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FULLTEXT01- Rainfall Runoff Modelling

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    Examensarbete vid Institutionen fr geovetenskaper

    ISSN 1650-6553 Nr 228

    Rainfall-runoff Model Application in

    Ungauged Catchments in Scotland

    Alexander Peter Anthony Fionda

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    I

    Abstract

    Rainfall-runoff model application for ungauged catchments in Scotland

    Alexander Peter Anthony FiondaDepartment of Earth Sciences, Uppsala University

    Villavgen 16, SE-752 36 Uppsala, Sweden.

    The conceptual rainfall-runoff model Hysim is used to estimate the flow in ungauged

    catchments in Scotland by Scottish Water. However, there are non-quantified uncertainties

    associated with the outcomes of the modelling strategy used. In order to identify and quantify

    these uncertainties it was necessary to use the framework of proxy-basin validation in order

    to evaluate the performance of different modelling strategies.

    The proxy-basin validation test requires hydrologically analogous catchments for the

    evaluation of models, a Region Of Influence regionalisation method was used in order group

    selected catchments by Q95(%MF). Four groups of four catchments were established, which

    covered Q95(%MF) 5-7%, 7-9%, 9-11% and 11-13%.

    The allocation of donor catchment and target catchment for each Q95(%MF) group

    was accomplished through discussion with Scottish Water with respect to existing Scottish

    Water modelled catchments. A single donor catchment and three target catchments were

    therefore indicated for each group.

    Two modelling strategies were developed by the study; the first full transposition method

    used the entire optimised parameter-set from the donor catchment with the exception of the

    target catchments catchment area parameter. The second partial transposition method usedthe entire optimal parameter-set with the exception of the target catchments interception

    storage, time to peak, rooting depth and catchment area parameters.

    It was found that the full transposition method had the least uncertainty associated its use

    for flow estimation when the parameter-set was derived from a donor catchment calibration

    that was excellent. Contrarily, it was found that the partial transposition model method had

    the least uncertainty associated with flow estimation for parameter-sets that were derived

    from a relatively poor donor catchment calibration.

    Encouraged by this testing framework, this study has suggested the use of catalogue of

    donor parameter-sets that can be used to estimate flow for catchments that are hydrologicallysimilar. This strategy of hydrological modelling has been recommended to improve existing

    Scottish Water Hysim methodology.

    Keywords

    ungauged catchment, proxy-basin validation, region of interest, transposition method, hysim,

    rainfall-runoff model, sepa, scottish water, scotland.

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    II

    Referat

    Anvndning av en avrinningsmodell i ett skotskt avrinningsomrde utan

    vattenfringsmtningar

    Alexander Peter Anthony Fionda

    Institutionen fr geovetenskaper, Uppsala universitet

    Villavgen 16, 752 36 UPPSALA.

    Scottish Water anvnder den begreppsmssiga avrinningsmodellen Hysim fr att uppskatta

    vattenfringen i skotska avrinningsomrden utan vattenfringsdata. Den valda

    modelleringsstrategin har emellertid resulterat i icke-kvantifierade oskerheter i berknade

    vattenfringar. Fr att identifiera och kvantifiera de oskerheter som r frbundna med olika

    modelleringsstrategier var det ndvndigt att anvnda sig av information frn likartadeavrinningsomrden.

    Den valda regionaliseringsmetoden anvnde hydrologiskt analoga avrinningsomrden som

    definition p likhet. Analogin grundades p inflytanderegion (Region of Influence) som

    erhlls genom att gruppera utvalda avrinningsomrden utefter Q95 (% medelflde). Fyra

    grupper med fyra avrinningsomrden valdes ut grundat p fljande Q95-grnser (%

    medelflde): 5-7%, 7-9%, 9-11% and 11-13%.

    Frdelningen av analoga avrinningsomrden (omrden med vattenfringsmtningar vars

    parametervrdesuppsttningar skulle verflyttas) och mlomrden (utan mtningar) fr varje

    Q95-grupp erhlls efter diskussion med Scottish Water frn omrden dr Scottish Water

    modellerat vattenfringen. Ett analogt omrde och tre mlomrden valdes ut fr varje grupp.

    Studien anvnde tv modelleringsstrategier. Den frsta metoden, total verflyttning,

    anvnde hela parametervrdesuppsttningen frn det analoga omrdet med undantag av

    mlomrdets area. Den andra metoden, partiell verflyttning, anvnde hela

    parametervrdesuppsttningen med undantag fr mlomrdets interceptionslager, tid till

    hgflde, rotdjup och area.

    Den totala verflyttningsmetoden hade lgst oskerhet nr parametervrdesuppsttningen

    hrleddes frn ett omrde med utmrkt kalibrering. Den partiella verflyttningsmetoden hade,

    andra sidan, lgst oskerhet nr parametervrdesuppsttningen hrleddes frn ett omrde

    med dlig kalibrering.

    Efter att ha provat de tv metoderna utmynnade studien i ett frslag till en katalog med

    parametervrdesuppsttningar fr omrden som kan bedmas som hydrologiskt lika. Denna

    strategi fr hydrologisk modellering har rekommenderats som frbttring av befintlig Hysim-

    metodik hos Scottish Water.

    Nyckelord

    Avrinningsomrde utan vattenfringsdata, validering mot likartade omrden,

    inflytanderegion, verflyttningsmetod, hysim, avrinningsmodell, SEPA, Scottish Water,

    Skottland.

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    III

    Contents

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

    1.1 Research objectives ................................................................................................. 1

    1.1.2 Scottish Water and its resource systems .......................................................... 2

    1.1.2 The role of hydrologic modelling in Scottish Water ........................................ 5

    1.2 The use of Hysim rainfall-runoff modelling by Scottish Water............................ 12

    1.2.1 Quantifying the uncertainty associated with parameterisation ...................... 13

    1.2.2 Modelling flow in ungauged catchments ....................................................... 15

    1.3 Key questions and summary of methods ............................................................... 16

    2 Materials and Methods................................................................................................. 18

    2.1 Analogue and target site selection from SEPA catchments .................................. 18

    2.2 The Hysim conceptual rainfall-runoff model ........................................................ 21

    2.3 Derivation of inputs ............................................................................................... 24

    2.4 Hysim model calibration ....................................................................................... 26

    2.5 Development of parameter transposition methods ................................................ 27

    2.6 Evaluating model performance using the proxy-basin test ................................... 28

    3 Results.......................................................................................................................... 29

    3.1 Hydrological statistics of mega-zones and SEPA catchments .............................. 29

    3.2 Calibration quality of donor catchments ............................................................... 31

    3.3 Evaluating model performance with transposition method chosen....................... 39

    3.4 Evaluating model performance with selection of target catchment ...................... 44

    4 Discussion .................................................................................................................... 47

    4.1 Hydrological statistics of mega-zones and SEPA catchments .............................. 474.2 Calibration quality of donor catchments ............................................................... 48

    4.3 Uncertainty identified with selection of target catchment..................................... 53

    4.4 A more pragmatic methodology for estimations of flow ...................................... 54

    5 Conclusion ................................................................................................................... 56

    6 Acknowledgements...................................................................................................... 58

    7 References.................................................................................................................... 59

    8 Appendices................................................................................................................... 63

    Appendix A: Hysim operational notes ........................................................................... 63

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    IV

    Appendix B: Parameter-set references ........................................................................... 64

    Appendix C: Results of validation ................................................................................. 65

    Definition of terms

    MF - the mean flow.

    Q95 - the 95th

    percentile of mean flow; the flow exceeded or equalled 95 % of the time.

    Q95(%MF) - the

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