Evaluation of the Hydrologic System and Selected Water-ManagementAlternatives in the Owens Valley, California

ByWesley R. Danskin(Contact author for CD)

U.S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER 2370-H
Hydrology and Soil-Water-Plant Relations in Owens Valley, California
1998

Prepared in cooperation with the Inyo County and the Los AngelesDepartment of Water and Power

PDF Versions:Download Acrobat Reader
Entire Report (PDF 8.5 MB)

Major Issues addressed in this report:

• Changes in theOwens Valley ground-water system, 1963-88.
• Effect of ground-water pumping onnative vegetation and streamflow.
• Alternate methods ofmanaging water resources in Owens Valley.
• Development and use of avalleywide ground-water flow model.

CONTENTS (PDF 26K)

AbstractIntroduction (PDF 585K)  Purpose and Scope  Previous Investigations  Methods of Investigation  AcknowledgmentsDescription of Study Area (PDF 1M)  Physiography  Geologic Setting  Climate  Vegetation  Land and Water UseHydrologic System (PDF 1M)  Precipitation and Evapotranspiration    Precipitation    EvapotranspirationSurface-Water System (PDF 1M)    Tributary Streams      Percent Valleywide Runoff      Tributary Stream Recharge    Ungaged Runoff      Mountain-Front Runoff between Tributary Streams      Runoff from Bedrock Outcrops within the Valley Fill    Owens River and the Los Angeles Aqueduct    Lower Owens River    Reservoirs and Small Lakes      Reservoirs      Small Lakes    Canals, Ditches, and Ponds      Canals and Ditches      Ponds    Owens Lake  Ground-Water System    Geometry and Boundary Conditions    Hydrogeologic Units and Subunits    Hydraulic Characteristics    Movement of Ground Water    Ground-Water Budget      Discharge from Pumped and Flowing Wells      Springs and Seeps      Underflow      Irrigation and Watering of Livestock    Ground-Water QualityGround-Water Flow Model (PDF 1M)       General Characteristics      Representation of the Aquifer System      Approximation of Recharge and Discharge      Simulation Periods      Calibration      Verification      Sensitivity Analysis      Use, Limitations, and Future Revisions      Discussion of Simulated Results, Water Years 1963-88Evaluation of Selected Water-Management Alternatives (PDF 736K)  General Water-Management Considerations  Simulation of Selected Water-Management Alternatives    Alternative 1: Continue 1988 Operations    Alternative 2: Continue 1988 Operations with Long-Term Changes in Climate    Alternative 3: Increase or Decrease Long-Term Average Pumpage    Alternative 4: Manage Periodic Variations in Runoff and PumpageOptimal Operation of Well Fields(PDF 840K)   Reliability of Results  Potential Changes in OperationNeed for Further Studies(PDF 25K)  Aquifer System  Ground-Water Flow  Surface-Water Flow  Water Budgets  Native Vegetation  Water ManagementSummary and Conclusions(PDF 60K)Selected References(PDF 85K)

PLATES

1.Hydrographs showing measured ground-water levels and simulated hydraulic heads for selected wells in the Owens Valley, California (PDF 577K)2.Maps showing hydrogeologic model zones and hydraulic parameters for each layer of the ground-water flow model in the Owens Valley, California(PDF 1M)3.Maps showing locations and average values of simulated ground-water recharge and discharge in the Owens Valley, California, for water years 1970-84
Map A (PDF 1M),Maps B & C (PDF 1M),Maps D & E (PDF 1M),Maps F & G (PDF 1M)

FIGURES

Frontispiece. (PDF) Vertically exaggerated perspective and oblique view of the Owens Valley, California, showing the dramatic difference in topographic relief between the valley and the surrounding mountains. 1.Map showing drainage areas and physiographic and cultural features of the Owens Valley and the Mono Basin, California  2.Map showing location of detailed hydrologic investigations and ground-water flow models for the Owens Valley, California, 1982-88 3.High-altitude infrared imagery showing major geologic, hydrologic, and cultural features ofthe Owens Valley, California 4.Map showing generalized surficial geology of the Owens Valley drainage basin, California  5.Typical hydrogeologic sections of the Owens Valley, California 6.Photographs of native plant communities in the Owens Valley, California 7.Map, graph, and table showing contours of mean annual precipitation, relation between recent mean annual precipitation and altitude, and data for selected precipitation stationsin the Owens Valley, California 8.Graph showing annual precipitation at Bishop and Independence, California 9.Map showing estimated average annual transpiration by native vegetation during water years 1983-87 in the Owens Valley, California10.Photographs of major surface-water features in the Owens Valley, California11.Map showing location of the Owens River-Los Angeles Aqueduct system, the lower Owens River, tributary streams, lakes, reservoirs, spillgates, major gaging stations, and selected pumped wells in the Owens Valley, California12, 13.Graphs showing:12.Annual-runoff probability for the Owens Valley, California13.Streamflow relations for selected tributary streams in the Owens Valley, California14.-17.Maps showing:14.Ground-water conditions in the defined aquifer system of the Owens Valley, California, spring 198415.Transmissivity of valley-fill deposits as determined from aquifer tests in the Owens Valley, California16.Average horizontal hydraulic conductivity of valley-fill deposits in the Owens Valley, California17.Location of springs, seeps, pumped or flowing wells, and approximate area of well fields in the Owens Valley, California18.Graph showing relation between annual pumpage and annual runoff for the Owens Valley, California19. 20.Maps showing measured and simulated potentiometric surfaces in the Owens Valley, California,spring 1984, for:19.Hydrogeologic unit 1 (upper model layer)20.Hydrogeologic unit 3 (lower model layer)21.Map and graphs showing simulated ground-water recharge and discharge during water years 1963-88 in the Owens Valley, California22.Graphs showing sensitivity of simulated hydraulic heads in the Owens Valley, California, to variations in recharge and pumpage at wells in recharge areas, near well fields, and distant from both23.Map showing simulated change in water-table altitude in the Owens Valley, California,between water years 1963 and 198424.Diagram and graph showing simulated ground-water flow rates near the fast-drawdown site at Independence, California25.Schematic section across the Owens Valley near Independence, California, showing ground-water flow under different pumping conditions26.Map showing simulated change in water-table altitude in the Owens Valley, California, between water year 1984 conditions and 1988 steady-state conditions, 27.Graph showing simulated ground-water budgets for the aquifer system of the Owens Valley, California, for water years 1963-69, water years 1970-84, and 1988 steady-state conditions28, 29.Sections showing the simulated water table in the Owens Valley, California, for 1988 steady-state conditions with different quantities of:28.Runoff29.Pumpage30.Diagram of water-management alternative 4 for the Owens Valley, California31.-33.Maps showing simulated change in water-table altitude in the Owens Valley, California, for water-management alternative 4 at the end of:31.Period I, representing 3 years of drought32.Period II, representing 3 years of recovery33.Period III, representing 3 years of wet conditions34, 35.Maps showing simulated decline in water-table altitude in the Owens Valley, California, resulting from:34.A unit increase in pumpage at each well field35.Maximum pumpage at each well field

TABLES

1.Ground-water and vegetation study sites in the Owens Valley, California, 1982-882.Characteristics and purpose of ground-water flow models developed for the Owens Valley, California3.Native plant communities in the Owens Valley, California4.Historical periods of similar water use in the Owens Valley, California5.Composition of native plant communities, ground-water-level and precipitation data, and range in evapotranspiration estimates at vegetation study sites in the Owens Valley, California6.Selected surface-water gaging stations and pumped wells in the Owens Valley, California7.Percent of long-term average annual runoff for the Owens Valley, California, water years 1935-888.Mean annual discharge at selected gaging stations on the Owens River-Los Angeles Aqueduct system in the Owens Valley, California9.Location of wells and values from aquifer tests in the Owens Valley, California (PDF 118K)10.Ground-water budget for the aquifer system of the Owens Valley, California11.Simulated ground-water budget for the aquifer system of the Owens Valley, California,water years 1963-88(PDF 277K)12.Map coordinates for the ground-water flow model of the aquifer system of the Owens Valley, California13.Recharge and discharge approximations for the ground-water flow model of the aquifer systemof the Owens Valley, California14.Simulated water-management alternatives for the Owens Valley, California15.Average pumpage from well fields in the Owens Valley, California

Abstract

The Owens Valley, a long, narrow valley along the east side of the SierraNevada in east-central California, is the main source of water for the city ofLos Angeles. The city diverts most of the surface water in the valley into theOwens River-Los Angeles Aqueduct system, which transports the water more than200 miles south to areas of distribution and use. Additionally, ground wateris pumped or flows from wells to supplement the surface-water diversions tothe river- aqueduct system. Pumpage from wells needed to supplement waterexport has increased since 1970, when a second aqueduct was put into service,and local residents have expressed concerns that the increased pumping mayhave a detrimental effect on the environment and the native vegetation(indigenous alkaline scrub and meadow plant communities) in the valley. Nativevegetation on the valley floor depends on soil moisture derived fromprecipitation and from the unconfined part of a multilayered ground-watersystem. This report, which describes the evaluation of the hydrologic systemand selected water-management alternatives, is one in a series designed toidentify the effects that ground-water pumping has on native vegetation andevaluate alternative strategies to mitigate any adverse effects caused bypumping.

The hydrologic system of the Owens Valley can be conceptualized as havingthree parts: (1) an unsaturated zone affected by precipitation andevapotranspiration; (2) a surface-water system composed of the Owens River,the Los Angeles Aqueduct, tributary streams, canals, ditches, and ponds; and(3) a saturated ground-water system contained in the valley fill.

Analysis of the hydrologic system was aided by development of a ground-waterflow model of the Òaquifer system,Ó which is defined as the most active partof the ground-water system and which includes nearly all of the Owens Valleyexcept for the area surrounding the Owens Lake. The model was calibrated andverified for water years 1963-88 and used to evaluate general concepts of thehydrologic system and the effects of past water-management practices. Themodel also was used to evaluate the likely effects of selectedwater-management alternatives designed to lessen the adverse effects ofground-water pumping on native vegetation.

Results of the model simulations confirm that a major change in the hydrologicsystem was caused by the additional export of water from the valley beginningin 1970. Average ground-water pumpage increased by a factor of five, dischargefrom springs decreased almost to zero, reaches of the Owens River thatpreviously had gained water from the aquifer system began losing water, andtotal evapotranspiration by native plants decreased by about 35 percent.

Water-management practices as of 1988 were defined and evaluted using themodel. Simulation results indicate that increased ground-water pumpage since1985 for enhancement and mitigation projects within the Owens Valley hasfurther stressed the aquifer system and resulted in declines of the watertable and reduced evapotranspiration. Most of the water-table declines arebeneath the western alluvial fans and in the immediate vicinity of productionwells. The water-table altitude beneath the valley floor has remainedrelatively constant over time because of hydrologic buffers, such asevapotranspiration, springs, and permanent surface-water features. Thesebuffers adjust the quantity of water exchanged with the aquifer system andeffectively minimize variations in water-table altitude. The widespreadpresence of hydrologic buffers is the primary reason the water-table altitudebeneath the valley floor has remained relatively constant since 1970 despitemajor changes in the type and location of ground-water discharge.

Evaluation of selected water-management alternatives indicates that long-termvariations in average runoff to the Owens Valley of as much as 10 percent willnot have a significant effect on the water-table altitude. However, reductionsin pumpage to an average annual value of about 75,000 acre-ft/yr are needed tomaintain the water table at the same altitude as observed during water year1984. A 9-year transient simulation of dry, average, and wet conditionsindicates that the aquifer system takes several years to recover fromincreased pumping during a drought, even when followed by average andabove-average runoff and recharge. Increasing recharge from selectedtributary streams by additional diversion of high flows onto the alluvialfans, increasing artificial recharge near well fields, and allocating morepumpage to the Bishop area may be useful in mitigating the adverse effects onnative vegetation caused by drought and short-term increases in pumpage.

Analysis of the optimal use of the existing well fields to minimize drawdownof the water table indicates no significant lessening of adverse effects onnative vegetation at any of the well fields at the end of a 1-year simulation.Some improvement might result from pumping from a few high-capacity wells in asmall area, such as the Thibaut-Sawmill well field; pumping from the upperelevations of alluvial fans, such as the Bishop well field; or pumping in anarea surrounded by irrigated lands, such as the Big Pine well field. Use ofthese water-management techniques would provide some flexibility in managementfrom one year to another, but would not solve the basic problem that increasedground-water pumpage causes decreases in evapotranspiration and in thebiomass of native vegetation. Furthermore, the highly transmissive and narrowaquifer system will transmit the effects of pumping to other more sensitiveareas of the valley within a couple of years.

Other possible changes in water management that might be useful in minimizingthe short-term effects of pumping on native vegetation include sealing wellperforations in the unconfined part of the aquifer system; rotating pumpageamong well fields; continuing or renewing use of unlined surface-waterfeatures such as canals and ditches; developing recharge and extractionfacilities in deeper volcanic deposits near Big Pine or in alluvial fandeposits along the east side of the valley; installing additional wells alongthe west side of the Owens Lake; and conjunctively using other ground-waterbasins between the Owens Valley and Los Angeles to store exported water forsubsequent extraction and use during droughts.

For additional information          Copies of this report can be write to:                           purchased from:District Chief                      U.S. Geological SurveyU.S. Geological Survey              Information ServicePlacer Hall, Suite 2012             Box 252866000 J Street                       Federal CenterSacramento, CA 95819                Denver, CO 80225