Groundwater availability of the central valley aquifer, california

1.GROUNDWATER RESOURCES PROGRAMGroundwater Availability of theCentral Valley Aquifer, CaliforniaSacramento ValleySan Joaquin ValleyProfessional Paper 1766U.S. Department of the InteriorU.S. Geological Survey

2. Generalized block diagrams showing post-development hydrologeology of the Sacramento and San Joaquin Valleys, California. 3. Groundwater Availability of theCentral Valley Aquifer, CaliforniaEdited by Claudia C. FauntChapter AIntroduction, Overview of Hydrogeology, and Textural Model ofCalifornias Central ValleyBy Claudia C. Faunt, Randall T. Hanson, and Kenneth BelitzChapter BGroundwater Availability in Californias Central ValleyBy Claudia C. Faunt, Kenneth Belitz, and Randall T. HansonChapter CNumerical Model of the Hydrologic Landscape and GroundwaterFlow in Californias Central ValleyBy Claudia C. Faunt, Randall T. Hanson, Kenneth Belitz, Wolfgang Schmid,Steven P. Predmore, Diane L. Rewis, and Kelly McPhersonAppendix 1Supplemental InformationModifications toModflow-2000 Packages and ProcessesBy Wolfgang Schmid and R.T. HansonGroundwater Resources ProgramProfessional Paper 1766U.S. Department of the InteriorU.S. Geological Survey 4. U.S. Department of the InteriorKEN SALAZAR, SecretaryU.S. Geological SurveySuzette M. Kimball, Acting DirectorU.S. Geological Survey, Reston, Virginia: 2009For more information on the USGSthe Federal source for science about the Earth, its natural and living resources,natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGSFor an overview of USGS information products, including maps, imagery, and publications,visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.govAny use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S.Government.Although this report is in the public domain, permission must be secured from the individual copyright owners toreproduce any copyrighted materials contained within this report.Suggested citation:Faunt, C.C., ed., 2009, Groundwater Availability of the Central Valley Aquifer, California: U.S. Geological SurveyProfessional Paper 1766, 225 p.ISBN 978-1-4113-2515-9 5. iiiForewordAn adequate supply of groundwater is essential for the Nations health and economic wellbeing. Increased use of groundwater resources and the effects of drought have led to concernsabout the future availability of groundwater to meet domestic, agricultural, industrial, and envi-ronmental needs. The resulting effects of competition for groundwater from human and environ-mental uses need to be better understood to respond to the following basic questions that arebeing asked about the Nations ability to meet current and future demands for groundwater. Dowe have enough groundwater to meet the needs of the Nation? Where are these groundwaterresources? Is groundwater available where it is needed? To help answer these questions, theU.S. Geological Surveys (USGS) Groundwater Resources Program is conducting large-scalemultidisciplinary regional studies of groundwater availability, such as this study of the CentralValley Aquifer System, California.Regional groundwater availability studies quantify current groundwater resources, evaluate howthose resources have changed through time, and provide tools that decision makers can useto forecast system responses to future development and climate variability and change. Thesequantitative studies are, by design, large in scope, can include multiple aquifers, and addresscritical groundwater issues. The USGS has previously identified the Nations principal aquifersand they will be used as a framework to classify and study regional groundwater systems.The groundwater availability studies being conducted for each regional groundwater flow sys-tem emphasize the use of long-term groundwater monitoring data, in conjunction with ground-water models, to improve understanding of the flow systems and assess the status and trendsin groundwater resources in the context of a changing water budget for the aquifer system. Theresults of these individual groundwater availability studies will be used collectively as buildingblocks towards a national assessment of groundwater availability. In addition, these studies willprovide the foundational information and modeling tools needed to help State and local resourcemanagers make water availability decisions based on the latest comprehensive quantitativeassessment given their regional water-management constraints and goals.Matthew C. Larsen, Associate Director for WaterU.S. Geological Survey 6. iv This page intentionally left blank. 7. vContentsChapter AIntroduction, Overview of Hydrogeology, and Textural Model of Californias Central ValleyExecutive Summary .......................................................................................................................................1 Geographic Information System (GIS) ..............................................................................................1 Texture Modeling ..................................................................................................................................2 Hydrologic System Modeling ..............................................................................................................2Introduction.....................................................................................................................................................3 Purpose and Scope ..............................................................................................................................4 Methods of Analyses............................................................................................................................6Data Compilation ..........................................................................................................................6Numerical Model .........................................................................................................................6 Previous Investigations........................................................................................................................7Recent Regional Groundwater Models ....................................................................................7 Central Valley Regional Aquifer-System Analysis (CV-RASA) ....................................7 California Central Valley Groundwater-Surface-Water Simulation Model (C2VSIM) ..............................................................................................................10Study Area.....................................................................................................................................................10 Climate .................................................................................................................................................10 Sacramento Valley .............................................................................................................................10 Delta and Eastside Streams ..............................................................................................................15 San Joaquin Basin of the San Joaquin Valley ...............................................................................15 Tulare Basin of the San Joaquin Valley ..........................................................................................17 Water-Balance Subregions...............................................................................................................18Geologic History and Setting .....................................................................................................................18Hydrogeology................................................................................................................................................20 Aquifer Characteristics ......................................................................................................................20 Textural Analysis .................................................................................................................................23Selection and Compilation of Existing Well Data .................................................................25Classification of Texture from Drillers Logs and Regularization of Well Data ................26Geostatistical Modeling Approach .........................................................................................26 Regions and Domains ......................................................................................................26 Geostatistical Model of Coarse-Grained Texture ........................................................27 3-D Model of Percentage of Coarse-Grained Texture ................................................29Results of Texture Model ..........................................................................................................30 Sacramento Valley............................................................................................................30 San Joaquin Valley ...........................................................................................................39 Hydrologic System ..............................................................................................................................40Climate ........................................................................................................................................41Surface Water ............................................................................................................................46 8. viGroundwater ..............................................................................................................................47 Predevelopment Recharge, Discharge, Water Levels, and Flows ...........................48 Groundwater/Surface-Water Interaction .....................................................................48 Aquifer-System Storage ..................................................................................................48 Water Budget ....................................................................................................................53 Acknowledgments .......................................................................................................................................53 References Cited..........................................................................................................................................54 Chapter B Groundwater Availability in Californias Central Valley Introduction ..................................................................................................................................................59 Development and the Hydrologic System ...............................................................................................59Surface-Water and Groundwater Development History .............................................................59Land Use ...............................................................................................................................................60 Agricultural Land Use ...............................................................................................................61 Urban Land Use ..........................................................................................................................61 Development and Changes to the Hydrologic Budget ..........................................................................62Hydrologic Budget Components ......................................................................................................62 Recharge and Discharge ..........................................................................................................66 Aquifer-System Storage ...........................................................................................................67 Intra-Annual Variations in Typical, Dry, and Wet Years.......................................................70Temporal Variation in the Hydrologic Budget ...............................................................................72Spatial Variation in the Hydrologic Budget ....................................................................................79Water Levels and Groundwater Flow .............................................................................................79Land Subsidence.................................................................................................................................98Surface Water and the Environment .............................................................................................101 Global Climate Change and Variability ...................................................................................................102Past Climates .....................................................................................................................................102Future Climate Projections ..............................................................................................................102 Groundwater Sustainability and Management ....................................................................................103Groundwater Sustainability ............................................................................................................103Groundwater Management ............................................................................................................104 Conjunctive Use .......................................................................................................................106 Water Banking..........................................................................................................................107 Other Management Strategies ..............................................................................................108 Monitoring the Hydrologic System .........................................................................................................109Groundwater ......................................................................................................................................110Surface Water ...................................................................................................................................111Subsidence ........................................................................................................................................112Water Quality .....................................................................................................................................112Land Use and Climate.......................................................................................................................114 Summary......................................................................................................................................................114 References Cited........................................................................................................................................116 9. viiChapter CNumerical Model of the Hydrologic Landscape and Groundwater Flow inCalifornias Central ValleyIntroduction ................................................................................................................................................121Model Development ..................................................................................................................................121 Discretization ....................................................................................................................................123 Spatial Discretization and Layering ......................................................................................123 Temporal Discretization .........................................................................................................126 Boundary Conditions .......................................................................................................................126 Specified-Flow Boundaries ....................................................................................................128 Pumpage ...................................................................................................................................128 Agricultural Pumpage ....................................................................................................128 Urban Pumpage ..............................................................................................................130 Recharge from and Discharge to the Delta .........................................................................131 Recharge from and Discharge to Canals and Streams .....................................................132 Water-Table Simulation ...................................................................................................................132 Farm Process (FMP) .........................................................................................................................132 Delivery Requirement ..............................................................................................................134 Soils ..............................................................................................................................135 Land Use ...........................................................................................................................135Virtual Crop Maps ..................................................................................................139Crop-Type Data.......................................................................................................143 Climate Data ....................................................................................................................151Reference Evapotranspiration (ETo) ...................................................................151Precipitation ...........................................................................................................152 Surface-Water Supply ............................................................................................................152 Groundwater Supply ...............................................................................................................152 Net Recharge ...........................................................................................................................154 Hydraulic Properties.........................................................................................................................154 Hydraulic Conductivity ............................................................................................................156 Storage Properties ..................................................................................................................158 Hydrogeologic Units ...............................................................................................................160 Hydrogeologic Structures .....................................................................................................160 Initial Conditions................................................................................................................................160Model Calibration and Sensitivity ...........................................................................................................161 Observations Used in Model Calibration ......................................................................................161 Water-Level Altitudes, Water-Level Altitude Changes, andWater-Level Altitude Maps .......................................................................................163 Water-Table and Potentiometric-Surface Maps .......................................................167Sacramento Valley.................................................................................................167Delta .....................................................................................................................167San Joaquin Valley ...............................................................................................170Tulare Basin ............................................................................................................170 Streamflow Observations .......................................................................................................170 Boundary Flow Observations .................................................................................................173 10. viii Subsidence Observations ......................................................................................................173 Pumpage Observations ...........................................................................................................179 Water-Use Observations ........................................................................................................179 Water-Delivery Observations.................................................................................................181Model Parameters ...........................................................................................................................181Sensitivity Analysis ..........................................................................................................................191 Simulation Results and Budget ...............................................................................................................191Recharge and Discharge .................................................................................................................192Aquifer-System Storage ..................................................................................................................197 Model Uncertainty and Limitations ........................................................................................................203 Future Work ................................................................................................................................................205 References Cited........................................................................................................................................207 Appendix 1 Supplemental InformationModifications to Modflow-2000 Packages and Processes Introduction.................................................................................................................................................213 Layer-Property Flow Package (LPF) .......................................................................................................213 Multiplier Package (MULT).......................................................................................................................213 Time-Series Package (HYDMOD) ............................................................................................................213 Streamflow Routing Package (SFR1) ......................................................................................................214 The Farm Process (FMP1) ........................................................................................................................214Concepts and Input Instructions for New FMP1 Features ........................................................214Data for each Simulation ........................................................................................................215Data for each Stress Period ...................................................................................................216Root Uptake Under Variably Saturated Conditions (PSI specified in Item 14)........................217Current Concept of Root Uptake from Unsaturated Conditions .......................................217Expanded Concept of Root Uptake from Variably Saturated Conditions........................217Input Instructions .....................................................................................................................221Matrix of On-Farm Efficiencies (OFE specified in Items 7 or 24) ...............................................221Input Requirements .................................................................................................................221Data Output ...............................................................................................................................221Non-Irrigation Crops (NONIRR Specified in Items 15 or 27) ......................................................222Consumptive Use Options (ICUFL Specified in Item 2; ETR Specified as New Item) ............222Semi-Routed Delivery (ISRDFL in Item 2; REACH in Items 20 or 34) .........................................222Semi-Routed Surface-Water Runoff-Return Flow (ISRRFL in Item 2 and ROW COLUMNSEGMENT REACH Specified as New Item) ....................................................................223Farm-Related Data List for Semi-Routed Runoff-Return Flow Locations(New Item Added After Items 20 or 34): ........................................................223Additional Auxiliary Variable (AUX NOCIRNOQ Specified in Item 2) .......................................224Farm Budget Output Options (IFBPFL Specified in Item 2) ........................................................224 References Cited........................................................................................................................................225 11. ixFiguresChapter AFigure A1.Map of Central Valley major geomorphic provinces, alluvial fans of theSan Joaquin Basin, and extent and thickness of Corcoran Clay ....................................5Figure A2.Diagram showing the relation and flow of information used in analyzing theCentral Valley Hydrogeologic system .................................................................................7Figure A3.Diagram showing the diversity of data types and categories included in thecentralized geospatial database ..........................................................................................8Figure A4. Diagram showing an example of the detail for compilation, integration, andanalysis for one data type (water-level nformation) .........................................................9Figure A5.A, Map of surface-water inflows and average annual precipitation forSeptember 1961 through September 2003 throughout the Central Valley,California. B, Map showing average annual reference evapotranspiration (ETo)for September 1961 through September 2003 throughout the Central Valley,California ................................................................................................................................12Figure A6.Graph of average monthly precipitation for Redding, Davis, andBakersfield, California ..........................................................................................................14Figure A7.Map of general features of the surface-water system in the CentralValley, California ....................................................................................................................16Figure A8.Map of distribution of water-balance subregions (WBSs) used forsurface-water delivery and estimation of groundwater pumpage ...............................19Figure A9.Generalized cross-sections showing pre- and post-development of theA, Sacramento Valley. B, Central part of the San Joaquin Valley,California.................................................................................................................................21Figure A10. A, Map of Central Valley showing groundwater basins and subbasins,groupings of basins and subbasins into spatial provinces and domains fortextural analysis. B, Map showing distribution of wells used for mapping texture.C, Graph showing count of wells for each depth increment by domains through 1,200 feet .................................................................................................................24Figure A11.Generalized hydrogeologic section (AA) indicating the vertical discretizationof the numerical model of the groundwater-flow system in the Central Valley,California ................................................................................................................................29Figure A12.Maps showing kriged distribution of coarse-grained deposits for layers 1, 3,Corcoran Clay, 6, and 9 of the groundwater-flow model. A, Layer 1. B, Layer 3.C, Corcoran Clay. D, Layer 6. E, Layer 9 .............................................................................31Figure A13.Block diagram of kriged texture within groundwater-flow model ..............................36Figure A14.Map showing distribution of coarse-grained deposits for the upper 50 feet for part of the Central Valley...............................................................................................37Figure A15.Graph of cumulative distributions of kriged sediment textures for model layers in the A, Sacramento Valley. B, San Joaquin Valley and Tulare Basin ...........38Figure A16. A, Bar chart of total inflow from 44 gaged streams flowing into the Central Valley, California, water years 19622003. B, Graph of average annual precipitation in the Central Valley, California, water years 19622003. C, Pie chart of total surface-water flow into the Central Valley, California, water years 19622003 .......................................................................................................42 12. xFigure A17. Graph of cumulative departure from average annual precipitation atRedding, Davis, Fresno, and Bakersfield, California ......................................................44Figure A18. Graph of cumulative departure of monthly precipitation (Parameter-elevation Regressions on Independent Slopes Model (PRISM) data from Davis,California), cumulative departure of the Pacific Decadal Oscillation (PDO)index, and cumulative departure of the monthly reference evapotranspiration(ETo) values (gridded values of California Irrigation Management InformationSystems (CIMIS) stations from Redding, Davis, and Bakersfield, 19602004) .........45Figure A19. Graph of cumulative departure of streamflow diversions from theBear River by South Sutter Water District, California; cumulative annualtemperature from California Irrigation Management Information Systems(CIMIS) stations at Davis and the Pacific Decadal Oscillation (PDO) index,19602004 ..............................................................................................................................47Figure A20. Map of pre-development groundwater map ....................................................................49Figure A21. Maps of distribution of A, Pre-1900 land-use patterns. B, Land-usepatterns in 2000 for the Central Valley, California ...........................................................50Figure A22. Map of distribution of selected streams and canals, and averageestimated gains and losses for selected segments .......................................................52Figure A23. Diagrams of pre-development water budget and post-developmentwater budget .........................................................................................................................53Chapter BFigure B1.Diagram showing average water budget for water years 19622003 .........................63Figure B2.Pie charts and histograms showing simulated landscape budget for theCentral Valley for typical (1975), dry (1990), and wet (1998) years ...............................64Figure B3. Pie charts and histograms showing simulated groundwater budget for theCentral Valley for typical (1975), dry (1990), and wet (1998) years ...............................65Figure B4. Maps of A, Estimated change in hydraulic head in upper part of theaquifer system from 1860 to 1961. B, Simulated change in hydraulic head inlower part of the aquifer system from spring 1962 to spring 2003 ...............................68Figure B5. Graphs showing monthly groundwater budget for the Central Valley for adry year (1990), typical year (1975), and wet year (1998) ...............................................71Figure B6. Graphs of annual A, Delivery requirement, landscape recharge,surface-water deliveries, and agricultural pumpage. B, Groundwaterwithdrawals for agricultural and urban use for the entire Central Valleybetween 1962 and 2003 .......................................................................................................73Figure B7. Stacked bar chart showing simulated groundwater budget changes betweenwater years 1962 and 2003 for the Central Valley, California ........................................75Figure B8. Stacked bar chart showing simulated annual changes in aquifer-systemstorage between water years 1962 and 2003 for the Central Valley, California .......76Figure B9. Graph showing simulated cumulative annual changes in aquifer-system storagebetween water years 1962 and 2003 for the Central Valley, California ......................77Figure B10. Pie charts and histograms of average annual groundwater budget for theA, Sacramento Valley. B, Delta and Eastside Streams. C, San Joaquin Valley.D, Tulare Basin .....................................................................................................................80Figure B11. Stacked bar chart of simulated flow through multi-zone wells ...................................84 13. xiFigure B12. Map of altitude of the A, Water table in the unconfined part of the aquifer system. B, Potentiometric surface of the confined part of the aquifer system for1961. C, Unconfined part of the aquifer system. D, Potentiometric surface of the confined part of the aquifer system for 1976. E, Unconfined part of the aquifer system. F, Potentiometric surface of the confined part of the aquifer system, for 2000 .....................................................................................................86Figure B13. Map showing hydrographs for representative wells in the Central Valley, California................................................................................................................................92Figure B14. Map of estimated depth to water table in spring 2000 ...................................................96Figure B15. A, Map of areal extent of land subsidence in the Central Valley and locations of extensometers. B, Graph of compaction data from selected extensometers and total simulated pumpage in the Central Valley ............................99Figure B16. Graph of measured compaction in relation to head decline in the San Joaquin Valley.............................................................................................................101Figure B17. Graph showing streamflow gains and losses in the Central Valley between 1962 and 2003 .....................................................................................................105Figure B18. Diagram of relationship of water-level changes and critical heads to subsidence and inelastic compaction ...........................................................................109Chapter CFigure C1.Map of Central Valley Hydrologic Model grid: A, Extent of San JoaquinFormation, Corcoran Member of the Tulare Formation, crystalline bedrock,and horizontal flow barriers. B, Upper-most active layer............................................124Figure C2. Map of distribution of general-head boundary cells and major streamsand canals with streamflow-routing cells (including location of inflows anddiversions) ...........................................................................................................................127Figure C3. Map of distribution of urban and agricultural wells simulated in theCentral Valley Hydrologic Model ....................................................................................129Figure C4. Graph of urban pumpage from U.S. Geological Survey and CaliforniaDepartment of Water Resources data ............................................................................131Figure C5. Flow chart of water inflows to and outflows from a farm as simulatedby the Farm Process (FMP) .............................................................................................133Figure C6. Map of agricultural soils for the Central Valley, California, derived fromSTATSGO data ....................................................................................................................136Figure C7. Graph showing cumulative departure of precipitation, Pacific DecadalOscillation (PDO) Index, climate windows, and time frame land-use mapswere applied .......................................................................................................................137Figure C8. Map showing virtual crops for 1960 (modified with 2000 data), includingpie chart of percentage of different virtual crops ........................................................140Figure C9. Map showing virtual crops for 1973, including pie chart of percentage ofdifferent virtual crops ........................................................................................................141Figure C10. Map showing virtual crops for 1992, including pie chart of percentage of different virtual crops .......................................................................................................142Figure C11. Map showing virtual crops for 1998, including pie chart of percentage of different virtual crops .......................................................................................................144 14. xiiFigure C12. Map showing virtual crops for 2000, including a pie chart of percentage ofdifferent virtual crops .......................................................................................................145Figure C13. Graphs showing monthly crop coefficients for virtual crops in theCentral Valley, California ..................................................................................................147Figure C14. Graph showing relation between hydraulic conductivity and percentagecoarse-grained deposits based on hydraulic conductivity end members andexponent of the power mean ..........................................................................................155Figure C15. Map of distribution of calibration data (groundwater levels, gains and losses of streamflow, and subsidence observations)................................................162Figure C16. Map of distribution of wells with water-level-altitude data for thesimulation period 19612003, and location of wells selected for modelcalibration ..........................................................................................................................164Figure C17. Graph of plots of simulated water-level altitude values compared with themeasured water-level altitudes for the A, Entire modeled area (and with insetwith histogram of residuals). B, Sacramento Valley. C, Delta and Eastside.D, San Joaquin Basin. E, Tulare Basin ..........................................................................165Figure C18. Maps of the simulated A, Water-table altitude in spring 1976.B, Potentiometric-surface altitude in spring 1976 for the calibrated transientgroundwater-flow model of the Central Valley ............................................................168Figure C19. Map showing distribution of stream gain/loss segments used for modelcalibration A, Measured gaining and losing reaches for selected streamreaches for 19611977. B, Simulated gaining and losing reaches forselected stream reaches for 19611977 for the Central Valley, California ..............171Figure C20. Map of distribution of historical subsidence, estimated from 1961 to1977 extensometer data, Central Valley, California .....................................................174Figure C21. A, Map of distribution of total simulated subsidence for water years1962 through 2003, and locations of subsidence measurements. B, Graphof aggregate compaction measured at, and simulated subsidence for,selected extensometer locations, Central Valley, California .....................................175Figure C22. Graph of agricultural pumpage from 196177 estimated from powerrecords compared to Central Valley Hydrologic Model simulated agriculturalpumpage for the Central Valley, California ...................................................................180Figure C23. Graph showing A, Annual water deliveries. B, Monthly water deliveriesfrom the mid 1970s to mid 1980s for water-balance subregion 14 ............................182Figure C24. Graph showing single and double cropped crop coefficient values fortruck crops .........................................................................................................................183Figure C25. Graph showing original and adjusted crop coefficient values for truck andcotton crops .......................................................................................................................184Figure C26. Map showing distribution of cells used for streams, colored by streambedhydraulic conductivity values for cells estimated during calibration ......................190Figure C27. Graph showing relative composite sensitivity of computed water-levelaltitudes, flows, and subsidence information at calibration points to changesin parameters.....................................................................................................................192 15. xiiiFigure C28. Pie chart and histograms showing average annual components of farmbudget for water years 19622003 .................................................................................193Figure C29. Stacked bar chart showing farm budget changes through time for theCentral Valley, California ..................................................................................................194Figure C30. Graphs showing farm budget changes through time for water-balancesubregion 13, western San Joaquin Valley, Central Valley, California.A, Water years 19622003. B, Water years 19771985 ...............................................195Figure C31. Stacked bar chart showing groundwater budget changes through timefor the Central Valley. A, All values. B, Net values ......................................................197AppendixFigure 1-1. Diagram of evaluation of active and inactive parts of a variablysaturated root zone in FMP .............................................................................................218Figure 1-2. Diagram of conceptualization to the change of transpiration uptakefrom a saturated root zone with varying water level ..................................................220 16. xivTablesChapter ATable A1. Water-balance subregions within the Central Valley, California ...................................11Table A2. Distribution of statistical properties for the percentage of coarse-graineddeposits for the Central Valley, Calfornia, by domain, including variogram andvariogram models ....................................................................................................................28Table A3. Central Valley, California, groundwater flow model layer thicknesses and depths ....29Chapter BTable B1. Summary of the simulated landscape budget for average (water years1962-2003), typical (1975), dry (1990), and wet (1998) years for the Central Valley,California ..................................................................................................................................66Table B2. Summary of the simulated groundwater budget for average (water years1962-2003), typical (1975), dry (1990), and wet (1998) years for the Central Valley,California ..................................................................................................................................66Table B3. Selected average annual hydrologic budget components for water years19622003 for each of the 21 water balance areas in the Central Valley,California ..................................................................................................................................78Chapter CTable C1. MODFLOW-2000 packages and processes used with the hydrologic flowmodel of the Central Valley, California ...............................................................................122Table C2. Coordinates of the Central Valley Hydrologic Model grid ..............................................126Table C3. Land-use periods with acreage in square miles and percentage ofdifferent virtual crop categories .........................................................................................138Table C4. Summary of Central Valley, California, virtual crop categories and properties .........146Table C5. Summary of fractions of transpiration and evaporation by month forCentral Valley, California, virtual crops .............................................................................150Table C6. Average area-weighted composite efficiency for each water-balancesubregion of the Central Valley, California, through the simulation period .................151Table C7. Average reference evapotranspiration (ETo) by month for the Central Valley,California, for 19612003 based on temperature data using the HargreavesSamani equation ....................................................................................................................153Table C8. Measured and simulated hydraulic properties ................................................................157Table C9. Estimated and Central Valley Hydrologic Model-simulated average and unitevapotranspiration of applied water (ETaw) for the Central Valley, California ..........180Table C10.Parameter values estimated for the Central Valley Hydrologic Model ........................185Table C11.Simulated farm budget for the Central Valley, California, in acre-feet per year ........199Table C12.Simulated groundwater budget for the Central Valley, California,in acre-feet per year ............................................................................................................200 17. xvConversion FactorsInch/Pound to SI Multiply By To obtain Length inch (in.)2.54centimeter (cm) inch (in.)25.4millimeter (mm) foot (ft) 0.3048meter (m) mile (mi) 1.609 kilometer (km) mile, (mi)1.609 kilometer (km)Area acre 4,047square meter (m2) acre0.4047hectare (ha) acre0.4047square hectometer (hm2) acre0.004047square kilometer (km2) square foot (ft2)929.0square centimeter (cm2) square foot (ft2) 0.09290 square meter (m2) square inch (in2) 6.452 square centimeter (cm2) section (640 acres or 1 square mile) 259.0square hectometer (hm2) square mile (mi2)259.0hectare (ha) square mile (mi2) 2.590 square kilometer (km2) Volume acre-foot (acre-ft)1,233cubic meter (m3) acre-foot (acre-ft) 0.001233cubic hectometer (hm3)Flow rate acre-foot per day (acre-ft/d) 0.01427 cubic meter per second (m3/s) acre-foot per year (acre-ft/yr)1,233cubic meter per year (m3/yr) acre-foot per year (acre-ft/yr) 0.001233cubic hectometer per year (hm3/yr)Hydraulic conductivity foot per day (ft/d) 0.3048meter per day (m/d)Temperature in degrees Celsius (C) may be converted to degrees Fahrenheit (F) as follows:F=(1.8C)+32Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929(NGVD 29).Altitude, as used in this report, refers to distance above or below the NGVD 29.NGVD 29 can be converted to the North American Vertical Datum of 1988 (NAVD 88) by using theNational Geodetic Survey conversion utility available at URL http://www.ngs.noaa.gov/TOOLS/ 18. xviWell-Numbering System Wellsareidentifiedandnumberedaccordingtotheirlocationintherectangularsystemforthesubdivi-sionofpubliclands.Identificationconsistsofthetownshipnumber,northorsouth;therangenumber,eastorwest;andthesectionnumber.Eachsectionisdividedintosixteen40-acretractsletteredconsecutively(exceptIandO),beginningwith"A"inthenortheastcornerofthesectionandprogressinginasinusoidalmannerto"R"inthesoutheastcorner.Withinthe40-acretract,wellsaresequentiallynumberedintheordertheyareinven-toried.Thefinalletterreferstothebaselineandmeridian.InCalifornia,therearethreebaselinesandmerid-ians;Humboldt(H),MountDiablo(M),andSanBernardino(S).AllwellsinthestudyareaarereferencedtotheSanBernardinobaselineandmeridian(S)Wellnumbersconsistof15charactersandfollowtheformat011N001E24Q008S.Inthisreport,wellnumbersareabbreviatedandwritten11N/1E-24Q8.Wellsinthesametownshipandrangearereferredtoonlybytheirsectiondesignation,24Q8.Thefollowingdiagramshowshowthenumberforwell11N/1E-24Q8isderived. RANGE R2W R1W R1E R2E R3E SECTION 24T13NR1EDCBA Mt. Diablo Meridian654 321T12N EFGH TOWNSHIP789 10 11 12T11N ML K J18 17 1615 14 13T10N T11N19 20 2122 23 24 NPQRT9N30 29 2827 26 2531 32 3334 35 36 11N/1E-24Q8Well-numbering diagram (Note: maps in this report use abbreviated well numbers such as "24Q8") 19. Chapter A. Introduction, Overview of Hydrogeology, and TexturalModel of Californias Central ValleyBy Claudia C. Faunt, Randall T. Hanson, and Kenneth Belitz isatoolreferredtoastheCentralValleyHydrologicModelExecutive Summary(CVHM)thataccountsforintegrated,variablewatersupply anddemand,andsimulatessurface-waterandgroundwater-CaliforniasCentralValleycoversabout20,000square flowacrosstheentireCentralValleysystem.milesandisoneofthemostproductiveagriculturalregions ThedevelopmentoftheCVHMcomprisedfourmajorintheworld.Morethan250differentcropsaregrowninthe elements:(1)acomprehensiveGeographicInformationCentralValleywithanestimatedvalueof$17billionperyear. System(GIS)tocompile,analyzeandvisualizedata;(2)aThisirrigatedagriculturereliesheavilyonsurface-waterdiver- texturemodeltocharacterizetheaquifersystem;(3)estimatessionsandgroundwaterpumpage.Approximatelyone-sixthof ofwater-budgetcomponentsbynumericallymodelingthetheNationsirrigatedlandisintheCentralValley,andabout hydrologicsystemwiththeFarmProcess(FMP);and(4)one-fifthoftheNationsgroundwaterdemandissuppliedfrom simulationstoassessandquantifyhydrologicconditions.its aquifers.TheCentralValleyalsoisrapidlybecominganimportantareaforCaliforniasexpandingurbanpopulation.Since1980, Geographic Information System (GIS)thepopulationoftheCentralValleyhasnearlydoubledfrom2millionto3.8millionpeople.TheCensusBureauprojectsTheGISfortheCVHMisusedtostore,analyze,link,thattheCentralValleyspopulationwillincreaseto6million andvisualizeboththespatialandtemporalmodelinputpeopleby2020.Thissurgeinpopulationhasincreasedtheandoutputdata.Becausethethree-dimensional(3-D)competitionforwaterresourceswithintheCentralValleyand groundwater-flowmodeloftheheterogeneousCentralValleystatewide,whichlikelywillbeexacerbatedbyanticipatedaquifersystemincludescomplexsurface-watermanagementreductionsindeliveriesofColoradoRiverwatertosouthernprocesses,theGISisextremelyusefulforrecognizingandCalifornia.Inresponsetothiscompetitionforwater,anumber understandingspatialrelationswithinandbetweendatasets.ofwater-relatedissueshavegainedprominence:conservationBecausedatatransformation(includingmathematicalfunc-ofagriculturalland,conjunctiveuse,artificialrecharge,hydro- tionsorlogicaloperations),reformatting,andintegrationlogicimplicationsofland-usechange,andeffectsofclimate areaccomplishedrelativelyeasilyusingGISs,theCVHMvariability.GISwasextremelyvaluabletothehydrologicmodeling.InToprovideinformationtostakeholdersaddressingthese particular,theCVHMGISwasusedtoassistintheconversionissues,theUSGSGroundwaterResourcesProgrammadea ofremotelysensedland-useinformationandtopographyfromdetailedassessmentofgroundwateravailabilityoftheCentraldigitalelevationmodelsintoinputtothegroundwatermodel.Valleyaquifersystem,thatincludes:(1)thepresentstatusof ThelinkbetweenthegroundwatermodelandtheGIS,how-groundwaterresources;(2)howtheseresourceshavechanged ever,wasaccomplishedwiththeaidofcomputerprogramsforovertime;and(3)toolstoassesssystemresponsestostresses translatinginputandoutputdata.Informationfrommultiple,fromfuturehumanusesandclimatevariabilityandchange.oftendisparate,datasetswerecombined,processed,and(or)Thiseffortbuildsonpreviousinvestigations,suchastheresampled to produce spatial and temporal data sets needed forUSGSCentralValleyRegionalAquiferSystemandAnalysisthegroundwatermodelinputand(or)observations.In(CV-RASA)projectandseveralothergroundwaterstudiesinaddition,thegroundwatermodelresultscanbereadilytheValleycompletedbyFederal,StateandlocalagenciesatvisualizedspatiallyandtemporallyusingtheCVHMGISanddifferingscales.Theprincipalproductofthisnewassessmentaccompanyingtranslationprograms. 20. 2 Groundwater Availability of the Central Valley Aquifer, CaliforniaTexture Modelingvalleyhaslowerelevationdrainagebasinsandisdrainedinter-nallywithnooutletforexportingthefiner-grainedmaterials. TheCentralValleyisalargestructuraltroughfilledwith Thisareaofpredominatelyfine-grainedtextureisassociatedsedimentsofJurassictoHoloceneage,asmuchas3mileswiththelargestamountofsubsidenceattributedtogroundwa-deepintheSanJoaquinValley,whichcomprisesthesouthern terwithdrawalsrecordedinthevalley.two-thirdsoftheCentralValley,andasmuchas6milesdeepintheSacramentoValley,comprisingthenorthernone-third.Mostofthefreshwater,however,iscontainedintheupperpartHydrologic System Modelingofthesedimentsconsistingofpost-Eocenecontinentalrocks ThecomplexhydrologicsystemoftheCentralValleyanddeposits(Williamsonandothers,1989),withthicknesses issimulatedusinganumberofadvancedcomponentsoftherangingfrom1,000to3,000feet.Aquifer-systemsediments USGSsnumericalmodelingcodeMODFLOW-2000(MF2K).compriseheterogeneousmixturesofunconsolidatedtosemi-TheFarmProcess(FMP)forMF2Kisusedtosimulatetheconsolidatedgravel,sand,silt,andclay. groundwaterandsurface-watercomponentsofthehydrologic Inordertobettercharacterizetheaquifer-systemdepos-cycleandtoassessandquantifythehydrologicconditions.its,lithologicdatafromapproximately8,500drillerslogsofTheFMPdynamicallyallocatesgroundwaterrechargeandboreholesrangingindepthfrom12to3,000ftbelowlandgroundwaterpumpageonthebasisofcropwaterdemand,surfacewerecompiledandanalyzedtodevelopa3-Dtexturesurface-waterdeliveries,anddepthtothewatertable.Thismodel.Thelithologicdescriptionsonthelogsweresimpli- approachisparticularlyusefulintheCentralValleywherefiedintoabinaryclassificationofcoarse-orfine-grained.privategroundwaterpumpingforirrigationisnotmetered.Thepercentageofcoarse-grainedsediment,ortexture,thenTheFMPsimulatesun-meteredhistoricalpumpageandwascomputedfromthisclassificationforeach50-footdepth thedeliveryofsurfacewaterfor21water-balanceregionsintervalofthedrillerslogs.A3-Dtexturemodelwasdevel-withintheCentralValleyforwateryears19622003.Thefarmopedforthebasin-filldepositsofthevalleybyinterpolatingdeliveryrequirement(irrigationrequirement)iscalculatedthepercentageofcoarse-graineddepositsontoa1-milespatialfromconsumptiveuse,effectiveprecipitation,groundwatergridat50-footdepthintervalsfromlandsurfaceto2,800feetuptakebyplants,andon-farmefficiency.TheFMPlinkswithbelowlandsurface.anumberofexistingMF2KPackages.TheStreamflowRout- Theresulting3-Dtexturemodelshowssubstantial ingPackage(SFR1)islinkedtofacilitatethesimulatedcon-heterogeneityandsystematicvariationinthetextureofthe veyanceofsurface-waterdeliveries.Ifsurface-waterdeliveriessediments.Theseresultscorrelatewellwithdepositionaldonotmeetthefarmdeliveryrequirement,theFMPinvokessourceareas,independentlymappedgeomorphicprovinces, simulatedgroundwaterpumpingtomeetthedemand.Basedandfactorsaffectingthedevelopmentofalluvialfans.In onthisdemand,theFMPusesspecifiedirrigationefficien-general,theSacramentoValleypredominantlyisfine-grained ciestocalculateirrigationreturnflow.AlthoughtheFMPcanandreflectsthemorefine-grainedvolcanic-derivedsediments. accountforvariouseconomicandothermanagementcriteria,However,somerelativelycoarse-graineddepositsdooccurthesecriteriawerenotsimulatedinthismodel.alongtheriverchannelsandthealluvialfansemanatingfromUtilizingMODFLOWandtheFMP,theCVHMsimu-theCascadeRangeandthenorthernSierraNevada.latesgroundwaterandsurface-waterflow,irrigatedagricul- IntheSanJoaquinValley,especiallyontheeasternside,ture,landsubsidence,andotherkeyprocessesintheCentraltheareasofcoarse-grainedtexturearemorewidespreadthan Valleyonamonthlybasis.Thismodelwasdevelopedatscalestheareasoffine-grainedtextureandoccuralongthemajorriv-relevanttowatermanagementdecisionsfortheentireCentralers.InthesouthernpartoftheSanJoaquinValley,thealluvialValleyaquifersystem,whichwasdiscretizedhorizontallyintofansderivedfromtheglaciatedpartsoftheSierraNevada 20,000 model cells of 1-mi2arealextent,andverticallyintoaremuchcoarsergrainedthanthealluvialfanstothenorth.10layersranginginthicknessfrom50to1,800ft.ThetextureIncontrasttotheeasternSanJoaquinValley,thewesternSan modelwasusedtoestimatehydraulicconductivityforeveryJoaquinValleygenerallyisfiner-grainedandisunderlainbycellinthemodel.Landsubsidence,animportantconsequencetheCorcoranClayMemberoftheTulareFormation(hereafterofintensegroundwaterpumpageinsusceptibleaquifersys-referredtoastheCorcoranClay).Thesefinertexturesreflecttems,especiallyintheSanJoaquinValley,issimulatedusingthesourcematerial:shalesandmarinedepositsoftheCoast theSUBPackage.Intra-boreholeflow,animportantmecha-Range.Theserocksgenerallyyieldfiner-grainedsediments nismforverticalflowwithinandbetweenhydrogeologicunitsthanthegraniticparentrocksthatmakeupthealluvialfansinpartsofthevalley,issimulatedacrosstheCorcoranClayontheeasternsideofthevalley.Inaddition,thisfiner-grained usingtheMNWPackage.texturemayberelatedtothefactthatthewesternsideofthe 21. Introduction 3Thehydrologyofthepresent-dayCentralValleyandtemporalinputdataforthemodeltobeupdatedmoreeffi-theCVHMmodelaredrivenbysurface-waterdeliveriesandciently.Thiscapability,inturn,facilitatesusingthemodelassociatedgroundwaterpumpage,whichinturnreflectspatialwithclimatedataderivedfromGCMs.Theinputdataforandtemporalvariabilityinclimate,wateravailability,landthecrop-basedwaterbudgetareconsistentwithoutputdatause,andthewater-deliverysystem.Ingeneral,theSacramento fromtheGCMs.ThisfacilitatesusingCVHMtoforecastValleyreceivesmoreprecipitationthanthedrier,moreheav- thepotentialsupplyofsurface-waterdeliveries,demandforilypumpedSanJoaquinValley.Thesurface-waterdeliverygroundwaterpumpage,andchangesingroundwaterstorageinsystemdevelopedforthevalleyredistributesasignificanttheCentralValley.partofthiswaterfromnorthtosouth.ThesimulatedmonthlyInthefuture,withtheaidofGIStools,theCVHMwaterbudgetsindicatethatprecipitationandsurface-wateralso could be used as a platform to connect the simulationdeliveriessupplymostofthewaterconsumedintheinitialofhydrologicprocesseswithwaterallocation/optimizationpartofthegrowingseason,whereasincreasedgroundwatermodels(forexample,CALSIM).TheCVHMcouldbeusedtopumpageaugmentsthesesupplieslaterintheseason.Gener- evaluatesub-regionalissuessuchasproposedexportationofally,themodelshowsthatduringwetyearswateristakenintowaterfromtheSacramentoValleytoSouthernCalifornia,orgroundwaterstorageintheaquifersystem,andduringdrytherestorationofsalmonhabitatintheSanJoaquinRiver.Theyearswaterisreleasedfromgroundwaterstorage.Evenduringrelativelydetaileddatabaseontexturepropertiescoupledwithdryyears,however,themodelshowsthatsomerechargetowater-levelaltitudesmaymakeCVHMparticularlyusefulforthegroundwatersystemoccursduringwinterorearlyspringassessingartificialrechargesites.Thesetypesofsub-regionalprecipitation.issuescouldbeevaluatedusingsub-regionalmodelsdynami-Duringrecentdecades,changesinthesurface-watercallylinkedtotheregionalCVHMthroughtheembedded-deliverysystemhavehadprofoundeffectsonthehydro- modeltechnologyofthelocalgridrefinement(LGR)logicsystem.BecauseoftheabundanceofsurfacewatercapabilitywithinMODFLOW.andsmalleramountsofpumpage,theSacramentoValleyandSacramentoSanJoaquinDeltagenerallyhaveexperi-encedrelativelylittlegroundwaterstoragedepletion.TheSan IntroductionJoaquinValleyhasexperiencedlargechangesingroundwaterstorage.Intheearly1960s,groundwaterpumpageexceededFormorethan50years,CaliforniasCentralValleyhassurface-waterdeliveriesintheSanJoaquinValley,causingbeenoneofthemostproductiveagriculturalregionsofthewaterlevelstodeclinetohistoriclowsonthewestsideofthe world,whichisdueinlargeparttoanamplesupplyofirriga-SanJoaquinValley,whichresultedinlargeamountsofsubsid-tionwater.Usingfewerthan1percentofU.S.farmland,theence.Inthelate1960s,thesurface-waterdeliverysystem CentralValleysupplies8percentofU.S.agriculturaloutputbegantoroutewaterfromthewetterSacramentoValleytothe(byvalue)(GreatValleyCenter,1999)andproducesonequar-drier,moreheavilypumpedSanJoaquinValley.Thesurface- teroftheNationsfood(GreatValleyCenter,1998),includingwaterdeliverysystemwasfullyfunctionalbytheearly1970s, 40percentoftheNationsfruits,nuts,andothertablefoodsresultinginwater-levelrecoveryinthenorthernandwestern(Bertoldi,1989).In2002,250differentcropsweregrown,partsoftheSanJoaquinValley.Overall,theTulareBasinpartwithanestimatedvalueof$17billionperyear(GreatValleyoftheSanJoaquinValleystillisshowingdramaticdeclinesinCenter,2005).Thepredominatecroptypesarecerealgrains,groundwaterlevelsandaccompanyingincreaseddepletionof hay,cotton,freshandprocessingtomatoes,vegetables,citrus,groundwaterstorage. treefruits,nuts,tablegrapes,andwinegrapes.ClimatevariabilityhashadprofoundeffectsontheCen-Paradoxically,mostoftheareaisaridtosemiaridandtralValleyhydrologicsystem.Forexample,thedroughtsofnaturallyiswater-deficient(Bertoldi,1989).Agriculturehas197677and198792ledtoreducedsurface-waterdeliveriesbeensustainedbythedevelopmentofanextensivesystemofandincreasedgroundwaterpumpage,therebyreversingthe reservoirsandcanalsandalsobytheavailabilityofground-overalltrendofgroundwater-levelrecoveryandre-initiatingwater.Approximately75percentoftheirrigatedlandinlandsubsidenceintheSanJoaquinValley.Sincethemid- Californiaand17percentoftheNationsirrigatedlandisin1990s,althoughannualsurface-waterdeliveriesgenerallytheCentralValley(BureauofReclamation,1994).Inaddi-haveexceededgroundwaterpumpage,waterstillisbeingtion,about20percentoftheNationsgroundwaterdemandisremovedfromstorageinmostyearsintheTulareBasin.OthersuppliedfrompumpingCentralValleyaquifers,makingitthethanthelargelossinstorageintheTulareBasin,onaverage second-most-pumpedaquifersystemintheU.S.(Bureauoftherehasbeenlittleoverallchangeinstoragethroughoutthe Reclamation,1994;PlanertandWilliams,1995;Alley,2006).restoftheCentralValley. AsimpressiveasthesenumbersarefromanagriculturalTheCVHMisdesignedtobecoupledwithforecastsfrom water-useperspective,theCentralValleyisrapidlybecomingGlobalClimateModels(GCMs)andtoallowforefficientanimportantareaforCaliforniasexpandingurbanpopulation.updatesusingremotelysenseddata.ImplementationoftheBetween1970and2000,thepopulationintheCentralVal-FMPusingGIStoolsfacilitatestheuseofremotelysensed leydoubled,reaching6.5millionpeoplein2005(Californiaevapotranspirationdata.Thetoolsallowforthespatialand DepartmentofFinance,2007)andfuturegrowthisprojectedto continue. 22. 4 Groundwater Availability of the Central Valley Aquifer, CaliforniaBecausetheCentralValleycontainssomanycommuni-(3-D),finite-differencenumericalmodeloftheCentralVal-ties, industries, and ecosystems that depend directly or indi-leyregionalgroundwater-flowsystem.Thismodelisusedtorectlyongroundwater,andbecausecompetitionforavailable evaluatethegroundwateravailabilitydescribedinChapter B.waterisintensifying,thereisaneedtoquantifytheregionsRelativetothepreviouslydevelopedCentralValleyRegionalwaterresourcesandthetrendsaffectingthemsothatpotentialAquiferSystemAnalysis(CV-RASA)model(Williamsonandfuturewater-useconflictscanbereducedoravoided.Although others,1989),thecurrentmodelwasextendedtoincorporatetheCentralValleyliesentirelywithintheStateofCalifor- aslightlylargergeographicarea(fig. A1),hasafinerspatialnia (fig. A1),itslonghistoryofgroundwaterdevelopmenttoandtemporaldiscretization,usesamore-detaileddepictionsupportagriculture,andthecomplexityandimmensityofthe ofsubsurfacegeology,andsimulatesmonthlywaterbudgetslocal,StateandNationaleconomicfactorsrelatedtotheavail-forApril1961throughSeptember2003.Finally,anappendixabilityoftheValleysgroundwater,underscoretheNational documentsmodificationstoMODFLOW-2000(MF2K)thatimportanceofthisvitalresource.Inresponse,theU.S. wererequiredtoalignthefunctionalityofMF2KwiththeGeologicalSurvey(USGS)isassessingtheavailabilityofthelandscape,hydrologicandgeologicarchitectureoftheCentralCentralValleyswaterresources,particularlyitsgroundwater.Valley.TheavailabilityandsustainabilityofgroundwaterasaInsupportoftheassessmentofgroundwateravailabilitysource of supply is a function of many factorsboth natu- intheCentralValley,thestudyhasthreeobjectives:ral and humanthat control its use. Natural factors include 1.Developabetterunderstandingofthe3-Dinternalthequantityandqualityofwater,climate,andenvironment. architectureofthefreshwater-bearingdepositsoftheHumanfactorsincludethelaws,regulations,andeconomics CentralValley;(U.S.GeologicalSurvey,2002).WaterproblemsinCaliforniacanbecategorizedunderthreebroadheadings:(1)prob-2.Utilizeenhancedwater-budgetanalysistechniqueslemsofnaturaldistribution(bothspatialandtemporal);(2)toestimatewater-budgetcomponents(recharge,technical-hydrologicproblems;and(3)political,legal,and discharge,storage)forthegroundwaterflowsystemsocialproblems(CaliforniaDepartmentofWaterResources, inareasdominatedbyirrigatedagriculture;and2005).Althoughthethirdcategoryisreferredtoattimes,thisreportfocusesonthefirsttwocategories.Thefocusofthis3.QuantifytheCentralValleysgroundwater-flowstudyisonimprovingthefundamentalknowledgeofground-systemtoenabletheforecastingofsystemresponsewateravailabilityintheCentralValley,includingwaterfluxes tostressesfromhumanandenvironmentalstressesat(groundwaterlevelsandflowsandsurface-waterinflows, scalesrelevanttowater-managementdecisions.diversions,anddeliveries),storage,andwateruseby Thefirstobjectiveisachievedthroughthedevelopmentagricultureandotherhumanactivities.ofatexturemodel.ThistexturemodelisdocumentedintheAquifer CharacteristicssectionofChapterAofthisreport.ThesecondobjectiveisachievedthroughthedevelopmentofPurpose and Scope theFarmProcess(FMP)asanadditionalsimulationcompo-nentwithinMF2K.AU.S.GeologicalSurveyTechniquesandThepurposeofthisreportistodescribegroundwaterMethodsreportdocumentstheFarmProcess(Schmidandoth-availabilityintheCentralValley.Thedescriptionsarederiveders,2006).TheapplicationoftheFMPwithinthecontextoflargelyfromthestudyresults,includingmodeling;however,simulatingtheirrigatedagricultureandasmuchaspossibleoftheyalsoutilizetheextensiveliteratureonCaliforniasCentralthehydrologiccycleintheCentralValleyalsoisdocumentedValley.Thereportcomprisesthreechaptersandanappendix.in Chapter C.ThefinalobjectiveisaccomplishedusingaChapterA(thischapter)summarizesthestudyspurposeandquantitativenumericalmodelingtool,referredtointhisreportscopeandprovidesanoverviewofthehydrogeologyoftheastheCentralValleyHydrologicModel(CVHM).CVHMstudyarea.Thehydrogeologicdescriptionincludesthegeo-consistsofalinkedlandscape-processandgroundwater-flowlogicframeworkandregionalgroundwater-flow.Chapter Bmodel that is described in Chapter C. Chapter B describes thedescribesananalysisandassessmentofgroundwateravail-applicationofthismodelforananalysisofgroundwateravail-abilityintheCentralValleytheprincipalfocusofthisabilityintheCentralValley.report. Included in Chapter B are descriptions of the effects ofdevelopmentontheflowsystem,groundwatersustainabilityandmanagement,andmonitoringofthegroundwatersystem.Chapter Cdocumentsthedevelopmentofathree-dimensional 23. Introduction 5 124 123122 121120 119Ca ReddingscKladameRC A L athRed Bluff anMtge40SacrsI F O SacramentoR ame N SanISutterFranciscoAButtesntoCentralValley Co39Pacifi Riv c OceanVaeraslle tSacramentoSi Davisy NE CA VA er LIDPaFO AciRNra C a rq u i n e z IAfi S t ra i t sStockton38 Stockton Fault c N eS a n Fra n c i s c o Sa Sav Bayn a nModesto a Jo a dEXPLANATIONJoquiGeomorphic provinceaqn BasinivuR San37Delta er in Dissected uplands JoV Sacramento River flood plainsFresno Raq a Sutter Buttesllui arn eRive n Younger fan deposits Visalia Ba y gsis Ki n g n Historical lakeseAs Extent of Corcoran Clay Selected faults Kettleman36 OAA Hills ce Line of section (figure A11)Tulare an Extent of San Joaquin BasinTulareLake bed fluvial fansABasin Major streams and selected canalsDavis Population centers0 100 200 Miles Bakersfield35 0100 200 Kilometers tsMTe h a c h a p iShaded relief derived from U.S. Geological Survey National Elevation Dataset, 2006.Albers Equal Area Conic ProjectionFigure A1. Central Valley major geomorphic provinces (modified from Davis and others, 1959; Olmstead and Davis, 1961; andJennings,1977), alluvial fans of the San Joaquin Basin (Weissmann and others, 2005), and extent and thickness of Corcoran Clay(modified from Page,1986 and Burow and others, 2004). 24. 6 Groundwater Availability of the Central Valley Aquifer, CaliforniaMethods of Analyses beconsideredamajortaskonitsown.Forexample,thestepsforcompiling,analyzing,andbuildingthewater-leveldataAssessmentofgroundwaterresourcesisanevolvingpro- necessaryforinputdatasetsandobservationsissummarizedcess.Thetechnology,availabledata,groundwaterusage,spa- in figure A4.Amoredetaileddescriptionofthedevelopment,tialdistributionofdemand,andissuesofconcernallchangecompilation, and analysis of information for the hydraulicovertime(Reilly,2005).Animprovedunderstandingofthe properties database is described in the Textural Analysisgroundwater-flowsystemcanbedevelopedasmoredataaresection of this chapter.collectedandanalyticaltoolsbecomeavailable.Theseanalyti- ThegeospatialdatabaseandGIStechniqueswerecaltoolsincludeimprovedcomputersimulationtechniques, extremelyvaluabletotheCVHM,byfacilitatingthetransfor-aswellasimproveddata-integrationanddata-management mation(includingmathematicalfunctionsorlogicalopera-practices.InordertounderstandthestatusoftheCentralVal-tions),reformatting,andintegrationofdatausedintheCVHMleygroundwatersystem,basicinformationonthegeologic(figs. A2 and A3).ThelinkbetweentheCVHMandtheGISframework,boundaryconditions,hydraulichead(waterlevel) alsorequireddevelopmentofcomputerprogramsfortranslat-distribution,waterquality,andthetransmissionandstorageinginputandoutputdata.WiththeGISandtranslationpro-propertiesoftheaquifersystemmustbeknownorestimated. grams,informationfromthedisparatedatasetswascombined,Humanactivities,suchasirrigationamountsandwaterwith-processed, and (or) re-sampled to produce spatial and temporaldrawals,alsomustbeaccountedforinthecalculationofwater datasetsneededfortheCVHMinputorobservations.Uti-availability(Reilly,2005). lizingGIS,theCVHMresultswerevisualizedspatiallyandTheevaluationofCentralValleywaterresourcesincluded temporallyalongwiththeobservationdata(fig. A2).thecollection,integrationandmanagementofnewandexist-ingdata,andthedevelopmentandcalibrationoftheCVHM.TheCVHMisusedtohelpquantifythegroundwateravailabil-Numerical Modelity. The results, conclusions, and limitations discussed in thisDevelopmentoftheCVHMresultedinacomprehensivereportarebasedonanalysesofthedataandtheCVHM.synthesisofthehydrologicdataandthecapabilitytoanalyzetheresponseofthehydrologicsystemtochangesinstress.TheCVHMprovidesaquantitativeframeworkthatcanbeusedasData Compilationatooltohelpmanagewaterresources.SixmajorclassesofdatawerecollectedorcompiledasGiventhelargeincreaseinavailabledataandmajorpartofthisinvestigation:(1)boreholelithologicdataregard-improvementsinsimulationtools,theCV-RASAmodel(Wil-ingsedimentcharacteristics;(2)hydrologicdataconsisting liamsonandothers,1989)wasupdatedusingtheU.S.Geolog-ofprecipitationrecords,historicalwaterlevelsinwells,andicalSurveysmodularmodelingsoftware,MF2K(Harbaughstreamflows;(3)compactiondatarelatedtosubsidence;(4)andothers,2000;Hillandothers,2000).Theincorporationwater-usedatafrompreviousstudies;(5)spatialland-use oftheFarmProcess(FMP)(Schmidandothers,2006)wasdata,includingcroptype;and(6)surface-waterdeliveriesand integraltomodelingthewaterbudgetcomponents.Likewise,diversions.Inaddition,informationfromothermodelingstud- incorporationofnewmodules,suchasthemulti-nodewelliesoftheCentralValleywasreviewed,analyzed,andcom-(MNW)(HalfordandHanson,2002),subsidence(SUB)piled.Inparticular,thepreviousCV-RASAmodel(William-(Hoffmannandothers,2003),andstreamflowrouting(SFR1)sonandothers,1989)andthecurrentCentralValleymodeling (Prudicandothers,2004)packages,aidedinmorerealisticeffortbytheCA-DWR(C.Brush,CaliforniaDepartmentof simulationofthesystem.ThedevelopmentandcalibrationofWaterResources,writtencommun.,February21,2007)weretheCVHMisdocumentedindetailinChapter C of this report.used.ThesedatawereincorporatedintotheCVHM.DetailsTheCVHMincludessimulationofgroundwater-flowregardingthedataaredescribedinChapter C of this report. in a sand-silt-clay aquifer system. The system has beenAnoverviewofthedatatypesanddata-integrationand subjecttogroundwaterwithdrawals,landsubsidence,anddata-managementtechniquesfollows. rechargebybothnaturalprocessesandexcessirrigationwater.Duringthepastdecade,GeographicInformationSystems CVHMincorporatesadynamicallyintegratedwatersupply-(GIS)haveadvancedconsiderablyastoolsforstoring,analyz- and-demandaccountingsystematmonthlytimescalesforing,manipulating,displaying,andmodelingsurface-waterand bothagriculturalareasandareasofnativevegetation.Thegroundwaterdata.GIStoolsalsoareusefulforlinkingspatial CVHMprovidesforamoreaccuratesimulationofirrigatedandtemporaldatatomodelinputandoutput.Whendevelop-agriculture,surface-water,andgroundwater-flowacrosstheinga3-DnumericalhydrologicmodelofaheterogeneousentireCentralValleysystemthanthepreviousCV-RASAaquifersystemhavingcomplexsurface-watermanagement model.Analysesofthetransienteffectsofvariabilityinprocesses,suchastheCentralValley,compilationofacom-surface-waterdeliveriesandassociatedgroundwaterpumpageplexarrayofdifferentcategoriesandtypesofdataisrequired arepresentedforthreespecificclimaticconditions:drought,(figs. A2 and A3).Developingevenoneofthesedatatypescan wet,andtypicalyearconditions. 25. Introduction 7DATAGroundwater Levels Centralized and Flows TextureFlow ModelModel GeospatialCVHMDatabase Hydrogeologic PropertiesV I S U A L I Z AT I O NFigure A2. The relation and flow of information used in analyzing the Central Valley Hydrogeologic system. Both interpretive andmodeling data flow in and out of the centralized geospatial database. The texture model, data in the geospatial database, and modelingresults are visualized throughout the data gathering, analysis, and modeling stages of the project.Previous InvestigationsneedsforinformationtoimprovemanagementoftheNations groundwaterresources.TheobjectiveoftheRASAprogramBecauseofthelonghistoryofgroundwaterdevelopmentwastodefinetheregionalgeohydrologyandestablishaframe-anditsimpactsintheCentralValley,therearemanyhydro- workofinformationthatcouldbeusedforregionalassess-logicinvestigationsoftheCentralValleyaquifersystem.Thementofgroundwaterresources.Twenty-fiveregionalaquiferCA-DWR,theUSGS,andvariouslocalandFederalagenciessystemswerestudiedundertheRASAprogram,includingthehaveallcompletednumerousstudies.ManyofthesestudiesCentralValley(SunandJohnston,1994).aresummarizedbyBertoldiandothers(1991).Theearli-TheCV-RASAprojectprovidedawealthofinforma-estsystematicstudiesweredonebyCaliforniasfirstStatetionontheCentralValley(Williamson,1982;DiamondandEngineer,WilliamHall,andhisstaff(Hall,1886;Hall,1889;Williamson,1983;Hull,1984;MullenandNady,1985;Page,andMendenhallandothers,1916).Bertoldi(1979)compileda1986;Williamsonandothers,1989;Bertoldiandothers1991;bibliographyofnearly600reportsongroundwaterintheCen-amongmanyothers),includingaregionalgroundwater-flowtralValley.Sincethen,anumberofsite-specificandregional model.Thegroundwater-flowmodelsimulatedconditionsgroundwatermodelshavebeencompletedbyvariousFederal,from1961to1977,aperiodoflargeandvariablestressesonState,andlocalagenciesaswellasprivateconsultants.Two thegroundwater-flowsystem,butatarelativelycoarsespatialofthesestudiesareregionalmodelingeffortsandaresumma-scale.TheCV-RASAmodelgridcellswere36mi2, and therizedbelow. freshwater-bearingdepositswererepresentedbyfourmodel layers.Theresultingmodelrepresentedflowconditionsfor largeregions,butgenerallywasinadequateatscaleslessthanRecent Regional Groundwater Models about 500 mi2.Becausewater-managementdecisionstypicallyCentral Valley Regional Aquifer-System Analysisaremadeatthescaleofindividualwaterdistricts,which(CV-RASA)often are smaller than 500 mi2,theCV-RASAmodelcannot beusedappropriatelyforprovidinginformationrelevanttoTheUSGSinitiatedtheRegionalAquifer-SystemAnaly-managementdecisionsatthosescales.sis(RASA)programin1978inresponsetoFederalandState 26. 8 Groundwater Availability of the Central Valley Aquifer, California SoilsTopographyRemote SensingSoil Surveys (STATSGO)Digital Elevation Models Satellite ImagerySoil Properties DataTopographic Maps MoDISGeology Vegetation & Land UseGeologic MapsGeologic Cross Sections CentralizedLand Use/Land Cover Maps (DWR) Agricultural DataDrillers LogsGeospatial Crop Data DatabaseOriginal Data Types ClimateGeophysicsPrecipitation Data GravityTemperature Data Seismic/EarthquakeHumidity Magnetics/Resistivity Evapotranspiration Hydrology ChemistryAnthropogenic ControlsWater Well InformationAquifer Chemistry Surface Water Delivery Aquifer TestsSpring ChemistrySurface Water Diversions Aquifer Properites SU ChemistryEnvironmental RequirementsSurface Water DataRedox ChemistryFigure A3. The diversity of data types and categories included in the centralized geospatial database. Data types in bold were usedspecifically in this study. TheCV-RASAmodelinitiallyutilizedawaterbudgetsimulatevariationsindifferentbudgetcomponentswasnotthatwasbasedonnetrechargetotheflowsystem.During veryuseful,anditwasclearthatrefinedbudgetestimatesweremodelcalibration,thenetrechargefluxeswerechangedsub- needed.SubsequenttotheCV-RASAmodel,Gronbergandstantially.Becausethesimulatedwaterbudgetwassignifi-Belitz(1992),Belitzandothers(1993),andBrushandotherscantlydifferentfromtheestimatedbudget,itwasunclear(2004)eachdevelopedanalternativeapproachtoestimatingwhetheruncertaintyinthebudgets(simulatedandestimated)thewaterbudgetbasedoncropwateruse,irrigationefficiency,wasduetoerrorsinthebudgetcomponentsortosimula- andsurface-waterdeliveriesandappliedtheapproachtopartstionerrors.Asaconsequence,useoftheCV-RASAmodeltooftheSanJoaquinValley. 27. Introduction 9DWR USGS Hydrology Water Levels Water Levels LocationsLocations Water Well InformationConstruction ConstructionAquifer TestsAquifer Properites Surface Water DataCombined Water-LevelDatabase21,417 wells873,073 water levels Overlapping records Missing information Location discrepancies Construction Measurement discrepanciesData Analysis Temporal distribution Specific time periods Climate control Continuous record Spatial distribution Water balance areas Basin to foothillsCVHMSubset 206 wells19,725 water levelsCalibration Hydrographs Observations Water levels Water-level gradients Change in water levelsFigure A4. An example of the detail for compilation, integration, and analysis for one data type (water-level nformation). 28. 10 Groundwater Availability of the Central Valley Aquifer, CaliforniaCalifornia Central Valley Groundwater-Surface-Watersouthalongthemarginofthevalley,themaximumelevationSimulation Model (C2VSIM)is about 1,700 ft. Forconvenienceofdiscussion,thevalleycanbedividedCA-DWRcurrently(2008)isusingthe3-Dfiniteele- intotwolargeparts:thenorthernone-thirdisknownasthementcodeIntegratedWaterFlowModel(CaliforniaDepart-SacramentoValleyandthesoutherntwo-thirdsisknownasthementofWaterResources,2007b)todevelopanintegratedSanJoaquinValley(fig. A1).TheSanJoaquinValleycanbegroundwater-surface-watermodelfortheCentralValley; splitfurtherintotheSanJoaquinBasinandtheTulareBasinthismodelisreferredtoasC2VSIM.C2VSIMsimulatesthe (fig. A1 and table A1).Inthisreport,thetermSanJoaquindevelopmentofthegroundwater-flowsystemandgroundwa- Valleywillbeusedtorepresentthesoutherntwo-thirdsoftheter-surfacewaterinteractionsonamonthlybasisfromOctober CentralValley,asawhole.Wheremoredetailiswarranted,the1921toSeptember2003(C.Brush,CaliforniaDepartmentofnorthernpartoftheSanJoaquinValley,theSanJoaquinBasin,WaterResources,writtencommun.,February21,2007).The willbedistinguishedfromsouthernpart,theTulareBasin.groundwater-flowsystemisrepresentedwiththreelayers,each TheSanJoaquinandSacramentoValleysmeetintheDeltahaving1,393elementsranginginsizefromabout2to65mi2.areawherethecombineddischargeoftheSacramentoandSanThemodelofthegroundwater-flowsystemiscoupledwithJoaquinRiversflowsthroughtheCentralValleysonenaturalone-dimensionalland-surface,streamflow,lake,andunsatu-outlet,theCarquinezStrait,onitswaytoSanFranciscoBayrated-zoneprocesses.Land-surfaceprocessesaresimulatedandthePacificOcean(fig. A1).JusteastoftheDelta,severalusing21subregionscorrespondingtoCA-DWRwater-supply streamsissuefromtheSierraNevadaintothevalleyandflowplanningareas.Thesurface-waternetworkissimulatedusingtotheDeltainanareareferredtoastheEastsideStreams.449streamnodesrepresenting75streamreaches,with80diversionlocationsproviding108deliveries.Thecompilationofthemonthlywaterdeliveryanddiversioninformationfor Climatethese21subregionsisasubstantialcontributiontowardunder-standingthehydrologyoftheCentralValley.ThecalibratedClimateintheCentralValleyisarid-to-semiaridhot,C2VSIMmodelwillbeusedtosimulatethegroundwater-flow Mediterranean.Precipitationduringanaverageyearrangessystem and calculate stream accretions and depletions for usefrom13to26inchesintheSacramentoValley(46inchesinCALSIM-III(CaliforniaDepartmentofWaterResources,intheextremenorthernpartofthevalley)andfrom5to2007a).CALSIM-IIIisareservoir-riverbasinsimulation18inchesintheSanJoaquinValley(fig. A5A).DramaticmodelusedforplanningandmanagementoftheStateWater deviationsfromaverageclimaticconditionsaremanifestedProjectandCentralValleyProject,whicharelargesurface- asdroughtsorfloods.MostoftheCentralValleyispronetowaterstorageanddistributionnetworksinCaliforniasCentral flooding.About85percentoftheprecipitationfallsduringValley(C.Brush,U.S.GeologicalSurvey,writtencommun.,NovemberthroughApril,halfofitduringDecemberthrough2006). Februaryinaverageyears(fig. A6).Thevalleyishotanddry duringthesummer,andcoolanddampinthewinter,whenthe areafrequentlyiscoveredbyagroundfogknownregionally astulefog.Referenceevapotranspiration(ETo)isrelativelyStudy Area high,andrangesfrom45inchesintheSacramentoValleyto 56inchesintheSanJoaquinValley(fig. A5B).Ingeneral,TheCentralValley,alsoknownastheGreatValleyof mostofthevalleyisinastateofperennialwaterdeficiency;California,coversabout20,000mi2 and is one of the more EToexceedsprecipitationbyasmuchas3ft.Overall,pre-notablestructuraldepressionsintheworld.Itoccupiesacen-cipitationexceedsEToduringthewintersandEToexceedstralpositioninCaliforniaboundedbytheCascadeRangeto precipitationduringthesummers.thenorth,theSierraNevadatotheeast,theTehachapiMoun-tainstothesouth,andtheCoastRangesandSanFranciscoBaytothewest,thevalleyisavastagriculturalregiondrained Sacramento ValleybytheSacramentoandSanJoaquinRivers(fig. A1).Theval-leyaveragesabout50miles(mi)inwidthandextendsabout Geographically,theSacramentoValleyisboundedonthe400minorthwestfromtheTehachapiMountainstonearRed- eastbytheSierraNevadaandonthewestbytheCoastRangeding(fig. A1).Generally,thelandsurfacehasverylowrelief.andKlamathMountains.TheonlysignificanttopographicItsconfigurationistheresultofmillionsofyearsofalluvialfeaturehere,orontheCentralValleyflooratlarge,isSut-andfluvialdepositionofsedimentsderivedfromthebordering terButtes,avolcanicremnantinthesouth-centralpartofthemountainranges.Mostofthevalleyliesclosetosealevel,but SacramentoValley(fig. A1).TheSacramentoRiver,whichisishigheralongthevalleymargins.Mostofthevalleybound-thelongestriversystemintheStateofCalifornia,flowsfromaryalongtheeasternedgeisabout500feet(ft)abovesealevel theCascadeRangeinthenorthtotheSanFranciscoBay/Sac-andmostofthewesternboundaryrangesfrom50to350ft ramentoSanJoaquinRiverDelta;majortributariesarethePitabovesealevel.Neartheapexesofsomealluvialfansinthe (northofthestudyarea),Feather,Yuba,Bear,andAmerican Rivers(fig. 5A). 29. Study Area 11Table A1.Water-balance subregions within the Central Valley, California.[Generaldescriptionbasedondepletionstudyarea(DSA)names(whereavailable)orsubareasfromWilliamsonandothers(1989;fig.A27).DSA49issubdi-videdintofoursubregionsAD,andDSA60issubdividedintoeightsubregionsAH.Routedsurfacewaterdeliveriesareconveyedalongstreamsorcanalstoawater-balancesubregion.Non-routedsurfacewaterdeliveries,orwatertransfers,aresurface-waterdeliveriestoawater-balancesubregionnotconnectedtoastreamormajorcanal.Thisconveyancetypicallyoccursthroughsmallcanalsordiversionditches.DWR,CaliforniaDepartmentofWaterResources;mi2,square mile]Routed Non-routedTotal SiteGeneralDWR DSAsurface- surface- Regionsarea identifier descriptionnumber waterwater(mi2)deliveries deliveries SacramentoValley 1SacramentoRiveraboveRedBluff(ReddingBasin)DSA58 611 2None 2RedBlufftoChicoLanding(RedBluff,Corning,DSA10 1,163 3NoneBend,Antelope,DyeCreek,LosMolinos,andVinaBasins) 3ColusaTrough(MostofColusaBasinandCapayDSA12 1,112 4NoneValleyBasin) 4ChicoLandingtoKnightsLandingproximaltothe DSA15 560 1NoneSacramentoRiver 5EasternSacramentoValleyfoothillsnearSutterButtes DSA69 957 26(NorthandSouthYuba,EastButteandeasternpartsofWestButteandSutterBasins) 6Cache-Putaharea(WesternSolanoandmostofDelta DSA65 1,044 4NoneandYoloBasins) 7EastofFeatherandSouthofYubaRivers(NorthDSA70 534 44AmericanBasin) EastsideStreams8ValleyflooreastoftheDelta(CosumnesandpartsofDSA59 1,362 6NoneSouthAmericanandEasternSanJoaquinBasins) Delta 9Delta(partsofSolano,EasternSanJoaquin,South DSA55 1,026 1NoneAmerican,andmostofTracyBasins) SanJoaquinBasin 10 Delta-MendotaBasin DSA49A1,083 1 7 11 ModestoandsouthernEasternSanJoaquinBasinDSA49B664 6None 12 TurlockBasin DSA49C540 5None 13 Merced,Chowchilla,andMaderaBasins DSA49D1,648 6 2 TulareBasin14 WestsideandNorthernPleasantValleyBasinsDSA60A1,071None 3 15 TulareLakeandWesternKingsBasin DSA60B1,423 4 5 16 NorthernKingsBasinDSA60C478 2 1 17 SouthernKingsBasinDSA60D569 2 1 18 KaweahandTuleBasinsDSA60E1,358 4 4 19 WesternKernCountyandSouthernPleasantValley DSA60F1,365 2 3Basin 20 NortheasternKernCountyBasinDSA60G705 23 21 SoutheasternKernCountyBasin(Arvin-Maricopa DSA60H1,105 32area) TOTAL 20,378 6441ThecityofSacramentoandthesurroundingcommuni- SacramentoFeatherRiversystemcreatebackwaterbasinsoftiesformthemajorpopulationcenteroftheregion.Withtheheavyclaysoilsthatsustainricefarmsandduckclubs.Truck,exceptionofRedding,citiesandtownsnorthofSacramento field,orchard,andricecropsaregrownonapproximatelyarelocatedinmainlyagriculturalareas.The1995population2.1millionacres;ricerepresentsabout23percentofthetotaloftheSacramentoValleywas2.4million(California acreage(CaliforniaDepartmentofWaterResources,2003).DepartmentofWaterResources,2003).TheSacramentoValleyhasmildwintersandhot,drysummers.Thenaturalleveesthatborderthe 30. 12Groundwater Availability of the Central Valley Aquifer, CaliforniaEXPLANATIONAverage annual inflow, in thousands of acre-feet per year ALess than 100100.1 to 500 Red Bluff500.1 to 1,0001,000.1 to 2,0002,000.1 to 3,0003,000.1 to 4,000 Feather River4,000.1 to 5,000 SacrameYubaRiverGreater than 5,000 nto R Bear RiverSelected streamsiverAmericanand riversRiverCosumnesDavis Precipitation stationRiver and identifier DavisMokelumneRiver Average annualCalaverasprecipitation, Riverin inches per yearStanislaus River6 to 8 9 to 1011 to 12 Tuolumne13 to 14 River Merced Sa15 to 16 River nJ17 to 18 oaqu19 to 20 inRiSan Joaquin ve21 to 22 rRiver23 to 2425 to 2627 to 2829 to 30 Kings31 to 32FSlo resn River33 to 34 ug ohKaweah35 to 36 River Los Gatos37 to 38 Creek Tule39 to 40 River41 to 42White43 to 44River45 to 46 Kern River 050 100 MilesBakersfield 0 50 100 KilometersShaded relief derived from U.S. Geological SurveyNational Elevation Dataset, 2006. Albers Equal Area Conic ProjectionFigure A5. A, Surface-water inflows and average annual precipitation for September 1961 through September 2003 throughout the Central Valley,California. B, Average annual reference evapotranspiration (ETo) for September 1961 through September 2003 throughout the Central Valley, California.ETo data were calculated from PRISM temperature data (Climate Source, 2006). The surface-water inflows are from U.S. Geological Survey files andCalifornia Department of Water Resources (C. Brush, written commun., February 21, 2007). Precipitation data are from Parameter-Elevation Regressionson Independent Slopes Model (PRISM) data (Climate Source, 2006). 31. Study Area13 EXPLANATIONAverage annual reference evapotranspiration,Bin inches per year45.5 to 46Red Bluff 46.1 to 4747.1 to 4848.1 to 4949.1 to 5050.1 to 5151.1 to 5252.1 to 5353.1 to 5454.1 to 5555.1 to 56Selected streams and rivers DavisPrecipitation stationDavisand identifier 050100 Miles Bakersfield 050 100 Kilometers Shaded relief derived from U.S. Geological Survey National Elevation Dataset, 2006. Albers Equal Area Conic ProjectionFigure A5. Continued. 32. 14 Groundwater Availability of the Central Valley Aquifer, California 5 4.5 4AVERAGE PRECIPITATION, IN INCHES 3.5 3 2.5 2 1.5 1 0.5 0JAN FEB MAR APRMAYJUN JUL AUGSEPOCT NOVDECMONTH EXPLANATIONMonthly average precipitation (1961 to 2003) at Red Bluff Davis BakersfieldFigure A6. Average monthly precipitation for Redding, Davis, and Bakersfield, California (Climate Source, 2006).Dependingonlocation,agricultureintheSacramento otherpartsofthestatearebeingevaluatedmorecarefully.Valleyreliesonavariablecombinationofsurfacewaterand Severalareashavepassedordinancesthatregulateorimpedegroundwater.Groundwateraccountsforlessthan30percent thesetransfers.CA-DWRstudiesindicatethataddit

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Groundwater availability of the central valley aquifer, california