Integrating Weather Forecasts into Folsom Reservoir Operations

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Silas Lloyd
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1 Integrating Weather Forecasts into Folsom Reservoir Operations California Extreme Precipitation Symposium September 6, 2016 Brad Moore, PE US Army Corps of Engineers

2 Biography Brad Moore is a Lead Civil Engineer at the Sacramento District of the U.S. Army Corps of Engineers. He works in the Hydrology and Hydraulics Branch and is the Engineering Technical Lead for the Folsom Dam Water Control Manual Update. In addition to 10 years with the Sacramento District, he has 8 years experience in flood risk management in the Sacramento private sector. He holds a B.S. in Mechanical Engineering, M.S. in Hydrologic Science, and Civil P.E. license. 2

3 Abstract Completion of the Joint Federal Project spillway at Folsom Dam requires the U.S. Army Corps of Engineers to update the Folsom Water Control Manual. The manual defines the maximum allowable storage before flood releases are required and required flood releases when the allowable storage is exceeded. This presentation will describe the tentatively selected flood operation, which relies on inflow forecasts provided by the California Nevada River Forecast Center. The presentation will compare the operation to other alternatives, describe how forecast information is processed and used, and describe testing to account for forecast uncertainty. 3

4 American River Basin 2

5 Folsom Lake and Dam 967 TAF storage (gross pool). Objective flood release is 115 kcfs. Channel capacity ~ 160 kcfs. Steep watershed most precip is in reservoir within 12 hours of hitting ground. Winter snow pack relied upon for Spring refill. No downstream control point. 5

6 Folsom Dam 6

7 JFP Gate Install 7

8 Main Dam and JFP 8

9 (no inflow) 9

Water Control Diagrams 1,000 Flood Space

Credit 400 200 600 670 JFP + Forecast-based

10 Water Control Diagrams 1,000 Flood Space (TAF) Storage (TAF) Existing (Corps) Basin Wetness Existing (BOR-SAFCA) Upstream Storage Credit JFP + Upstream Credit JFP + Forecast-based Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct 10

11 Forecast-based Operation Components CNRFC ensemble forecasts 6 hour updates Forecast-based top of conservation (TOC) Forecast-based releases 11

12 Forecast-based TOC DRAFT 12

13 Forecast-based TOC DRAFT 13

14 Forecast-based Release 115k 80k 50k 25k Typical American River Cross Section 14

15 Forecast-based Release 15

16 Water Control Diagram 16 DRAFT

17 Routing comparisons 17

18 1986 event pattern scaled to 100-yr Forecast operation reflects perfect forecast Existing (BOR/SAFCA) JFP + US credit JFP + Forecast-based 18

19 1986 event pattern scaled to 200-yr Forecast operation reflects perfect forecast Existing (BOR/SAFCA) JFP + US credit JFP + Forecast-based 19

20 Use of Forecast Ensembles 20

21 Forecast Ensemble 12/22 61 ensemble traces 21

22 Forecast Ensemble 12/23 22

23 Forecast Ensemble 12/24 23

24 Forecast Ensemble 12/25 24

25 Forecast Ensemble 12/26 25

26 Forecast Ensemble 12/27 26

27 Forecast Ensemble 12/28 27

28 Forecast Ensemble 12/29 28

29 Forecast Ensemble 12/30 29

30 Forecast Ensemble 12/31 30

31 Forecast Ensemble 1/1 31

32 Forecast Ensemble 1/2 32

33 Forecast Ensemble 1/3 33

34 Compute Forecasted Inflow Volumes 1-day 2-day 3-day 5-day

35 1997 event hindcast series 3-day volume updated daily 61 ensemble traces 21 probabilistic traces Each trace reflects one value of Non- Exceedence Probability (NEP) 35

36 Robustness Testing Considers uncertainty in forecast indicated by the forecast ensemble. Tests operation using imperfect forecasts. Used to identify operational NEP value. 36

37 Robustness Test Example 1986 event pattern scaled to 200-yr 21 simulations corresponding to NEP values ranging from 0% to 100% (5% increments). Perfect forecast shown as black dashed line for reference. 37

38 Robustness Summary Metric Minimum NEP (%) (1986 / 1997 patterns) Pass 100-yr event at 115 kcfs Pass 200-yr event at 160 kcfs Pass 200-yr event at 160 kcfs (24-hr late forecast) 0% / 0% (ALL PASS) 0% / 0% (ALL PASS) 55% / 60% 38

39 Peak Flow-Frequency DRAFT See handout notes 39

40 Lessons Learned Simple vs. Complex Corps more comfortable with: designated (and limited) variable flood space work within TOC framework demonstrate well-behaved releases 40

41 Moving Forward Draft engineering report complete Agency Technical Review of final report Division / Headquarters / IEPR review 4/15/2017 final signatures 41

42 Questions? 42

FORECAST-BASED OPERATIONS AT FOLSOM DAM AND LAKE

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 Dana on Mission Bay San Diego, CA January 28,