State Water Resources Control Board Order 5/1/2013 Lake Mendocino Water Supply Reliability Evaluation Report Term 17 April 30, 2015 Prepared by Sonoma County Water Agency 404 Aviation Blvd Santa Rosa, CA 95403 LAKE MENDOCINO WATER SUPPLY RELIABILITY EVALUATION REPORT TABLE OF CONTENTS Executive Summary ..................................................................................................................................... 1 1.0 Introduction .......................................................................................................................................... 3 1.1 Purpose and Scope ........................................................................................................................... 3 1.2 Organization of Report ..................................................................................................................... 3 2.0 Background ........................................................................................................................................... 4 2.1 Project History and Description ........................................................................................................ 4 2.2 Flood Management Operations ....................................................................................................... 5 2.3 Water Supply Operations ................................................................................................................. 5 2.4 Potter Valley Project Operations ...................................................................................................... 7 3.0 Methodology ......................................................................................................................................... 8 3.1 Evaluation Scenarios ......................................................................................................................... 9 3.2 Stakeholder Outreach ....................................................................................................................... 9 3.3 Description of Model ......................................................................................................................10 3.4 Model Input ....................................................................................................................................10 3.4.1 System Water Gains ................................................................................................................10 3.4.2 System Water Losses...............................................................................................................11 3.4.3 System Operations ...................................................................................................................12 3.4.4 Municipal Water Use ...............................................................................................................12 3.4.5 Agricultural Water Use ...........................................................................................................14 i 3.5 Key Water Balance Model Assumptions ........................................................................................16 4.0 Model Simulation Results And Observations ......................................................................................16 5.0 Recommendations ..............................................................................................................................18 5.1 Recommended Improvements to Reliability Study ........................................................................18 5.2 Near-Term and Long-Term Activities .............................................................................................19 5.2.1 Initiation and Coordination of Water Conservation Programs ...............................................19 5.2.2 Recycled Water Projects in Healdsburg and Ukiah .................................................................19 5.2.3 Leak Detection and Water Loss Audits ....................................................................................19 5.2.4 Initiation of Routine Meetings among Upper Russian River Water Managers .......................20 5.2.5 Improved Frost and Heat Event Forecasting ...........................................................................20 5.2.6 Evaluation of Forecast Informed Reservoir Operations (FIRO) ...............................................20 5.2.7 Development of a New Hydrologic Index................................................................................20 5.2.8 Evaluation of Raising Coyote Valley Dam ................................................................................21 5.3 Additional Demand Management Measures .................................................................................21 6.0 References ..........................................................................................................................................22 ii LIST OF FIGURES Figure 1. Upper Russian River Watershed Map Figure 2. Lake Mendocino Storage Guide Curve Figure 3. Minimum Instream Flow Requirements per Decision 1610 Figure 4. Cumulative Diversions through Potter Valley Project Figure 5. Water Balance Model Schematic Figure 6. Minimum Instream Flow Requirements with Biological Opinion Interim Changes Figure 7. Municipal Water Use Projections Low Growth Scenario Figure 8. Municipal Water Use Projections High Growth Scenario Figure 9. Upper Russian River Watershed Agricultural Fields circa 2012 Figure 10. Upper Russian River Watershed Current and Projected Total Annual Water Usage Figure 11. Modeling Results – Frequency Distribution of Minimum Annual Reservoir Storage Volumes Figure 12. Modeling Results – Frequency Distribution of Minimum Annual Reservoir Storage Volumes with Climate Change Scenarios LIST OF TABLES Table 1. List of Coordinating Entities Table 2. System Model Evaluation Scenarios Table 3. Water and Land Use Datasets and Records Table 4. Current Municipal Water System Service Populations Table 5. Historical Municipal Water Use (2009-2013) Table 6. Municipal Water Use under Current Conditions (2015) Table 7. Municipal Water Use Projections - Low Growth Scenario Table 8. Municipal Water Use Projections - High Growth Scenario Table 9. Municipal Water Use Projections by River Reach Table 10. Agricultural Irrigation Water Use Crop Duties Table 11. Agricultural Field Acreages by River Reach – Current Conditions iii Table 12. Agricultural Irrigation Water Use by River Reach – Current Conditions Table 13. Frost Protection Water Use Assumptions Table 14. Frost Protection Water Use by River Reach – Current Conditions Table 15. Post-Harvest Water Use by River Reach – Current Conditions Table 16. Projection Assumptions for Crop Land Conversion Table 17. Agricultural Field Acreages by River Reach – Projected 2045 Low Demand Scenario Table 18. Agricultural Field Acreages by River Reach – Projected 2045 High Demand Scenario Table 19. Agricultural Irrigation Water Use by River Reach – Projected 2045 Low Demand Scenario Table 20. Agricultural Irrigation Water Use by River Reach – Projected 2045 High Demand Scenario Table 21. Frost Protection Water Use by River Reach – Projected 2045 Low Demand Scenario Table 22. Frost Protection Water Use by River Reach – Projected 2045 High Demand Scenario Table 23. Post-Harvest Water Use by River Reach – Projected 2045 Low Demand Scenario Table 24. Post-Harvest Water Use by River Reach – Projected 2045 High Demand Scenario LIST OF APPENDICES Appendix A. State Water Resources Control Board Division of Water Rights Order Approving Temporary Urgency Change dated May 1, 2013 Appendix B. Technical Memorandum on Upper Russian River Water Accounting Model iv EXECUTIVE SUMMARY This water supply reliability study of Lake Mendocino (Reliability Study) has been completed by the Sonoma County Water Agency (Water Agency) to fulfill a requirement of the May 1, 2013 Order issued by the State Water Resources Control Board (State Water Board). The Reliability Study evaluates the long-term reliability of Lake Mendocino to meet water supply and environmental water demands. Lake Mendocino is administered by the United States Army Corps of Engineers (Corps) and was formed by the construction of Coyote Valley Dam (CVD) which is located on the East Fork of the Russian River, about 4 miles northeast of the City of Ukiah in Mendocino County. The Corps coordinates releases from CVD during flood management operations. As the local sponsor, the Water Agency controls and coordinates water supply releases from the CVD in accordance with its water rights permits and Decision 1610. In addition to runoff from within its own watershed, Lake Mendocino also receives water from the Eel River through the Potter Valley Project (PVP), a hydroelectric facility located in the headwaters of the East Fork of the Russian River approximately 11 miles upstream of the reservoir. Due to a recent (2006) implementation of a 2004 Federal Energy Regulatory Commission (FERC) license amendment for the PVP, diversions from the Eel River through the PVP have been cut back significantly, which has resulted in a reduced reliability to annually fill Lake Mendocino to adequate levels to meet downstream minimum instream flow requirements and demands. Since 2006, the Water Agency has had to file five Temporary Urgency Change Petitions with the State Water Board to reduce the minimum instream flow requirements downstream of Lake Mendocino in an effort to conserve lake storage for water supply and fisheries