Hydrological Study of a stream catchment in Palau Pacific HYCOS - SOPAC 39 th STAR Session - Nadi 18 th October 2010.
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Hydrological Study of a stream catchment in Palau
Pacific HYCOS - www.pacific-hycos.org
SOPAC 39th STAR Session - Nadi 18th October 2010
Presentation Outline
Pacific HYCOS - www.pacific-hycos.org
•Hydrological study on a large catchment in Palau, Island of Babeldaob
•Why is such a study necessary
•How is this undertaken
•What is required
•What are the outputs
Why is this data needed in Palau ?
Pacific HYCOS - www.pacific-hycos.org
Box culverts Bridging
Water availability for small scale Irrigation & food production
Pacific HYCOS - www.pacific-hycos.org
Design of water storages Dam safety (PMF), spillway design & dambreak studies (Ngerimel Dam 20 Mill gallons)
Water availability and demand – weirs, intakes and treatment plants
Pacific HYCOS - www.pacific-hycos.org
Catchment health, water safety planning In stream flow requirements, base flow assessment
Ridge to reef considerations, eg GBRMPA Tourism opportunities
From field data to planning/design
Pacific HYCOS - www.pacific-hycos.org
Typical outputs by NHS
daily or monthly mean flows
maximum and minimum flows
flow durations
statistical anlaysis
identify drought sequences
various graphic and tabular outputs
flood analysis
Note without a regular field program implemented toundertake essential discharge measurements, we cannot get streamflow data and we cannot assess the water resource, floods, droughts or climatic varability
National Hydrological Service
Hydrological data collection program;
. Rainfall. Stream level/flow
. Groundwater. Water quality
. Sediment. climatic
NationalHydrologicalArchive
(TIDEDA)
long term consistent calibrated datasets available for data analysis and modelling
various models for rainfall runoff, flood estimation, hydraulic and flood plain models, dambreak, integrated catchment estuary modelling, groundwater analysis
Water level data(15 minute)
Stream flow measurements(physical)
develop stream flow rating curves
Combine WL and ratings to get dischargein TIDEDA, we now have data we can useespecially if long term quality data !
Quality control,
assurance and audits
Typically undertaken
by consultants
Palau’s National Hydrological Archive
Pacific HYCOS - www.pacific-hycos.org
Only one data file for all of the national data
Measurement of continuous water levels
Pacific HYCOS - www.pacific-hycos.org
Float & weight recorders
Bubbler systems
& automatic raingauges
Gauge boards
Rating curve development
Pacific HYCOS - www.pacific-hycos.org
0
1000
2000
3000
4000
5000
Sta
ge m
m
0 10 20 30 40 50 60 70 80 90 100Flow m3/s
Site 16890850 Tabecheding R at Above Compact Rd Gaugings from 1-Jan-2009 to 21-Jul-2009 1-Jan-2009 12:00:00 Indicator Stage 1237
Medium flows and floods
Low flows
A provisional curve only, no medium to high flows measured
Note extrapolation based on questionable USGS old curve
Tabercheding Catchment
Pacific HYCOS - www.pacific-hycos.org
Catchment area 12.24 km2
Catchment perimeter 18.88 km
Specific min low flow yield April 2010 1.2 litres/km2 *
Specific flood yield July 20098.5 m3/s per km2 *
* Very limited data available
Sample outputs - water level only
Pacific HYCOS - www.pacific-hycos.org
0
1000
2000
3000
4000
5000
6000
7000
8000
8450
Sta
ge m
m
24-Jun-2002 15:00 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10site 16890850 Tabecheding R at Above Compact Rd Stage mm
USGS data
HYCOS data
Sample outputs – rated (flow) data
Pacific Islands Applied Geoscience Commission www.sopac.org
0
50
120
Flo
w m
3/s
Jan-2002 Apr-02 Jul-02 Oct-02 Jan-03 Apr-03 Jul-03 Oct-03site 16890850 Tabecheding R at Above Compact Rd Flow m3/s
0
50
120
Flo
w m
3/s
Jan-2009 Apr-09 Jul-09 Oct-09 Jan-10 Apr-10 Jul-10 Oct-10site 16890850 Tabecheding R at Above Compact Rd Flow m3/s
Level + rating = flow data, we can use this if the ratings are accurate
USGS
HYCOS
Min and maximum flows
Pacific HYCOS - www.pacific-hycos.org
~~~ NIWA Tideda ~~~ SOPAC 15-OCT-2010 13:24 ~~~ PEXTREME ~~~ Source is Palau Archive.MTD Site 16890850 Tabecheding R at Above Compact Rd From 1-Jan-2002 15:00:00 to 1-Jan-2011 10:00:00 Interval = 0 Flow m3/s Coeff. Year Mean of Var. Minimum Date Maximum Date ---- ---- ------- ------- ---- ------- ---- *2002 1.2765 2.73 7.60000E-02 11-Sep-2002 24:00 55.757 22-Dec-2002 10:15 *2003 1.9936 2.28 8.70000E-02 22-Apr-2003 24:00 114.98 11-Jun-2003 13:45 *2004 0.94780 1.03 0.24600 20-Apr-2004 22:30 11.713 16-Mar-2004 05:00 2005 No values for this year 2006 No values for this year 2007 No values for this year 2008 No values for this year *2009 1.5256 2.90 0.13900 20-Mar-2009 22:40 105.52 28-Jul-2009 05:40 *2010 0.94319 2.41 -2.00000E-03 1-Apr-2010 00:20 49.321 14-Jan-2010 21:40 '*' denotes years with gaps in the data or incomplete years Coeff. of Var. = sd/mean Minimum is -2.000000E-03 at 1-Apr-2010 00:20:00 Maximum is 114.982 at 11-Jun-2003 13:45:00 Mean is 1.43957 Std. Dev. is 3.79130 Coeff. of Var. is 2.63 End of process
A short dataset with no calibrated flow rating cannotbe used for flood analysis, however our very provisional
rating indicated the maximum flow was 115 m3/s, but It could be 150 m3/s or 80 m3/s, what are the implications ?
Flow duration/distribution
Pacific HYCOS - www.pacific-hycos.org
-10
0
20
40
60
80
100
120
Flo
w m
3/s
0 10 20 30 40 50 60 70 80 90 100Percentage of time flow is equalled or exceeded
site 16890850 Tabecheding R at Above Compact Rd Flow m3/s 24-Jun-2002 15:00:00 to 1-Jan-2011 10:00:00
Mean flow
Important for engineers, designers and planners,how much water is available and how long is it there,especially for low flow analysis
What % of time can a particular demand be supplied,Eg we may be required to meet a 95% reliability factor,whereas measured data may indicate that only 70% can be met
What do we do, reduce the demand ? alternative water ?
Monthly mean flows
Pacific HYCOS - www.pacific-hycos.org
~~~ PCAL ~~~ Source is C:\HYCOS\Pacific TIDEDA Data\Palau\Palau Archive\Palau Archive.MTD Monthly means 2002 to 2010 site 16890850 Tabecheding R at Above Compact Rd Flow m3/s Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean 2002 ? ? ? ? ? ? 1.264 1.031 0.358 0.921 ? 0.848 0.888? 2003 0.990 1.755 0.874 0.385 4.185 3.058 2.283 0.980 3.687 ? ? ? 2.021? 2004 ? ? ? ? ? ? ? ? ? ? ? ? ? 2005 ? ? ? ? ? ? ? ? ? ? ? ? ? 2006 ? ? ? ? ? ? ? ? ? ? ? ? ? 2007 ? ? ? ? ? ? ? ? ? ? ? ? ? 2008 ? ? ? ? ? ? ? ? ? ? ? ? ? 2009 ? ? 0.459 1.614 0.723 1.737 4.719 0.914 1.509 0.775 1.937 0.954 1.532? 2010 1.283 0.396 0.127 0.358 0.496 1.023 1.604 2.349 ? ? ? ? 0.963? Min. 0.990 0.396 0.127 0.358 0.496 1.023 1.264 0.914 0.358 0.775 1.937 0.848 ? Mean 1.137 1.075 0.486 0.786 1.801 1.939 2.467 1.318 1.851 0.848 1.937 0.901 ? Max. 1.283 1.755 0.874 1.614 4.185 3.058 4.719 2.349 3.687 0.921 1.937 0.954 ? The Min Mean and Max of Annual means are for complete years only. End of process
Note – insufficient data to establish the mean flow, need min of 5 years
Daily mean – perhaps Mar/Apr were approaching drought ??
Pacific HYCOS - www.pacific-hycos.org
Flow vs daily rainfall – what is the link ?
Pacific HYCOS - www.pacific-hycos.org
0
0.5
1
1.5
2
2.5
3
3.5
4
Flo
w m
3/s
1-Feb-2010 12:00 21-Feb 3-Mar 13-Mar 23-Mar 2-Aprsite 16890850 Tabecheding R at Above Compact Rd Flow m3/s
0
12.5
25
37.5
50
62.5
75
87.5
100
Note – the rain gauge is at the lower end of the catchment
If these were floods, might there be a relationship between rainfall & runoff ?
Water availability during a dry period in 2010
Pacific HYCOS - www.pacific-hycos.org
~~~ NIWA Tideda ~~~ SOPAC 15-OCT-2010 13:47 ~~~ PMOVE ~~~ Source is Palau Archive.MTD Site 16890850 Tabecheding R at Above Compact Rd From 1-Feb-2010 12:00:00 to 10-Apr-2010 12:00:00 Minimum moving averages over 7.000days interval (Non-Overlapping) The 4 smallest values are: (Flow m3/s) 1: 0.038 at interval beginning 27-Mar-2010 20:50:00 2: 0.059 at interval beginning 4-Mar-2010 17:10:00 3: 0.076 at interval beginning 19-Mar-2010 14:40:00 4: 0.326 at interval beginning 6-Feb-2010 11:20:00 End of process
What have we learnt ?
7 day minimum Q of up to 38/lsec (up to 23,000 m3 available for 7 days or average of 3,280 m3 /day)
Minimum Q of 15/lsec on 15th April (1300 m3 available)
Would this compromise reliability of a water demand scheme ?
This is based on a 18 month dataset, but it can assist in planningand project design, if we had 10 years of good continuous data ???
In closing ….
Pacific HYCOS - www.pacific-hycos.org
Pacific HYCOS Project is at an end
Unless ongoing substantial support is available to NHS’ssustainable data collection activities will remain compromisedespecially for datasets to verify and mitigate the effects of:
•Climate change•Flood risk – DRM
Plus
•Infrastructure design•Water resource planning and management•A range of water related projects
“You cant manage what you don’t measure”
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