FORECAST-BASED OPERATIONS AT FOLSOM DAM AND LAKE

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FORECAST-BASED OPERATIONS AT FOLSOM DAM AND LAKE 255 237 237 237 217 217 217 200 200 200 0 163 131 Bridging the Gap163Conference 255 0 132 255 0 163 122 The

1 FORECAST-BASED OPERATIONS AT FOLSOM DAM AND LAKE Bridging the Gap163Conference The Dana on Mission Bay San Diego, CA January 28, Joe Forbis, P.E. Chief, Water Management Section Sacramento District, U.S. Army Corps of Engineers The views, opinions and findings contained in this report are those of the authors(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other official documentation

2 AGENDA Background of American River watershed and Folsom Dam Need for Joint Federal Project (JFP) New forecast-based operations at Folsom Dam

3 AMERICAN RIVER HYDROLOGY Steep watershed Rain-on-snow potential Winter snowpack

4 WATER SUPPLY SYSTEM CONTEXT Central Valley Project US Bureau of Reclamation State Water Project CA Department of Water Resources

5 FOLSOM DAM Folsom Lake Gross Pool (100% full): 967,000 ac-ft Flood Control Space: up to 600,000 ac-ft Avg. Annual Unregulated Runoff: 2,788,000 ac-ft Folsom Dam Main spillway with eight radial gates Elevation ~420 ft; Max release capacity ~567,000 cfs River outlets Max release capacity ~28,000 cfs Auxiliary spillway (JFP) Elevation ~370 ft; Max release capacity ~314,000 cfs

6 FOLSOM DAM FLOOD HISTORY 1944 Folsom Dam authorized Designed to provide 500year level of flood protection 1951 Record Flood 1956 Record Flood 1964 Record Flood New level of protection is 120-year 1986 Record Flood New level of protection is 60-year 1997 Record Flood

7 350,000 NEED FOR JFP 5 300,000 Peak Annual Inflow (Unimpaired) , ,000 Flow (cfs) 150, ,000 50,000 0 Year Construction of Original Dam Complete

8 NEED FOR JFP Problems with the existing dam: Only 400,000 acre-feet of authorized flood storage (wasn t sized to include largest storms) Can t pass the Probable Maximum Flood without overtopping 30% of flood storage used when downstream objective release (115,000 cfs) can be achieved Proposed solutions: Additional upstream flood storage Expansion of existing outlets Auxiliary spillway, additional 200,000 ac-ft of variable flood storage, and forecast-based operations potential

9 EXISTING AND JFP OUTLETS Flood space (KAF) Main Dam JFP Remaining Total Top of flood pool 115K cfs without JFP 115K cfs with JFP Main Dam stilling basin floor

10 HISTORY OF FOLSOM OPERATIONS

11 FORECAST-BASED OPERATIONS Theory: foreknowledge of runoff volume and timing enables optimal use of storage and release decisions Concerns: forecast uncertainty generates risk Insufficient releases (increased flood risk) Excessive releases (water supply risk) Challenges: Limited forecast data record Never been done before

12 TWO BASELINES/THREE ALTERNATIVES Flood Space (TAF) 1,000 0 Existing (USACE) 400 TAF Flood Space Basin Wetness 800 Existing (BOR-SAFCA) 400/670 TAF Flood Space Upstream Storage Credit Storage (TAF) Alternative /600 TAF Flood Space Upstream Storage Credit 400 Alternative 2 400/600 TAF Flood Space Upstream Storage Credit + Basin Wetness Alternative /600 TAF Flood Space Forecasted Inflow Volume 200 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

13 1986 event pattern scaled to 200-yr Forecast operation reflects perfect forecast Existing (BOR/SAFCA) JFP + US credit JFP + Forecast-based

14 NEW FOLSOM WCD

15 NEW FOLSOM WCD

16 FORECAST ENSEMBLE 12/22 59 ensemble traces

17 FORECAST ENSEMBLE 12/23

18 FORECAST ENSEMBLE 12/24

19 FORECAST ENSEMBLE 12/25

20 FORECAST ENSEMBLE 12/26

21 FORECAST ENSEMBLE 12/27

22 FORECAST ENSEMBLE 12/28

23 FORECAST ENSEMBLE 12/29

24 FORECAST ENSEMBLE 12/30

25 FORECAST ENSEMBLE 12/31

26 FORECAST ENSEMBLE 1/01

27 FORECAST ENSEMBLE 1/02

28 FORECAST ENSEMBLE 1/03

29 FORECAST INFLOW VOLUMES 3-day volume updated daily 59 ensemble traces 21 probabilistic traces Each trace reflects one value of NonExceedance Probability (NEP)

30 ROBUSTNESS TESTING Identify smallest NEP that routes design event at target release. Identify greatest NEP that routes design event without drawing down reservoir to bottom of variable space. Identify smallest NEP that routes design event given 24hour time shift in forecasted inflow volumes. Identify greatest NEP value that does not result in drawdowns that do not refill (false positives).

31 ROBUSTNESS 1/200 EVENT (1997)

32 ROBUSTNESS 1/200 EVENT (1997)

33 ROBUSTNESS RESULTS Flood Performance Metric Event, Target Release Minimum Successful NEP 1/ pattern, 115 kcfs 0% (ALL PASS) 1/ pattern, 115 kcfs 0% (ALL PASS) 1/ pattern, 160 kcfs 0% (ALL PASS) 1/ pattern, 160 kcfs 0% (ALL PASS) Drawdown Metric Minimum storage > 367 TAF Maximum Successful NEP 1/ pattern 60% 1/ pattern 80% 1/ pattern 70% 1/ pattern 85%

34 QUESTIONS?

Integrating Weather Forecasts into Folsom Reservoir Operations

Integrating Weather Forecasts into Folsom Reservoir Operations California Extreme Precipitation Symposium September 6, 2016 Brad Moore, PE US Army Corps of Engineers Biography Brad Moore is a Lead Civil