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Northern Sacramento Valley Conjunctive Water Management Investigation Public Workshop

Northern Sacramento Valley Conjunctive Water Management Investigation Public Workshop. December 8, 2010 The Glenn-Colusa Irrigation District and The Natural Heritage Institute. Workshop Objective & Process. Objective Respond to questions from October 21, 2010 workshop 1 Process

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Northern Sacramento Valley Conjunctive Water Management Investigation Public Workshop

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  1. Northern Sacramento Valley Conjunctive Water Management InvestigationPublic Workshop December 8, 2010 The Glenn-Colusa Irrigation District and The Natural Heritage Institute

  2. Workshop Objective & Process • Objective • Respond to questions from October 21, 2010 workshop 1 • Process • Organized questions into topics • Describe each topic • Provide response • Engage in discussion

  3. How Does The Proposed Project Work?

  4. Re-operate Surface Reservoirs with Groundwater “Backstop” • Reservoir re-operation • Additional releases to meet program objectives (North of Delta water supply and environmental enhancement) • Expect reservoir refill from surplus surface flows • Honor existing CVP and SWP delivery obligations and operations constraints • Groundwater operation • Pump groundwater to “repay” reservoirs if storage conditions put contract deliveries or temperature control at risk • Groundwater used in lieu of surface entitlements that then remain in storage • Minimize or avoid GW impacts

  5. Re-Operation Case 1- Reservoir Refills Spring (no inflow) Summer (no inflow) Fall-Winter (inflow) Spring (no inflow) Reservoir Full Target Carryover = 50 Reservoir Full 40 Inflow = 70 Baseline Reservoir Operation 100 100 100 100 100 100 50 8 Flood Release = 20 Deliveries = 50 Target Carryover = 40 Reservoir Full Inflow = 70 Reservoir Full 10 Project Reservoir Operation Flood Release = 10 Deliveries = 60

  6. Re-operation Case 2- Reservoir Does Not Refill Spring (no inflow) Summer (no inflow) Spring (no inflow) Summer (no inflow) Fall-Winter (inflow) Target Carryover = 50 Reservoir Partially Full Target Carryover = 40 Reservoir Full Inflow = 30 40 40 40 100 80 Baseline Reservoir Operation 100 50 80 Deliveries = 50 Flood Release = 0 Deliveries = 40 Reservoir Full Target Carryover = 40 Reservoir Partially Full Target Carryover = 40 Inflow = 30 70 70 10 Project Reservoir Operation Deliveries = 30 Deliveries = 60 Flood Release = 0 Groundwater = 10 40 GW

  7. Project Performance SummaryProject Scenario 2 Evaluated with Revised Model Including Biological Opinions, Forecast-based Operation and Minimum Reservoir Release Criteria

  8. QuestionsHow Does The Proposed Project Work? • Can you do just reservoir re-operation without doing the pumping for repayment? • Where does the water for environmental enhancements and other project benefits come from? • How does the payback water get used? • How do the project benefits compare to the frequency and magnitude of payback?

  9. Questions, continuedHow Does The Proposed Project Work? • How would the reservoir releases be measured? • How would it be determined that water needs to be repaid…what triggers reservoir payback? • Which aquifer are we talking about, the deep or shallow? • Does the study address the total groundwater picture?

  10. Questions, continuedHow Does The Proposed Project Work? • What are the existing contractual obligations? • Public wants assurance that there is adequate thought going into monitoring and mitigation.

  11. Investigation Tools and Data

  12. Overview of Analysis Tools

  13. Groundwater Model Area and Grid Density Chico Orland Unit Butte Basin Willows GCID Sacramento

  14. Groundwater Flow Model • Regional scale with high spatial detail • 5,950 square miles (3.8 million acres) • 88,922 surface nodes • 7 vertical layers • Aquifer properties based on analysis of more than 1,000 production wells • Calibration • Static calibration for year 2000 • Water levels from 257 monitoring wells • Monthly time step, 1982 through 2003

  15. Surface Water Operations Model • Spreadsheet-based for ease and speed of operation • Re-operates Shasta and Oroville Reservoirs relative to a baseline condition depicted by CalSim II outputs (1922 through 2003) • Driven by additional target deliveries for: • Environmental restoration in Sac and Feather Rivers • Unmet Sac Valley agricultural demands • Various operational constraints • Uses generalized SW-GW interaction functions derived from GW model

  16. QuestionsInvestigation Tools and Data • Why are critical dry years not used in the analysis? • What is the time-step used to develop the groundwater model? Is the time-step appropriate for capturing localized effects of day to day well operation and aquifer response? • Were economic impacts beyond just project costs and benefits considered, such as impacts to specific segments of the agricultural community?

  17. Project Benefits

  18. QuestionsProject Benefits • What are the project benefits? • Are there benefits to the groundwater systems and were they considered in the economic analysis?

  19. Project Benefits • Increased Sac Valley surface water supply • More local benefit (water supply) from CVP and SWP • Reduced overall reliance on Sac Valley groundwater, though increased local pumping in certain years • Improved habitat in Sac and Feather Rivers through • Recovery of salmon populations • Ecosystem sustainability

  20. Project Impacts

  21. QuestionsProject Impacts • What are the impacts of groundwater pumping in the valley on foothill aquifers? • What are the critical recharge months in the upper reaches? In the area in general? • Project pumping may be a small share of Valley wide pumping but what proportion is it of pumping within the project area?

  22. Typical Sacramento Valley GW Hydrograph (Butte Co.)

  23. Sacramento Valley Water Uses and Sources by County

  24. Peak Year Project Pumping (100 TAF1) in Relation to Estimated Annual Baseline Pumping 1 Peak year project pumping is 100 TAF in the Butte Basin and in GCID but the two not occur in the same year based on the 1922 through 2003 modeling

  25. QuestionsProject Impacts • Is the interconnection between streams and underlying aquifers sufficiently defined to predict the effects of even modest changes in groundwater levels (e.g., Butte and Big Chico Creeks)?

  26. Questions, continuedProject Impacts • What is the extent of the impact on domestic (and other wells)? You show 0 to 6 feet, but you also say that near the wells that are pumping payback water it could be 50 or 60 feet? Even a few feet can have a large impact. This needs to be clarified.

  27. Comparison of Drawdown from Modeling and Averaged for Impact Analysis Regional Aquifer Drawdown in Aug 1990 , Scenario 1, New Well Field Potential Impact Zones: Worst Case, New Wells Figure 11-15, p.11-16 from Modeling Report, Feb 2010

  28. Next Steps • Draft and Final Investigation Report • Additional public meetings • Phase 2

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