1. HYDROLOGY AND WATER MANAGEMENT Ed Maurer Dept. of Civil and Environmental Engineering Univ. of Washington

2. FUNDAMENTAL QUESTIONS (FROM AN ENGINEERING PERSPECTIVE AT LEAST) How much water is there? How much water is needed? What are the effects of water development?

3. Hydrologic cycle

4. Quantifying Water Supply - 1 USGS Gauge network provides daily measurements Problems: missing data, don’t account for upstream conditions, errors at high flows

5. Long Term Variability Case: The Colorado River 18 years of data (1904-1922) showed 16-18 MAF Long term records: 13.5 MAF and highly variable Source: U.S. Bureau of reclamation.

6. A history of the PDO warm cool warm A history of ENSO 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Pacific Decadal OscillationEl Niño Southern Oscillation

7. Effects of the PDO and ENSO on Columbia River Summer Streamflows Cool Warm

8. Climate Change: Changes to Snow Extent and Naturalized Streamflow at The Dalles Current ~2045 April 1 Snow Extent 20th Century Natural Flows Estimated Range of Natural Flow With 2040’s Warming

9. Depletions and “Natural” Flow Colorado River below Hoover Dam, 1934-1970 Variability and Flow Reduced Average Natural: 20.2 kcfs Average Historic: 13.6 kcfs

10. Determining Natural Flow from Gauge Observations 1.Begin with historic measurements 2.Account for timing changes due to impoundment in reservoirs 3.Add in irrigation diversion 4.Subtract return flows from irrigation 5.Add in evaporation from reservoirs 6.This requires cooperation from historians, agricultural experts, hydrologists, and others.

11. Quantifying Water Supply - 2 Where gauges aren’t available: use models This has advantages such as: Examine effects of past development (logging, roads) Hypothetical case of return to natural (undisturbed) state Evaluate future trends

12. Quantifying Water Supply -- Summary To describe water supply we need to understand: Hydrologic interactions between climate/weather, soil moisture, vegetation, snow, and streamflow Slowly-varying signals in climate Effects of watershed diversions and impoundments

13. Quantifying water needs Domestic, Municipal, Industrial Instream Flow Irrigation

14. Effects of Water Development Long-term effects can be unanticipated Excessive pumping of individual wells locally lowers the water table and creates a cone of depression around the well Subsidence may occur when water is withdrawn from aquifers in unconsolidated materials causing pore spaces to collapse Groundwater pollution may come from single point sources or distributed non-point sources including agricultural fertilizers, landfills, oil wells, mines, septic tanks, road salt and underground

15. Long-Term Pumping Effects Santa Cruz River, Arizona

16. Groundwater pumping near the coast Inland pumping can result in contamination of water wells near the coast with salt water

17. Large-scale water development Multi-use reservoir on Tohono O’odham reservation, Arizona Recreation, fish, wildlife, irrigation, groundwater recharge Won Corps of Engineers distinguished design award, 1974

18. Actual Project Max. possible water height: 75 ft. Peak level, 1974-2000: 15 ft. Only gauged since 1998. Design based on downstream measurements from 1954 Ephemeral flow difficult to measure Seepage is difficult to predict

19. Diversions and Stream Flow Skokomish R. Dams built 1926-30

20. Simple Interaction of Diversions and Downstream Uses Semi-hypothetical example using the S.F. Skokomish

21. System Model More complicated interactions and feedbacks of diversions and benefits. Evaluate consequences of decisions using economic values of uses Source: S. Lansing, U. Arizona.

22. Conclusions An understanding of hydrology is essential for quantifying water supplies and determining water needs. To satisfy water needs (and put water rights to use), priorities of uses must be established (instream/agricultural) Careful study of the interaction of different uses is needed to avoid conflicts Even carefully studied projects can have unanticipated consequences.

23. Timing in Water Requirements Phase shift between crop water (evapotranspiration) and stream flow Water requirement not met by precipitation is fed by diversion If diversion is not available, storage is needed. Reliability determined by variability of flows and size of storage Precip. Evap.. Flow.