Hydrological Study of a stream catchment in Palau Pacific HYCOS - SOPAC 39 th STAR Session - Nadi...

Hydrological Study of a stream catchment in Palau

Pacific HYCOS - www.pacific-hycos.org

SOPAC 39th STAR Session - Nadi 18th October 2010

Presentation Outline


•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 ?


Box culverts Bridging

Water availability for small scale Irrigation & food production


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


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


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


Only one data file for all of the national data

Measurement of continuous water levels


Float & weight recorders

Bubbler systems

& automatic raingauges

Gauge boards

Rating curve development


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ge m

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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


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


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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

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Flo

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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

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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


~~~ 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


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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


~~~ 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 ??


Flow vs daily rainfall – what is the link ?


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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

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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


~~~ 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 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”

Hydrological Study of a stream catchment in Palau Pacific HYCOS - SOPAC 39 th STAR Session - Nadi...

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