In Cooperation with the California Department of Water Resources, Northern District Lake County Water Inventory and Analysis Final March 2006 Lake County Watershed Protection District Lake County Water Inventory and Analysis March 2006 Final Contents Section 1 Introduction 1.1 Lake County Watershed Protection District.........................................................1-1 1.2 Inventory and Analysis Purpose............................................................................1-2 1.3 Inventory Unit Development..................................................................................1-2 1.4 Document Contents..................................................................................................1-3 Section 2 Physical Setting 2.1 Topography ...............................................................................................................2-1 2.2 Climate .......................................................................................................................2-2 2.2.1 Temperature...............................................................................................2-2 2.2.2 Precipitation ...............................................................................................2-3 2.3 Surface Water Hydrology........................................................................................2-5 2.3.1 Surface Water Flows and Variability......................................................2-5 2.4 Soils...........................................................................................................................2-11 2.5 Geology ....................................................................................................................2-11 2.6 Groundwater Hydrology ......................................................................................2-12 2.6.1 Gravelly Valley Groundwater Basin.....................................................2-13 2.6.2 Upper Lake Basin ....................................................................................2-13 2.6.3 Scotts Valley Basin...................................................................................2-15 2.6.4 Big Valley Groundwater Basin..............................................................2-17 2.6.5 High Valley Basin....................................................................................2-22 2.6.6 Burns Valley Basin ..................................................................................2-23 2.6.7 Coyote Valley Basin ................................................................................2-24 2.6.8 Collayomi Valley Basin ..........................................................................2-26 2.6.9 Lower Lake Basin....................................................................................2-27 2.6.10 Long Valley Groundwater Basin...........................................................2-28 2.6.11 Clear Lake Cache Formation Groundwater Basin..............................2-28 2.6.12 Middle Creek Groundwater Basin........................................................2-29 2.6.13 Clear Lake Volcanics Groundwater Source Area ...............................2-29 2.7 Agricultural Water Demand by Groundwater Basin ........................................2-30 Section 3 Water Management 3.1 Water Sources and Issues ........................................................................................3-1 3.1.1 Surface Water Management.....................................................................3-1 3.1.2 Groundwater..............................................................................................3-4 3.2 Water Management..................................................................................................3-8 3.2.1 Water Management Issues .......................................................................3-9 3.2.1.1 Typical Agricultural Water User Issues..............................3-9 3.2.1.2 Typical Municipal Water User Issues ...............................3-10 3.2.2 Inventory Unit Water Supply and Use.................................................3-11 A i Table of Contents Lake County Water Inventory and Analysis 3.2.2.1 Upper Putah Inventory Unit ..............................................3-12 3.2.2.2 Middle Putah Inventory Unit.............................................3-12 3.2.2.3 Shoreline Inventory Unit ....................................................3-13 3.2.2.4 Thurston Lake Inventory Unit ...........................................3-14 3.2.2.5 Middle Creek Inventory Unit.............................................3-15 3.2.2.6 Scotts Creek Inventory Unit ...............................................3-15 3.2.2.7 Big Valley Inventory Unit...................................................3-16 3.2.2.8 Lower Lake Inventory Unit................................................3-17 3.2.2.9 Cache Creek Inventory Unit...............................................3-18 3.2.2.10 Eel River Inventory Unit.....................................................3-19 3.2.2.11 Lake County Special Districts ............................................3-19 Section 4 Methods and Results 4.1 Water Use and Supply Analysis Methodology....................................................4-1 4.1.1 Water Use Methodology ..........................................................................4-1 4.1.2 Water Supply Methodology.....................................................................4-5 4.2 Definition of Average-, Dry-, and Wet-Year Scenarios .......................................4-6 4.2.1 Average-Year Scenario.............................................................................4-6 4.2.2 Dry-Year Hydrologic Scenario ................................................................4-6 4.2.3 Wet-Year Hydrologic Scenario................................................................4-8 4.3 Summary of Average-Year Inventory ...................................................................4-8 4.3.1 Water Use...................................................................................................4-8 4.3.2 Supplies.....................................................................................................4-10 4.3.3 Net Groundwater Extractions ...............................................................4-12 4.3.4 Shortages...................................................................................................4-13 4.4 Summary of Dry-Year Inventory .........................................................................4-13 4.4.1 Water Use.................................................................................................4-13 4.4.2 Supplies.....................................................................................................4-14 4.4.3 Net Groundwater Extractions ...............................................................4-16 4.4.4 Shortages...................................................................................................4-16 4.5 Summary of Wet-Year Inventory .........................................................................4-16 4.5.1 Water Use.................................................................................................4-17 4.5.2 Water Supplies.........................................................................................4-17 4.5.3 Net Groundwater Extractions ...............................................................4-18 4.5.4 Shortages...................................................................................................4-19 4.6 Environmental and Recreational Water Uses.....................................................4-19 4.6.1 Recreational and Environmental Needs in Clear Lake......................4-19 4.6.2 Environmental Needs on Cache Creek ................................................4-20 4.6.3 Cache Creek Watershed Tributaries .....................................................4-20 4.6.4 Instream Flows for Recreation...............................................................4-21 A ii Table of Contents Lake County Water Inventory and Analysis Section 5 Future Water Use 5.1 Urban Water Use ......................................................................................................5-1 5.1.1 Methods ......................................................................................................5-1 5.1.2 Results.........................................................................................................5-2 5.2 Agricultural Water Use............................................................................................5-3 5.2.1 Methods ......................................................................................................5-3 5.2.2 Results.........................................................................................................5-4 5.3 Environmental and Recreational Water Use ........................................................5-4 5.3.1 Methods ......................................................................................................5-5 5.3.2 Results.........................................................................................................5-5 5.4 Conclusions ...............................................................................................................5-5 Section 6 Conclusions and Recommendations 6.1 Conclusions ...............................................................................................................6-1 6.1.1 Physical