Folsom Dam Water Control Manual Update Joint Federal Project, Folsom Dam Public Workshop May 28, 2015 Library Galleria 828 I Street, Sacramento, CA US Army Corps of Engineers BUILDING STRONG
WELCOME & INTRODUCTIONS 2 05/20/15 CB
PURPOSE OF MANUAL UPDATE Revise operation rules for Folsom Dam to reduce flood risk based on the capabilities of the Folsom Joint Federal Project (JFP). Reflect operational capabilities created by improved weather forecasts. Potentially reduce the volume of flood control reservation in Folsom Reservoir at any particular time by comparison to the operations that have been in effect since 95 3 05/20/15 CB
OBJECTIVES OF MANUAL UPDATE Pass the Probable Maximum Flood while maintaining 3 feet of freeboard below the top of dam to stay within the dam safety constraints of the U.S. Department of Interior, Bureau of Reclamation. Control a 1/100 annual chance flow ( 100-year flood ) to a maximum release of 115,000 cubic feet per second as criteria set by the Sacramento Area Flood Control Agency to support Federal Emergency Management Agency levee accreditation along the American River. Control a 1/200 annual chance flow ( 200-year flood ) as defined by criteria set by the State of California (State) Department of Water Resources to a maximum release of 160,000 cubic feet per second, when taking into account all the authorized modifications within the American River Watershed. 4 05/20/15 CB
TODAY S DISCUSSION Fall Reservoir Drawdown Operations Proposed New Spring Refill Storage Boundary Efforts to Develop & Assess Forecast-Based Alternative Project Milestone Schedule 5 05/20/15 CB
FALL RESERVIOR DRAWDOWN OPERATIONS 6
Fall Drawdown Folsom Lake Water Years 2011 and 2012 30k 10k
WATER CONTROL DIAGRAM REFRESHER 1,000 Flood space (KAF) 0 800 Storage (KAF) 600 Flood space 400 Top of conservation Storage 400 Variable space 600 200 Conservation pool Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct 8
WATER CONTROL DIAGRAM 1,000 800 Storage (KAF) 600 Flood Space (KAF) 0 400 Existing (USACE) 400 KAF Flood Space + Basin Wetness Existing (BOR-SAFCA) 400/670 KAF Flood Space + Upstream Storage Credit Alternative 1 400/600 KAF Flood Space + Upstream Storage Credit Alternatives 2, 3a, 3b 400/600 KAF flood space 400 200 600 670 Alternatives 2, 3a, 3b 400/600 KAF flood space Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct 9
10 PRELIMINARY
FORECAST ALTERNATIVE Preliminary results How it works Assessment 11
100-YR, 1986 PATTERN, EXISTING AND ALTERNATIVES PRELIMINARY 12
200-YR, 1986 PATTERN, EXISTING AND ALTERNATIVES PRELIMINARY PRELIMINARY 13
FORECASTING ALTERNATIVE n-day volumes 62 members n-day volumes probabilistic mean, sd 3A n-day adjusted volumes 3B 14
COMPUTE INFLOW VOLUMES FROM FORECAST ENSEMBLES 1-day 2-day 3-day 4-day 5-day 15
HINDCAST VS INFLOW (3-DAY) 16 Observed refers to model-computed inflows as opposed to hindcast inflows.
HINDCAST VS INFLOW (3-DAY) 17 Observed refers to model-computed inflows as opposed to hindcast inflows.
DRAWDOWN CURVE Defines top of conservation (TOC) based on forecasted inflow volume. Simulations Drawdown curve Gross pool Starting Storage TOC 400 TAF 600 TAF Time Forecasted Inflow Volume Success = do not encroach into surcharge AND peak release <= 115K cfs 18
DRAWDOWN CURVES Target Starting Storage (TOC) Gross pool 400 TAF 600 TAF N-day duration Forecasted Inflow Volume 19
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FORECAST-BASED TOC Forecasted Inflow Volume Days Forecastbased TOC Now 1 2 3 4 5 6 7 400 TAF 600 TAF Days 21
FORECAST-BASED TOC Forecasted Inflow Volume Days Forecastbased TOC 1 2 3 4 5 6 7 Now 400 TAF 600 TAF Days 22
FORECAST-BASED TOC Forecasted Inflow Volume Days Forecastbased TOC 400 TAF 600 TAF Days 1 2 3 4 5 6 7 Now 23
FORECAST-BASED TOC Forecasted Inflow Volume Days Forecastbased TOC 400 TAF 600 TAF 1 2 3 4 5 6 7 Now Days 24
FORECAST-BASED TOC Forecasted Inflow Volume Days Forecastbased TOC 1 2 3 4 5 6 7 Now 400 TAF 600 TAF Days 25
FORECAST-BASED TOC Forecasted Inflow Volume Days Forecastbased TOC 400 TAF 600 TAF 1 2 3 4 5 6 7 Now Days 26
FORECAST-BASED TOC Forecasted Inflow Volume Days Forecastbased TOC 1 2 3 4 5 6 7 Now 400 TAF 600 TAF Days 27
FORECAST-BASED OPERATION Precip / inflow FB TOC Storage START Forecastbased flood operation END 28
FORECAST-BASED RELEASES Forecast duration (days) PRELIMINARY Forecast volume threshold (ac-ft) Maximum Release (cfs) 5 < 300,000 8,000 5 300,000 25,000 3 300,000 50,000 2 300,000 80,000 1 300,000 115,000 29
FORECAST-BASED RELEASES PRELIMINARY 30
1986 PATTERN 25-YR PRELIMINARY 31
1986 PATTERN 100-YR PRELIMINARY 32
1986 PATTERN 200-YR PRELIMINARY 33
1986 PATTERN 100-YR STARTING STORAGE SENSITIVITY PRELIMINARY 34
TENTATIVE ASSESSMENT A forecast-based operations plan appears viable at Folsom Dam. Early results indicate clear benefits over other plans Supportive response from USACE Headquarters Potential significant adverse impacts not apparent Performance trade-offs Frequency of flood operations not yet determined Address potential for not refilling 35
NEXT STEPS Refine based on hindcast-based simulation results and operational considerations Adjust release triggers, magnitudes and rules to avoid impacts, balance trade-offs, and reasonably optimize performance Robust testing under historic and hypothetical hydrologic and operational conditions Additional USACE policy and technical review 36
QUESTIONS? 37
PROJECT MILESTONE SCHEDULE SEPTEMBER 2015 HOLD PUBLIC WORKSHOP JANUARY - FEBRUARY 2016 HOLD PUBLIC WORKSHOP TO: PRESENT AND DISCUSS TENTATIVELY RECOMMENDED ALTERNATIVE FEBRUARY - JULY 2016 USACE PERFORMS FINAL REVIEW USACE COMPLETES DRAFT NEPA / CEQA DOCUMENTS 38
DISCUSSION & QUESTIONS OCT 2017 39