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Hydrological Study of a stream catchment in Palau

Hydrological Study of a stream catchment in Palau. SOPAC 39 th STAR Session - Nadi 18 th October 2010. Pacific HYCOS - www.pacific-hycos.org. Presentation Outline. Hydrological study on a large catchment in Palau, Island of Babeldaob Why is such a study necessary How is this undertaken

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Hydrological Study of a stream catchment in Palau

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

  2. 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 Pacific HYCOS - www.pacific-hycos.org

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

  4. 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

  5. Catchment health, water safety planning In stream flow requirements, base flow assessment Tourism opportunities Ridge to reef considerations, eg GBRMPA Pacific HYCOS - www.pacific-hycos.org

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

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

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

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

  10. 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 2009 8.5 m3/s per km2 * * Very limited data available Pacific HYCOS - www.pacific-hycos.org

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

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

  13. Min and maximum flows 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 m3/s, but It could be 150 m3/s or 80 m3/s, what are the implications ? Pacific HYCOS - www.pacific-hycos.org

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

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

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

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

  18. Water availability during a dry period in 2010 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 planning and project design, if we had 10 years of good continuous data ??? Pacific HYCOS - www.pacific-hycos.org

  19. In closing …. • 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” Pacific HYCOS - www.pacific-hycos.org

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