Yantao Cui 1 , Christian Braudrick 1,2 , and Steve Rothert 3

1. 2005 EWRI Conference, Williamsburg, July 19-22, 2005 A Preliminary Evaluation of the Potential Downstream Sediment Deposition Following the Removal of Four Dams on the Klamath River Yantao Cui1, Christian Braudrick1,2, and Steve Rothert3 • Stillwater Sciences, 2855 Telegraph Ave., Suite, Berkeley, CA 94705 • Now at Department of Earth and Planetary Sciences, UC Berkeley • American Rivers, 409 Spring Street, Nevada City, CA 95959

2. Objective of this Presentation • For those who are interested in dam removal projects in general, we will introduce the dams on the Klamath River and our preliminary study results; • For those who are interested in conducting dam removal sediment transport analysis, we are hoping to demonstrate how limited resources and information may be used to produce certain useful results.

3. Copco 2 Oregon California Sketch modified from Eilers and Gubala (2003)

4. Eilers and Gubala (2003) Copco 2

5. Irongate Dam on the Klamath River, California -- Photo taken by Y. Cui 5

6. Eilers and Gubala (2003) 6

7. Eilers and Gubala (2003)

8. Sediment in the Reservoirs (in yd3) (Based on Eilers and Gubala 2003) 15,200,000 * Copco 2 has only about 8,000 cubic yard of sediment deposit.

9. Initial Study Objectives • Here is $20,000! How can we spend it wisely to get some understanding of the potential consequences following the removal of the four dams?

10. Based on Ayres Associate (1999) Based on Ayres Associate (1999) Measured from aerial photograph

11. Sediment deposit in Copco delta area Photo taken by Y. Cui 11

12. PacifiCorp (2003) 12

15. Based on existing information and a reconnaissance level field trip, we believed that downstream sediment deposition following dam removal would be minimal. • Based on this initial professional judgment, we developed the rest of the study objectives:

16. Redefined Study Objectives • to conduct preliminary simulation under an assumed worst-case-scenario to confirm our initial professional judgment that there will be minimal sediment deposition downstream of the dams; • and from which, to have a preliminary understanding of the potential increase in flooding risks following dam removal.

17. To conduct the analysis withDREAM-1 • DREAM-1 is one of the two Dam Removal Express Assessment Models developed at Stillwater Sciences, Berkeley, California. • DREAM-1 simulates sediment transport following dam removal in which reservoir sediment is composed primarily of non-cohesive fine sediment. • Details of the Dam Removal Express Assessment Models can be found in two upcoming Journal of Hydraulic Research papers.

18. Worst-Case-Scenario for downstream sediment deposition • Assume a larger volume of sediment release; • Assume a higher fraction of coarser sediment in the deposit; • Assume no impact from cohesiveness, and thus, allowing for quicker sediment erosion; • Assume sediment is distributed closer to the dam, thus reducing the potential attenuation effect provided by the extra river length in the reservoir; • Assume the dam will be removed instantly after a 6-month drawdown; • Simulate both dry and wet water years to envelope potential hydrologic conditions.

19. Removal Assumptions • Removing J.C. Boyle and the two Copco dams before the final removal of Irongate Dam. • A portion of the sediment from J.C. Boyle and the two Copco dams will be eroded, transported and deposited in the Irongate Reservoir. The amount of sediment from the upstream reservoirs deposited into the Irongate Reservoir is assumed according to the sprit of “worst-case-scenario” assumption. • A diversion tunnel left behind from dam construction will be used to draw the Irongate Reservoir down uncontrolled, and will allow for a 6-month period to remove the upper potion of the dam. At that point the entire dam will be removed.

20. Simulating a dry and a wet water year • A wet year will evacuate reservoir sediment faster, and as a result, may result in higher downstream sediment deposition; • A dry year will evacuate reservoir sediment more slowly but its downstream sediment transport capacity is also lower. This may also result in a higher downstream sediment deposition.

21. 21 Reservoir Drawdown Period,Dry Water Year

22. 22 Reservoir Drawdown Period,Dry Water Year

23. After the Entire Dam is Removed,Dry Water Year

24. 24 After the Entire Dam is Removed,Dry Water Year

25. Conclusions • We were able to conduct a “worst-case-scenario” analysis with regard to downstream sediment deposition following the removal of the four dams on the Klamath River with very limited information and resources. • Preliminary results indicate that, under the worst-case-scenario assumptions, downstream sediment deposition is limited to within about 8 miles downstream of Irongate Dam with a maximum deposition thickness of about 4 ft, which lasts for about 6 months. We anticipate a much thinner sediment deposit following dam removal, which will last much shorter than predicted with the worst-case-scenario assumptions.

26. Conclusions - continued • Increased flooding risks associated with aggradation is relatively low, given the limited amount of sediment deposition predicted under the worst-case-scenario, and the fact that during a really high flow event most sediment will be suspended, and sediment will be eroded especially quickly out of the concerned reach. • The key factor that will determine the strategy in removing the four dams on the Klamath River will be the high suspended sediment concentration and turbidity level, which cannot be simulated without further data collection.

27. Acknowledgment • Funding for this study was provided jointly by American Rivers, Trout Unlimited, California Trout, Friends of the River, and Stillwater Sciences. • Suggestions, helps, and critiques from Brian Cluer, Bill Dietrich, Dennis Gathard, Gordon Grant, Frank Ligon, Tom Lisle, Tim Randle, and Laura Wildman are gratefully acknowledged.