Identification of King County Streams with Declining Summer Flows

1. Identification of King County Streams with Declining Summer Flows HydroFutures: Water Science, Technology, and Communities Curtis DeGasperi, curtis.degasperi@kingcounty.gov King County Water and Land Resources Division July 13, 2010

2. Motivation • Wastewater Treatment Division Reclaimed Water Comprehensive Planning Process • What are the potential volumes of reclaimed water that would be needed to serve the potential uses for reclaimed water? http://www.kingcounty.gov/environment/wastewater/ReclaimedWater/CompPlan.aspx

3. Human Impacts on Water Cycle • Land cover change • Forest clearing/Development ~1880

4. “Trends in Qmean and Qmin were not consistent in urban streams and, in fact, trends in these statistics were observed for some suburban and rural streams lacking extensive changes in land use at the scale of a drainage basin over the entire period of record. Although urban development may affect Qmean or Qmin in some streams, relations between development and these statistics were not consistent.” p. 35 - Konrad and Booth (2002) ~1880

5. Human Impacts on Water Cycle Water management • Surface water and groundwater extraction • Consumptive uses (Irrigation) • Septic vs Wastewater conveyance • Pipeline infiltration/exfiltration

6. Water Management Water Supply System Imports Exports Withdrawals Precipitation Basin Water Resources Streamflow Evaporation/ Transpiration I & I Return via septic system disposal Wastewater Disposal Exports

7. Weight-of-Evidence Approach • Review previous studies and reports • Evaluate long term stream flow data for trends

8. Previous Studies/Reports

9. Selected Stream Gauges

10. General Approach • Conduct trend analysis on mean annual and summer (7-day) low flow • Include consideration of trends in precipitation and temperature (Sea-Tac) • Attempt to provide some explanation for observed trends King County. 2009. Working Draft. Identification of Streams Likely to Benefit from Additional Water Inputs. Prepared by Curtis DeGasperi and Jeff Burkey. Water and Land Resources Division, Seattle, WA.

11. Trend Analysis • Non-parametric “distribution free” method • Mann-Kendall Trend test http://pubs.usgs.gov/sir/2005/5275/

12. Trend Analysis • p between 1.0 and 0.1 (weakest evidence) • p between 0.1 and 0.05 (weak evidence) • p between 0.05 and 0.01 (strong evidence) • p <0.01 (strongest evidence)

13. “Nothing is certain, but I think some things are more nearly certain than others” - Bertrand Russell (paraphrased)

14. Trend Analysis

15. Trends in Summer Low Flow

16. Big Soos Creek (example)

17. Precipitation Trends

18. Newaukum Creek (example)

19. Air Temperature Trends

20. Potential influence on ET • Model with temperature trend • Model without temperature trend ?

21. Big Soos Creek (example)

22. Water Conservation

23. Additional Explanation? • To what extent can the effect of land cover change and water management activities be ascribed to these changes? King County. 2009. Working Draft. Preliminary Estimates of Summer Environmental Restoration Flow Targets in Streams Identified as Likely to Benefit from Additional Water Inputs. Prepared by Curtis DeGasperi. Water and Land Resources Division, Seattle, WA.

24. Land Cover Effect • HSPF model unit flow predictions by Hydrologic Response Unit • Forested Till • Disturbed Till • Forested Outwash • Disturbed Outwash • Saturated Soils • Effective Impervious Area

25. Water Management Water Supply System Imports Exports Withdrawals Precipitation Basin Water Resources Streamflow Evaporation/ Transpiration I & I Return via septic system disposal Wastewater Disposal Exports

26. Water Management • Sammamish-Washington Basin • King County (2001) • Green River Basin • Northwest hydraulic consultants (2005) King County. 2001. Screening level analysis of 3rd order and higher WRIA 8 streams for change in hydrologic regime. Draft report prepared by David Hartley for the WRIA 8 Technical Subcommittee on Flow Regime. King County Department of Natural Resources, Water and Land Resources Division: Seattle, WA. Northwest Hydraulic Consultants, Inc. 2005. Assessment of current water quantity conditions in the Green River basin. Prepared for WRIA 9 Steering Committee. Northwest Hydraulic Consultants, Inc., Seattle, WA.

27. Human Influence Big Soos Creek (12112600) July – October 2007

28. Human Influence • Environmental Flow Targets (cfs) - 0.9 to 5 cfs - 5 to 10 cfs -10 to 25 cfs

29. Human Influence • Reduction in natural flow (%) - 14 to 37 % - 38 to 59 % - 60 to 82 %

30. Human Influence • Relative importance of land cover vs water management? • Depends on basin • Highly urbanized basin with external water sources • Suburban basin with local water sources • Modified by type of wastewater disposal system and/or irrigation practices

31. Evidence for Potential Human Influence? Mercer/Kelsey Creek in Bellevue, WA

32. Evidence for Potential Human Influence? Bellevue, WA

33. Conclusions • Well designed long-term gauging network • Compilation and access to up-to-date water management data • Good models to synthesize information and extrapolate to ungauged basins

34. “No amount of sophistication is going to allay the fact that all your knowledge is about the past and all your decisions are about the future” - Ian E. Wilson (former chairman of GE)