

reserv

oir

ou

tflo

w

Low

er L

eelo

wle

e1

4

uppe

r le

e co

min

g in

to

mod

elN

/AN

/A8L

EE

_1

874

0P

oin

t1.0

00

Ga

ug

e 1

90

15

Mo

de

lS

ub

na

me

Su

bcatc

hm

en

t are

a

(km

2)

Perc

en

tag

e o

f to

tal

su

b-

ca

tch

me

nt

Pe

rce

nta

ge

of

tota

l c

atc

hm

en

t

up

str

ea

m o

f 19

01

5C

ross s

ecti

on

co

nn

ecti

on

Typ

e o

f in

flo

w

Sc

alin

g o

f fl

ow

base

d o

n

ga

ug

e

Low

er L

eelo

wle

e2

70.2

71.

000.

327

8S

HO

_0

57

Po

int

0.3

27

Low

er L

eelo

wle

e4

19.2

70.

470.

090

8S

T1

_00

3P

oin

t0.0

90

low

lee4

19.2

70.

470.

090

8O

WG

_3

968

Po

int

0.0

90

low

lee4

2.62

0.06

0.01

28O

WG

_168

2 t

o 8

OW

G_11

07

La

tera

l0.0

12

Low

er L

eelo

wle

e1

62.4

40.

980.

291

8M

AR

_03

3P

oin

t0.2

91

low

lee1

0.96

0.02

0.00

48

MA

R_02

5 t

o 8

MA

R_0

08

La

tera

l0.0

04

Low

er L

eelo

wle

e3

7.68

0.31

0.03

68B

LA

_86

25

Po

int

0.0

36

low

lee3

2.72

0.11

0.01

38B

LA

_78

70

Po

int

0.0

13

low

lee3

6.30

0.26

0.02

98B

LA

_50

55

Po

int

0.0

29

low

lee3

6.33

0.26

0.02

98B

LA

_41

28

Po

int

0.0

29

low

lee3

1.45

0.06

0.00

78B

LA

_22

73

Po

int

0.0

07

Low

er L

eelo

wle

e1

50.

510.

030.

002

8M

AR

_00

7 t

o 8

MA

R_0

01

La

tera

l0.0

02

low

lee1

51.

800.

120.

008

8B

LA

_189

6 t

o 8

BL

A_

0L

ate

ral

0.0

08

low

lee1

53.

970.

260.

018

8S

HO

_04

3 t

o 8

SH

O_0

26

La

tera

l0.0

18

low

lee1

50.

370.

020.

002

8S

H1

_00

4 t

o 8

SH

1_0

01

La

tera

l0.0

02

low

lee1

57.

230.

470.

034

8O

WG

_79

3P

oin

t0.0

34

low

lee1

51.

430.

09N

/A8S

HO

_0

14

Po

int

0.0

93

214.

62


Hydrology Report

E17

Sca

led

fro

m g

au

ge 1

90

16

Mo

de

lS

ub

na

me

Su

bcatc

hm

en

t are

a

(km

2)

Perc

en

tag

e o

f to

tal

su

b-

ca

tch

me

nt

Cro

ss s

ecti

on

co

nn

ecti

on

Typ

e o

f in

flo

w

Sca

lin

g o

f fl

ow

(ba

sed

on

rain

fall)

Sca

lin

g o

f fl

ow

fo

r m

od

el

inp

ut

Low

er L

eelo

wle

e5

8.21

0.95

8C

UR

_7

769

to

8C

UR

_12

58

La

tera

l1.

000.0

73

low

lee5

0.43

0.05

8C

U1

_50

5 t

o 8

CU

1_

0L

ate

ral

1.00

0.0

04

Low

er L

eelo

wle

e6

7.25

0.94

8G

LA

_356

6 t

o 8

GL

A_70

La

tera

l1.

000.0

65

low

lee6

0.49

0.06

8S

OU

_3

472

to

8S

OU

_23

05

La

tera

l1.

000.0

04

Low

er L

eelo

wle

e7

6.26

0.66

8C

UR

_9

59

9P

oin

t0.

900.0

50

low

lee7

1.79

0.19

8C

U3_

003

Po

int

0.90

0.0

14

low

lee7

1.49

0.16

8C

UR

_9

197

to

8C

UR

_77

69

La

tera

l0.

900.0

12

Low

er L

eelo

wle

e8

5.50

0.83

8C

U1

_34

08

Po

int

0.90

0.0

44

low

lee8

1.10

0.17

8C

U4_

002

Po

int

0.90

0.0

09

Low

er L

eelo

wle

e9

10.5

71.

008

TW

O_8

65

Po

int

0.90

0.0

85

Low

er L

eelo

wle

e1

011

.91

1.00

8C

U2_

006

Po

int

0.90

0.0

96

Low

er L

eelo

wle

e1

36.

140.

338L

EE

_9

725

to

8L

EE

_53

07

La

tera

l1.

200.0

66

low

lee1

35.

730.

318L

EE

_5

150

to

8L

EE

_17

82

La

tera

l1.

200.0

61

low

lee1

32.

490.

138S

OU

_3

65

9 t

o 8

SO

U_0

La

tera

l1.

200.0

27

low

lee1

34.

210.

238L

EE

_1

67

3 t

o 8

LE

E_0

La

tera

l1.

200.0

45

Low

er L

eelo

wle

e1

43.

4317

.88

8R

BR

_01

5P

oin

t1.

000.0

31

low

lee1

41.

839.

548L

EE

_17

024

Po

int

1.00

0.0

16

low

lee1

44.

8125

.08

8R

BR

_0

15

to

8R

BR

_00

1 a

nd

8L

EE

_15

466

to

8L

EE

_14

774

La

tera

l1.

000.0

43

low

lee1

42.

1811

.37

8B

AL

_2

825

to

8B

AL

_0

La

tera

l1.

000.0

19

low

lee1

42.

3011

.99

8L

EE

_14

715

to

8L

EE

_12

009

La

tera

l1.

000.0

21

low

lee1

41.

859.

658

LE

E_

119

28 t

o 8

LE

E_

992

1L

ate

ral

1.00

0.0

17


Hydrology Report

E18

October 2004 flood event

Table E18 Average rainfall for the October 2004 event

Model Subname Catchment area (km2) Fraction of total catchment (-) Average rainfall Oct 2004 (mm)

Lower Lee lowlee1 63.40 15.12 80.00Lower Lee lowlee2 70.27 16.75 80.00Lower Lee lowlee3 24.48 5.84 90.00Lower Lee lowlee4 41.16 9.81 70.00Lower Lee lowlee5 8.64 2.06 60.00Lower Lee lowlee6 7.74 1.85 65.00Lower Lee lowlee7 9.54 2.27 60.00Lower Lee lowlee8 6.60 1.57 60.00Lower Lee lowlee9 10.57 2.52 50.00Lower Lee lowlee10 11.91 2.84 55.00Lower Lee lowlee11 62.91 15.00 80.00Lower Lee lowlee12 49.15 11.72 80.00Lower Lee lowlee13 18.57 4.43 95.00Lower Lee lowlee14 19.18 4.57 60.00Lower Lee lowlee15 15.31 3.65 80.00

419.43


Hydrology Report

E19


Ga

ug

e 1

90

16

Mo

de

lS

ub

na

me

Su

bc

atc

hm

en

t a

rea

(km

2)

Pe

rce

nta

ge o

f to

tal s

ub

-

ca

tch

me

nt

Pe

rce

nta

ge

of

tota

l ca

tch

me

nt

up

str

ea

m o

f 19

01

6C

ros

s s

ec

tio

n c

on

ne

cti

on

Typ

e o

f in

flo

w

Sca

lin

g o

f fl

ow

ba

sed

on

ga

ug

e

Low

er L

eelo

wle

e1

11.

190.

020.

018

RB

R_

07

0P

oin

t0

.01

1

low

lee

11

19.0

50.

300.

178

RB

R_

06

4P

oin

t0

.17

0

low

lee

11

2.14

0.03

0.02

8R

BR

_05

3P

oin

t0

.01

9

low

lee

11

12.1

20.

190.

118

RB

R_

05

8P

oin

t0

.10

8

low

lee

11

15.7

30.

250.

148

RB

R_

04

8P

oin

t0

.14

0

low

lee

11

7.35

0.12

0.07

8R

BR

_04

3P

oin

t0

.06

6

low

lee

11

5.33

0.08

0.05

8R

BR

_0

39

to

8R

BR

_0

15

La

tera

l0

.04

8

Low

er L

eelo

wle

e1

246

.77

0.95

0.42

8R

BR

_08

0P

oin

t0

.41

7lo

wle

e1

22.

380.

050.

028

RB

R_

080

to

8R

BR

_0

71

La

tera

l0

.02

1

Re

se

rvo

ir o

utf

low

Mo

de

lS

ub

na

me

Su

bc

atc

hm

en

t a

rea

(km

2)

Pe

rce

nta

ge o

f to

tal s

ub

-

ca

tch

me

nt

Pe

rce

nta

ge

of

tota

l ca

tch

me

nt

up

str

ea

m o

f 19

01

3C

ros

s s

ec

tio

n c

on

ne

cti

on

Typ

e o

f in

flo

w

Sca

lin

g o

f fl

ow

ba

sed

on

rese

rvo

ir o

utf

low

Low

er L

eelo

wle

e1

4

Rep

rese

nts

flow

from

up

per

lee

com

ing

into

m

odel

N/A

N/A

8L

EE

_18

74

0P

oin

t1

.00

0


Hydrology Report

E20

Sc

ale

d f

rom

ga

ug

e 1

901

6

Mo

de

lS

ub

na

me

Su

bc

atc

hm

en

t a

rea

(km

2)

Pe

rce

nta

ge o

f to

tal s

ub

-

ca

tch

me

nt

Cro

ss

se

cti

on

co

nn

ec

tio

nT

yp

e o

f in

flo

w

Sca

lin

g o

f fl

ow

(b

as

ed

on

rain

fall

)

Sc

ali

ng

of

flo

w f

or

mo

de

l

inp

ut

Low

er L

eelo

wle

e5

8.21

0.95

8C

UR

_7

76

9 t

o 8

CU

R_

12

58

La

tera

l0.

750

.05

5

low

lee

50.

430.

058

CU

1_

50

5 t

o 8

CU

1_

0L

ate

ral

0.75

0.0

03

Low

er L

eelo

wle

e6

7.25

0.94

8G

LA

_3

56

6 t

o 8

GL

A_

70

La

tera

l0.

810

.05

3

low

lee

60.

490.

068S

OU

_3

47

2 t

o 8

SO

U_

23

05

La

tera

l0.

810

.00

4

Low

er L

eelo

wle

e7

6.26

0.66

8C

UR

_95

99

Po

int

0.75

0.0

42

low

lee

71.

790.

198

CU

3_

00

3P

oin

t0.

750

.01

2

low

lee

71.

490.

168C

UR

_9

19

7 t

o 8

CU

R_

77

69

La

tera

l0.

750

.01

0

Low

er L

eelo

wle

e8

5.50

0.83

8C

U1

_34

08

Po

int

0.75

0.0

37

low

lee

81.

100.

178

CU

4_

00

2P

oin

t0.

750

.00

7

Low

er L

eelo

wle

e9

10.5

71.

008T

WO

_8

65

Po

int

0.63

0.0

59

Low

er L

eelo

wle

e1

011

.91

1.00

8C

U2

_0

06

Po

int

0.69

0.0

73

Low

er L

eelo

wle

e1

36.

140.

338

LE

E_9

72

5 t

o 8

LE

E_5

30

7L

ate

ral

1.19

0.0

65

low

lee

13

5.73

0.31

8L

EE

_5

15

0 t

o 8

LE

E_1

78

2L

ate

ral

1.19

0.0

61

low

lee

13

2.49

0.13

8S

OU

_36

59

to

8S

OU

_0

La

tera

l1.

190

.02

6

low

lee

13

4.21

0.23

8L

EE

_16

73

to

8L

EE

_0

La

tera

l1.

190

.04

5

Low

er L

eelo

wle

e1

43.

4317

.88

8R

BR

_0

15

Po

int

0.75

0.0

23

low

lee

14

1.83

9.54

8L

EE

_1

70

24

Po

int

0.75

0.0

12

low

lee

14

4.81

25.0

88

RB

R_

01

5 t

o 8

RB

R_

00

1 a

nd

8L

EE

_1

54

66

to

8L

EE

_14

77

4L

ate

ral

0.75

0.0

32

low

lee

14

2.18

11.3

78

BA

L_

28

25

to

8B

AL

_0

La

tera

l0.

750

.01

5

low

lee

14

2.30

11.9

98

LE

E_1

47

15

to

8L

EE

_1

20

09

La

tera

l0.

750

.01

5

low

lee

14

1.85

9.65

8L

EE

_1

192

8 t

o 8

LE

E_

99

21

La

tera

l0.

750

.01

2

Low

er L

eelo

wle

e2

70.2

71.

008

SH

O_

05

7P

oin

t1.

000

.62

7

Low

er L

eelo

wle

e4

19.2

70.

478

ST

1_0

03

Po

int

0.88

0.1

50

low

lee

419

.27

0.47

8O

WG

_3

96

8P

oin

t0.

880

.15

0

low

lee

42.

620.

068

OW

G_1

68

2 t

o 8

OW

G_1

10

7L

ate

ral

0.88

0.0

20

Low

er L

eelo

wle

e1

62.4

40.

988

MA

R_0

33

Po

int

1.00

0.5

57

low

lee

10.

960.

028

MA

R_

02

5 t

o 8

MA

R_

00

8L

ate

ral

1.00

0.0

09

Low

er L

eelo

wle

e3

7.68

0.31

8B

LA

_8

62

5P

oin

t1.

130

.07

7

low

lee

32.

720.

118

BL

A_

78

70

Po

int

1.13

0.0

27

low

lee

36.

300.

268

BL

A_

50

55

Po

int

1.13

0.0

63

low

lee

36.

330.

268

BL

A_

41

28

Po

int

1.13

0.0

64

low

lee

31.

450.

068

BL

A_

22

73

Po

int

1.13

0.0

15

Low

er L

eelo

wle

e1

50.

510.

038

MA

R_

00

7 t

o 8

MA

R_

00

1L

ate

ral

1.00

0.0

05

low

lee

15

1.80

0.12

8B

LA

_18

96

to

8B

LA

_0

La

tera

l1.

000

.01

6

low

lee

15

3.97

0.26

8S

HO

_0

43

to

8S

HO

_02

6L

ate

ral

1.00

0.0

35

low

lee

15

0.37

0.02

8S

H1_

00

4 t

o 8

SH

1_0

01

La

tera

l1.

000

.00

3

low

lee

15

7.23

0.47

8O

WG

_7

93

Po

int

1.00

0.0

65

low

lee

15

1.43

0.09

8S

HO

_0

14

Po

int

1.00

0.0

13


Hydrology Report

E21

December 2006


Gau

ge

190

16

Mo

de

lS

ub

nam

e

Su

bc

atc

hm

en

t a

rea

(km

2)

Pe

rce

nta

ge

of

tota

l s

ub

-

ca

tch

me

nt

Pe

rce

nta

ge

of

tota

l c

atc

hm

en

t u

ps

tre

am

of

19

01

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ross s

ec

tio

n c

on

ne

cti

on

Typ

e o

f in

flo

w

Sc

ali

ng

of

flo

w b

as

ed

on

ga

ug

e

Low

er L

eelo

wle

e1

11.

190.

020.

018R

BR

_0

70

Po

int

0.0

11

low

lee1

119

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0.30

0.17

8R

BR

_0

64

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int

0.1

70

low

lee1

12.

140.

030.

028R

BR

_0

53

Po

int

0.0

19

low

lee1

112

.12

0.19

0.11

8R

BR

_0

58

Po

int

0.1

08

low

lee1

115

.73

0.25

0.14

8R

BR

_0

48

Po

int

0.1

40

low

lee1

17.

350.

120.

078R

BR

_0

43

Po

int

0.0

66

low

lee1

15.

330.

080.

058R

BR

_03

9 t

o 8

RB

R_0

15

La

tera

l0

.048

Low

er L

eelo

wle

e1

246

.77

0.95

0.42

8R

BR

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80

Po

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17

low

lee1

22.

380.

050.

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BR

_08

0 t

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RB

R_0

71

La

tera

l0

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Res

erv

oir

ou

tflo

w

Mo

de

lS

ub

nam

e

Su

bc

atc

hm

en

t a

rea

(km

2)

Pe

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nta

ge

of

tota

l s

ub

-

ca

tch

me

nt

Pe

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nta

ge

of

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ps

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on

ne

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on

Typ

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f in

flo

w

Sc

ali

ng

of

flo

w b

as

ed

on

reserv

oir

ou

tflo

w

Low

er L

eelo

wle

e1

4

Rep

rese

nts

flow

from

up

per

lee

com

ing

into

m

odel

N/A

N/A

8L

EE

_18

740

Po

int

1.0

00

Gau

ge

190

15

Mo

de

lS

ub

nam

e

Su

bc

atc

hm

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t a

rea

(km

2)

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of

tota

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-

ca

tch

me

nt

Pe

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nta

ge

of

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atc

hm

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of

19

01

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ec

tio

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on

ne

cti

on

Typ

e o

f in

flo

w

Sc

ali

ng

of

flo

w b

as

ed

on

ga

ug

e

Low

er L

eelo

wle

e2

70.2

71.

000.

327

8S

HO

_0

57

Po

int

0.3

27

Low

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wle

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19.2

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low

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8O

WG

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68

Po

int

0.0

90

low

lee4

2.62

0.06

0.01

28O

WG

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2 t

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G_

11

07

La

tera

l0

.012

Low

er L

eelo

wle

e1

62.4

40.

980.

291

8M

AR

_03

3P

oin

t0

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low

lee1

0.96

0.02

0.00

48M

AR

_02

5 t

o 8

MA

R_0

08

La

tera

l0

.004

Low

er L

eelo

wle

e3

7.68

0.31

0.03

68B

LA

_8

62

5P

oin

t0

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low

lee3

2.72

0.11

0.01

38B

LA

_7

87

0P

oin

t0

.013

low

lee3

6.30

0.26

0.02

98B

LA

_5

05

5P

oin

t0

.029

low

lee3

6.33

0.26

0.02

98B

LA

_4

12

8P

oin

t0

.029

low

lee3

1.45

0.06

0.00

78B

LA

_2

27

3P

oin

t0

.007

Low

er L

eelo

wle

e1

50.

510.

030.

002

8M

AR

_00

7 t

o 8

MA

R_0

01

La

tera

l0

.002

low

lee1

51.

800.

120.

008

8B

LA

_18

96

to

8B

LA

_0

La

tera

l0

.008

low

lee1

53.

970.

260.

018

8S

HO

_04

3 t

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SH

O_0

26

La

tera

l0

.018

low

lee1

50.

370.

020.

002

8S

H1

_00

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o 8

SH

1_0

01

La

tera

l0

.002

low

lee1

57.

230.

470.

034

8O

WG

_7

93

Po

int

0.0

34

low

lee1

51.

430.

09N

/A8S

HO

_0

14

Po

int

0.0

93


Hydrology Report

E22

Sc

ale

d f

rom

ga

ug

e 1

90

16

Mo

del

Su

bn

am

e

Su

bc

atc

hm

en

t a

rea

(km

2)

Perc

en

tag

e o

f to

tal

su

b-

catc

hm

en

tC

ros

s s

ec

tio

n c

on

ne

cti

on

Typ

e o

f in

flo

w

Sc

ali

ng

of

flo

w (

bas

ed

on

rain

fall)

Sca

lin

g o

f fl

ow

fo

r m

od

el

inp

ut

Low

er L

eelo

wle

e5

8.21

0.95

8C

UR

_7

76

9 t

o 8

CU

R_

12

58

La

tera

l1.

000.0

73

low

lee5

0.43

0.05

8C

U1

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5 t

o 8

CU

1_

0L

ate

ral

1.00

0.0

04

Low

er L

eelo

wle

e6

7.25

0.94

8G

LA

_3

56

6 t

o 8

GL

A_

70

La

tera

l1.

000.0

65

low

lee6

0.49

0.06

8S

OU

_3

47

2 t

o 8

SO

U_

23

05

La

tera

l1.

000.0

04

Low

er L

eelo

wle

e7

6.26

0.66

8C

UR

_95

99

Po

int

1.00

0.0

56

low

lee7

1.79

0.19

8C

U3

_0

03

Po

int

1.00

0.0

16

low

lee7

1.49

0.16

8C

UR

_9

19

7 t

o 8

CU

R_

77

69

La

tera

l1.

000.0

13

Low

er L

eelo

wle

e8

5.50

0.83

8C

U1

_34

08

Po

int

1.00

0.0

49

low

lee8

1.10

0.17

8C

U4

_0

02

Po

int

1.00

0.0

10

Low

er L

eelo

wle

e9

10.5

71.

008T

WO

_8

65

Po

int

1.00

0.0

94

Low

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eelo

wle

e10

11.9

11.

008C

U2

_0

06

Po

int

1.00

0.1

06

Low

er L

eelo

wle

e13

6.14

0.33

8L

EE

_9

72

5 t

o 8

LE

E_5

30

7L

ate

ral

1.00

0.0

55

low

lee

13

5.73

0.31

8L

EE

_5

15

0 t

o 8

LE

E_1

78

2L

ate

ral

1.00

0.0

51

low

lee

13

2.49

0.13

8S

OU

_36

59

to

8S

OU

_0

La

tera

l1.

000.0

22

low

lee

13

4.21

0.23

8L

EE

_16

73

to

8L

EE

_0

La

tera

l1.

000.0

38

Low

er L

eelo

wle

e14

3.43

17.8

88R

BR

_01

5P

oin

t1.

000.0

31

low

lee

14

1.83

9.54

8L

EE

_1

70

24

Po

int

1.00

0.0

16

low

lee

14

4.81

25.0

88

RB

R_0

15

to

8R

BR

_00

1 a

nd

8L

EE

_1

546

6 t

o 8

LE

E_

147

74

La

tera

l1.

000.0

43

low

lee

14

2.18

11.3

78B

AL

_28

25

to

8B

AL

_0

La

tera

l1.

000.0

19

low

lee

14

2.30

11.9

98

LE

E_

14

71

5 t

o 8

LE

E_1

20

09

La

tera

l1.

000.0

21

low

lee

14

1.85

9.65

8L

EE

_11

92

8 t

o 8

LE

E_

992

1L

ate

ral

1.00

0.0

17


Hydrology Report

E23

Lower Lee model inputs

Table E21 Fraction of subcatchments of total catchment area.


Lower Lee lowlee1 63.40 15.12Lower Lee lowlee2 70.27 16.75Lower Lee lowlee3 24.48 5.84Lower Lee lowlee4 41.16 9.81Lower Lee lowlee5 8.64 2.06Lower Lee lowlee6 7.74 1.85Lower Lee lowlee7 9.54 2.27Lower Lee lowlee8 6.60 1.57Lower Lee lowlee9 10.57 2.52Lower Lee lowlee10 11.91 2.84Lower Lee lowlee11 62.91 15.00Lower Lee lowlee12 49.15 11.72Lower Lee lowlee13 18.57 4.43Lower Lee lowlee14 19.18 4.57Lower Lee lowlee15 15.31 3.65

419.43


Hydrology Report

E24


Design flows

Model Subname

Subcatcment area

(km2)

Percentage of total


Lower Lee lowlee1 62.44 0.98 8MAR_033 Point

lowlee1 0.96 0.02 8MAR_025 to 8MAR_008 Lateral

Lower Lee lowlee2 70.27 1.00 8SHO_057 Point

Lower Lee lowlee3 7.68 0.31 8BLA_8625 Point

lowlee3 2.72 0.11 8BLA_7870 Point




Lower Lee lowlee4 19.27 0.47 8ST1_003 Point

lowlee4 19.27 0.47 8OWG_3968 Point

lowlee4 2.62 0.06 8OWG_1682 to 8OWG_1107 Lateral

Lower Lee lowlee5 8.21 0.95 8CUR_7769 to 8CUR_1258 Lateral

lowlee5 0.43 0.05 8CU1_505 to 8CU1_0 Lateral

Lower Lee lowlee6 7.25 0.94 8GLA_3566 to 8GLA_70 Lateral

lowlee6 0.49 0.06 8SOU_3472 to 8SOU_2305 Lateral

Lower Lee lowlee7 6.26 0.66 8CUR_9599 Point

lowlee7 1.79 0.19 8CU3_003 Point

lowlee7 1.49 0.16 8CUR_9197 to 8CUR_7769 Lateral

Lower Lee lowlee8 5.50 0.83 8CU1_3408 Point

lowlee8 1.10 0.17 8CU4_002 Point

Lower Lee lowlee9 10.57 1.00 8TWO_865 Point

Lower Lee lowlee10 11.91 1.00 8CU2_006 Point

Lower Lee lowlee11 1.19 0.02 8RBR_070 Point

lowlee11 19.05 0.30 8RBR_064 Point





lowlee11 5.33 0.08 8RBR_039 to 8RBR_015 Lateral

Lower Lee lowlee12 46.77 0.95 8RBR_080 Point

lowlee12 2.38 0.05 8RBR_080 to 8RBR_071 Lateral

Lower Lee lowlee13 N/Adesign inflow from

bride model 8LEE_2538 Point

lowlee13 6.14 0.33 8LEE_9725 to 8LEE_5307 Lateral


lowlee13 2.49 0.13 8SOU_3659 to 8SOU_0 Lateral


Lower Lee lowlee14 N/Adesign inflow from

upper lee model 8LEE_18740 Point


lowlee14 2.78 0.14 8LEE_18740 Point

lowlee14 1.83 0.10 8LEE_17024 Point

lowlee14 4.81 0.25

8RBR_015 to 8RBR_001 and

8LEE_15466 to 8LEE_14774 Lateral

lowlee14 2.18 0.11 8BAL_2825 to 8BAL_0 Lateral



Lower Lee lowlee15 0.51 0.03 8MAR_007 to 8MAR_001 Lateral

lowlee15 1.80 0.12 8BLA_1896 to 8BLA_0 Lateral

lowlee15 3.97 0.26 8SHO_043 to 8SHO_026 Lateral

lowlee15 0.37 0.02 8SH1_004 to 8SH1_001 Lateral

lowlee15 7.23 0.47 8OWG_793 Point

lowlee15 1.43 0.10 8SHO_013 Point


Hydrology Report

F1

Appendix F. Future drivers of flood risk


Hydrology Report

F2

F1 Climate change literature review

Intergovernmental Panel on Climate Change (IPCC)

IPCC 4th Assessment report (2007)

The IPCC 4th Assessment report culminates the past six years of world wide scientific and technical literature published on climate change, its potential impacts and possible mitigation/adaptation options. The report states “Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely (assessed likelihood >90%) due to the observed increase in anthropogenic greenhouse gas concentrations. For the next two decades a warming of about 0.2°C per decade is projected for a range of future greenhouse gas (GHG) emission scenarios. Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected. A number of different scenarios are available to estimate what emissions might be expected in the future, encompassing a range of probable economic, political, population and technological developments in the next century. The best estimate of projected changes in mean global temperature for the end of this century range from 1.8 to 4°C, depending on the emissions scenario used.

It is very likely that heavy precipitation events will continue to become more frequent. Although there is no clear trend in the number of hurricanes occurring, some research suggests very intense storms are becoming more common as the oceans warm.

The report states that global average sea level rose at an average rate of 1.8mm/year (1961-2003) and this rate has accelerated to 3.1mm/year over the past decade (1993-2003). Although, whether the faster rate for 1993-2003 reflects decadal variability or an increase in the longer-term trend is unclear. Projections on globally averaged sea level rise by 2100 for various greenhouse gas emissions range between 0.18m to 0.38m (scenario B1: assuming a best estimate of 1.8°C increase) to between 0.26m to 0.59m (scenario A1FI: assuming a best estimate of 4.0°C increase).

The emission scenarios range from B1 with an emphasis on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives; to A1FI with an emphasis on increased cultural and social interactions, with a substantial reduction in regional differences in per capita income, with the energy system energy fossil intensive. These estimates are based on thermal expansion of ocean water and melting glaciers and ice caps. Beyond 2100, larger changes will occur due to the melting of ice sheets, having consequences on coastal communities and flooding.

Irish Committee on Climate Change – Ireland and the IPCC 4th Assessment Report (2007)

The Community Climate Change Consortium for Ireland (C4I) based at Met Éireann and the Irish Climate Analysis and Research Units (ICARUS) at NUI Maynooth have downscaled the latest climate models to project the impact of climate change in Ireland. In general, most global average predictions will be applicable due to the mid-latitude of the country. The climate will potentially warm slightly faster than the global average over the next few decades, and winter rainfall will increase, predominantly in the west of Ireland. Summer rainfall will decline, predominantly on the east coast.


Hydrology Report

F3

UK Climates Impact Programme 2002 (UKCIP, 2002)

UK

The UKCIP02 (Hulme et al, 2002) publication estimates climate change predictions for a range of parameters for four scenarios of future climate change, known as: High, Medium-high, Medium-Low and Low, relating to different greenhouse gas emissions scenarios. The future predictions are based on three time horizons, 2020, 2050 and 2080.

The findings estimate that UK winters will become wetter and summers drier. Extreme winter precipitation will become more frequent. As global temperature warms, global-average sea level may rise between 23cm and 36cm by the 2080’s. Extreme sea levels, occurring through combinations of high tides, sea level rise and changes in wind will be experienced more frequently in many coastal locations.

Ireland

For Ireland, winter precipitation totals are expected to increase and summer precipitation totals to decrease. The largest percentage changes are in the east and south of Ireland. Winter precipitation is estimated to increase by between 10% (Low and Medium-Low emission scenarios) and 15% by 2080 (Medium-High and High emission scenarios) for the area of Ireland where the Lee catchment is situated. Changes in global average sea level will occur as a consequence of global temperature change. The increase in sea level will be due to thermal expansion of ocean water and through melting of glaciers. It is estimated, dependent on which emissions scenario is adopted, that global average sea level will rise by between 23cm and 36cm by 2080.

The change in the 50-year return period surge height for the 2080s for the area of sea surrounding Cork for three different emissions scenarios is estimated to be 0.1m (Low emissions scenario), 0.3m (Medium-High emissions scenario) and 0.6m (High emissions scenario). This considers the combined effect of global-average sea-level rise, storminess changes and vertical land movements.

Sea-level rise will lead to locally deeper water in the near-shore zone and therefore lead to greater wave energy being transmitted to the shoreline. In addition changes in wind speed will also occur. The 2-year return period daily-average wind speed is estimated to increase by up to 6% for winter in the 2080s, assuming a Medium-high or High emissions scenario.

Implications of the EU Climate Protection Target for Ireland (EPA, 2007)

The European Union (EU) has adopted a long-term climate protection target to limit global mean temperatures to not more than 2°C above pre-industrial levels. This action is in response to the United Nations Framework Convention on Climate Change (UNFCCC) Article 2 objective which is to stabilise “greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system”.

The aim of the recent EPA published report by ICARUS (McElwain and Sweeney, 2007), was to provide an assessment of what the EU 2°C target means for Ireland. Scientific analyses suggest that the rate of temperature increase may be as important as the absolute change. The current rate of global temperature increase of 0.2-0.3°C per decade is already greater than that experienced over the past 10,000 years. A high rate of change can increase the risk of high-impact events.


Hydrology Report

F4

McElwain and Sweeney, highlight that “Ireland will also experience significant climate change impacts below 2°C, many of which are now unavoidable. Adaptation actions will be required to reduce adverse impacts of these changes.” Increased frequency and magnitude of flooding will be a consequence of increasing global mean temperatures, which will have important implications for infrastructure and development on affected flood plains. There will also be impacts on the reliability of existing flood defences, and, in the future, increased insurance costs.

The impact of sea level rise will be most apparent in coastal cities in Ireland, including Cork. The major effect for Cork will be increased risk of flooding both at the coast and along major rivers during storm surge events (Fealy, 2003).

Predictions for future storms are still uncertain; however the theory supporting the drivers for hurricanes strongly suggests that peak intensities would be higher with warmer ocean temperatures.

Statistical downscaling from an ensemble of three Global Climate Models (GCM), project for the end of the present century (2080), an increase in precipitation of between 11% and 17% for winter months (Sweeney and Fealy, 2006).

Climate change impacts can occur in two ways; firstly, linear and smooth, thus relatively predictable, allowing society time to adapt and allowing impacts to be managed. Secondly, abruptly, occurring over timescales from years to decades, with little warning and leaving less time for adaptability.

Regional Climate Model Predictions for Ireland (McGrath et al, 2005)

The Community Climate Change Consortium for Ireland (C4I) project has enabled the establishment of a regional climate modelling facility in Met Éireann, as documented in the C4I Annual Report 2004 (McGrath et al, 2004). A key objective is to develop a new national capacity to forecast future climate conditions in Ireland. This is considered to be necessary for the development of national planning for adaptation to the impacts of projected climate change.

McGrath et al (2005), provides an analysis of future Irish climate conditions for the period 2021–2060 based on the outputs from the Met Éireann Regional Climate Model (RCM) using 1961-2000 as a reference. The Met Éireann RCM improves the understanding of climate change and its implications for Ireland, and quantifies the uncertainties in the climate projections.

The RCM projects temperature changes, which show a general warming in the future period with mean monthly temperatures increasing typically between 1.25 and 1.5°C, the largest increases are seen in the southeast and east, with the greatest warming occurring in July.

For precipitation, the most significant changes occur in the months of June and December; June values show a decrease of about 10% compared with the current climate, noticeably in the southern half of the country; March, July and August are largely unchanged but all other months show overall increases. December values show increases ranging between 10% in the south-east and 25% in the north-west. There is also some evidence of an increase in the frequency of extreme precipitation events (i.e. events which exceed 20 mm or more per day) in the north-west.


Hydrology Report

F5

In the future scenario, the frequency of intense cyclones (storms) over the North Atlantic area in the vicinity of Ireland is increased by about 15% compared with the current climate, with even stronger increases in winter and spring. This is related to the projected general rise in sea surface temperatures.

The impact of climate change predictions on river flooding was modelled under different scenarios using the Suir catchment as a pilot study. The increase in winter precipitation was found to produce a significant increase in the more intense discharge episodes, raising the risk of future flooding in the area. The model predicts an increase in frequency and intensity of heavy discharges e.g. above 350m3/s. The 10 year return period flow increased from 290m3/s to 360m3/s (an increase of 24%). This highlights the implications faced by future planning to reduce impacts of flooding.

It should be noted that the catchment response to rainfall is catchment specific and this will vary catchment to catchment.

Scenarios and Impacts for Ireland (Sweeney et al, 2003)

This report presents an assessment of the magnitude and likely impacts of climate change in Ireland over the course of the current century, based on statistical downscaling of the GCM output from the Hadley Centre model (used in the UKCIP02 study), to project likely changes in Irish climate from the 1961–1990 averages. The results of this analysis suggest that current mean January temperatures in Ireland are predicted to increase by 1.5°C by mid-century with a further increase of 0.5–1.0°C by 2075. By 2055, the extreme south and south-west coasts will have a mean January temperature of 7.5–8.0°C. By then, winter conditions in Northern Ireland and in the north Midlands will be similar to those currently experienced along the south coast. Since temperature is a primary meteorological parameter, secondary parameters such as frost frequency and growing season length and thermal efficiency can be expected to undergo considerable changes over this time interval. July mean temperatures will increase by 2.5°C by 2055 and a further increase of 1.0°C by 2075 can be expected. Mean maximum July temperatures in the order of 22.5°C will prevail generally with areas in the central Midlands experiencing mean maxima up to 24.5°C. Overall increases of 11% in precipitation are predicted for the winter months of December–February. The greatest increases are suggested for the north-west, where increases of approximately 20% are suggested by mid-century. Little change is indicated for the east coast and in the eastern part of the Central Plain. Marked decreases in rainfall during the summer and early autumn months across eastern and central Ireland are predicted. Nationally, these are of the order of 25% with decreases of over 40% in some parts of the east.

Global sea level is projected to rise by approximately 0.5 m by the end of the century, predominantly due to warming and expansion of the ocean water body. In Ireland, this figure will be modified by local land-level changes.

As a general approximation, land retreat of about 1m can be anticipated on sandy coastlines in Ireland for every centimetre rise in sea level. Inundation risk must also take into account storm surge events and high tide frequencies. A value of 2.6m OD Malin for extreme water level presently occurs with a return frequency of 12 years on the west coast and 100 years on the east coast. These return periods of extreme water level are likely to reduce considerably as sea levels rise. Combining these extreme water levels with a sea-level rise of 0.49m places approximately 300km2 of land in Ireland at risk of inundation.


Hydrology Report

F6

In situations where land loss cannot be economically defended, it should not be contemplated. Where infrastructure is at risk of inundation, cost-beneficial solutions may exist. This is particularly the case in the cities of Dublin, Cork, Limerick and Galway, and for assets such as railway lines, airports and power stations.

Foresight (2004)

The Foresight study, undertaken based on the UK (2004) provided a vision for flood and coastal defence in the UK between 2030 and 2100, to inform long-term policy. The study considered four scenarios based on different approaches to governance (centralised versus localised) and different values held by society (consumerist versus community). Various future drivers of flood risk were evaluated, amongst these precipitation, relative sea level rise and surges. It was concluded that climate change has a high impact in all of the four scenarios studied. Relative sea level rise could increase the risk of coastal flooding by 4 to 10 times by 2080. Therefore there could be a change in the frequency of flooding, for example a flood with a current Annual Exceedance Probability (AEP) of 1% could occur with an AEP of between 4% and 10% by 2080. Precipitation will increase risks across the country by 2 to 4 times by 2080, although specific locations could experience changes well outside this range. In addition the increase in surge could increase the risk of coastal flooding by 2 to 10 times (depending on scenario adopted). [Risk is taken to mean: probability x consequences, where consequences relate to people and the natural and built environment].

Projecting future sea level rise (Rahmstorf, 2007)

Due to the complex mechanisms and varying timescales involved, Rahmstorf uses a semi-empirical model of sea-level rise, where a simple linear relationship is developed between observed global sea-level and observed temperature. This is done for the period 1880-2001, which reveals a highly significant correlation with an average rise of 3.4 mm per year. This relationship allows future sea-levels to be explored, given different scenarios of 21st century temperature. Using the IPCC Third Assessment Report scenarios (which span a range of temperature increases from 1.4 to 5.8°C) as input, a best estimate of sea-level rise of 55 to 125cm by 2100 is estimated. These numbers are significantly higher than the model-based estimates of the IPCC, which give a range of 9 to 88cm for the same scenarios, and may have important implications for planning adaptation measures at the coast. Although such an approach makes the assumption that the observed relationship between global temperatures and global sea-level will hold in to the future, it does at least allow a lowest plausible limit to sea-level rise to be estimated. This is found to be 38 cm from 1990 to 2100, as any lower value would require that the rate of sea-level drops despite rising temperatures, an inverse of the pattern observed during the 20th century.


Hydrology Report

F7

F2 Defra flood and coastal defence appraisal guidance


Hydrology Report

F8


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F9


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F10


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F11


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F12


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F13


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F14


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F15