Optimized Flood Control in the Columbia River Basin for a Global Warming Scenario

1. Optimized Flood Control in the Columbia River Basin for a Global Warming Scenario Se-Yeun Lee1, Alan F. Hamlet 2,1 Carolyn J. Fitzgerald3 Stephen J. Burges1 Dennis P. Lettenmaier1, 2 Dept. of Civil and Env. Engineering, UW CSES Climate Impacts Group, UW U.S. Army Corps of Engineers, Seattle District

2. Motivation

3. Red - Negative Trend Blue – Positive Trend Trends in April 1 Snowpack from 1950-1997 Mote P.W.,Hamlet A.F., Clark M.P., Lettenmaier D.P., 2005, Declining mountain snowpack in western North America, BAMS, 86 (1): 39-49

4. As the West warms, spring flows rise and summer flows drop Stewart IT, Cayan DR, Dettinger MD, 2005: Changes toward earlier streamflow timing across western North America, J. Climate, 18 (8): 1136-1155 Red - Negative Trend Blue – Positive Trend

5. Hydrologic Impacts of Global Warming on Snowmelt Dominant Rivers • Increased Winter Flows • Reduced Spring Snowpack • Earlier Melt • Earlier Spring Peak Flow • Decreased Summer Flow

6. Flood Control vs. Refill : Current Climate Full

7. Flood Control vs. Refill : Current Climate : + 2.25 oC No adaption Streamflow timing shifts can reduce the reliability of reservoir refill + 2.25 oC Full

8. Flood Control vs. Refill : Current Climate : + 2.25 oC No adaption : + 2.25 oC plus adaption Streamflow timing shifts can reduce the reliability of reservoir refill + 2.25 oC Full

9. Refill Flood Control Objective: • Develop Systems Engineering Procedures for Rebalancing Flood Control and Reservoir Refill

10. Test Case: The Columbia River Basin Multi-objective Reservoir System • Flood Control • Hydropower • Instream Flow • Water Supply • Recreation • Navigation

11. Bonners Ferry Columbia Falls The Dalles Major U.S. Flood Control Checkpoints

12. Optimization –Simulation Models Methods • Developing Optimized Flood Control Curves • Testing and refining Proposed Rule Curves

13. HEC-PRM (Hydrologic Engineering Center’s Prescriptive Model) • Optimization model developed by the US Army Corps of Engineers • Penalty functions are used to constrain the Columbia River basin system operation • Flood control penalties • Storage penalties

14. ColSim (Columbia Simulation Model) • Flood control • Hydropower • Irrigation • Instream flow • Navigation • Recreation

15. Adjust Parameters Calibration Strategy

16. Calibration Results

17. Calibration Results (Refill)

18. Columbia Falls Bonners Ferry The Dalles Calibration Results (Flood Control) Red - Current FC Blue - Optimized FC

19. VIC Hydrologic Model (Variable Infiltration Capacity Hydrologic Model) • Macroscale Hydrologic Model developed by University of Washington

20. Climate Change Scenario • Remove historic monthly temperature trends from the daily time step forcing data • Increase the temperatures by 2 oC (annual average) in a seasonal pattern derived from several GCM simulations • Observed precipitation

21. : Current Climate : Climate Change Scenario Monthly Simulated Reservoir Inflows

22. Creating New Flood Control Rule Curves

23. Current Flood Rule Curves • Flood Control Rule Curves are selected by Apr-Jul Flow Volume

24. New Flood Rule Curves • Find Flow Volume Ranges for each category with an equal number of events

25. FC 4 New Flood Rule Curves • Find Flow Volume Ranges for each category with an equal number of events • Use 80thpercentile values for each categories as a Flood Rule Curve : 17 ensemble traces : 80th percentile of ensembles

26. Optimization Model ResultsCurrent Climate vs Climate Change Scenario

27. Feb Mar Dworshak storage(Dworshak Apr-Jul flow volume >2.40 MAF) a) 20th Century Climate b) Climate Change Scenario : Ensemble traces : 80th percentile of ensembles

28. Mar Apr Libby storage (Libby Apr-Aug flow volume >5.5 MAF) a) 20th Century Climate b) Climate Change Scenario : Ensemble traces : 80th percentile of ensembles • The changes in flood control rule curves are different for different projects

29. Simulation Model Results:Reservoir Storage Results

30. Full Refill Probability of Libby (Libby Apr-Aug flow volume>5.5 MAF)

31. Refill Probability of Dworshak (Dworshak Apr-Jul flow volume >2.40 MAF)

32. : The Dalles Apr-Aug < 68 MAF : 68 <= The Dalles Apr-Aug <100 MAF : The Dalles Apr-Aug >=100 MAF • Greatest Improvement occurs in Mid flow years ( ) Changes in Reservoir Storage

33. Simulation Model Results:Flood-Frequency Results

34. Flood-Frequency Curves for Bonners Ferry

35. Flood-Frequency Curves for Columbia Falls

36. Flood-Frequency Curves for The Dalles

37. Conclusions • Optimization studies provide an objective method for rebalancing flood control and refill objectives in complex reservoir systems in response to hydrologic changes. • The changes in flood control rule curves are different for different projects, corresponding to different changes in flow volume and timing associated with warming in each sub basin.

38. Conclusions • Optimized flood control rule curves show reduced flood evacuation and earlier refill timing; up to one month earlier for a climate change scenario, compared with 20th century climate. • For the climate change scenario, optimized flood rule curves increase reservoir refill as well as the system storage in moderate and high flow years, while providing comparable levels of local and system-wide flood protection in comparison to the current flood control rule curves.

39. Future Work • Extension and refinement of our methods using daily time step optimization and simulation models is needed to evaluate the robustness of these techniques in more detailed planning studies.

40. Questions?