1. Hydrological Study of a stream catchment in Palau Pacific HYCOS - www.pacific-hycos.org SOPAC 39 th STAR Session - Nadi 18 th October 2010

2. 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

3. Why is this data needed in Palau ? Pacific HYCOS - www.pacific-hycos.org Box culverts Bridging Water availability for small scale Irrigation & food production

4. Pacific HYCOS - www.pacific-hycos.org Design of water storagesDam safety (PMF), spillway design & dambreak studies (Ngerimel Dam 20 Mill gallons) Water availability and demand – weirs, intakes and treatment plants

5. 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

6. From field data to planning/design Pacific HYCOS - www.pacific-hycos.org

7. Palau’s National Hydrological Archive Pacific HYCOS - www.pacific-hycos.org Only one data file for all of the national data

8. Measurement of continuous water levels Pacific HYCOS - www.pacific-hycos.org Float & weight recorders Bubbler systems & automatic raingauges Gauge boards

9. Rating curve development Pacific HYCOS - www.pacific-hycos.org Medium flows and floods Low flows A provisional curve only, no medium to high flows measured Note extrapolation based on questionable USGS old curve

10. Tabercheding Catchment Pacific HYCOS - www.pacific-hycos.org Catchment area 12.24 km 2 Catchment perimeter 18.88 km Specific min low flow yield April 2010 1.2 litres/km 2 * Specific flood yield July 2009 8.5 m 3 /s per km 2 * * Very limited data available

11. Sample outputs - water level only Pacific HYCOS - www.pacific-hycos.org USGS data HYCOS data

12. Sample outputs – rated (flow) data Pacific Islands Applied Geoscience Commission www.sopac.org Level + rating = flow data, we can use this if the ratings are accurate USGS HYCOS

13. Min and maximum flows Pacific HYCOS - www.pacific-hycos.org A short dataset with no calibrated flow rating cannot be used for flood analysis, however our very provisional rating indicated the maximum flow was 115 m 3 /s, but It could be 150 m3/s or 80 m3/s, what are the implications ?

14. Flow duration/distribution Pacific HYCOS - www.pacific-hycos.org 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 ?

15. Monthly mean flows Pacific HYCOS - www.pacific-hycos.org Note – insufficient data to establish the mean flow, need min of 5 years

16. Daily mean – perhaps Mar/Apr were approaching drought ?? Pacific HYCOS - www.pacific-hycos.org

17. Flow vs daily rainfall – what is the link ? Pacific HYCOS - www.pacific-hycos.org Note – the rain gauge is at the lower end of the catchment If these were floods, might there be a relationship between rainfall & runoff ?

18. Water availability during a dry period in 2010 Pacific HYCOS - www.pacific-hycos.org What have we learnt ? 7 day minimum Q of up to 38/lsec (up to 23,000 m 3 available for 7 days or average of 3,280 m 3 /day) Minimum Q of 15/lsec on 15 th April (1300 m 3 available) Would this compromise reliability of a water demand scheme ? This is based on a 18 month dataset, but it can assist in planning and project design, if we had 10 years of good continuous data ???

19. In closing …. Pacific HYCOS - www.pacific-hycos.org Pacific HYCOS Project is at an end Unless ongoing substantial support is available to NHS’s sustainable data collection activities will remain compromised especially 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”