Evaluation of the Hydrologic System and Selected Water-Management Alternatives in the Owens Valley, California
By Wesley 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
Prepared in cooperation with the Inyo County and the Los Angeles
Department of Water and Power
Major Issues addressed in this report:
- Changes in the Owens Valley ground-water system, 1963-88.
- Effect of ground-water pumping on native vegetation and streamflow.
- Alternate methods of managing water resources in Owens Valley.
- Development and use of a valleywide ground-water flow model.
CONTENTS (PDF 26K)
Abstract Introduction (PDF 585K) Purpose and Scope Previous Investigations Methods of Investigation Acknowledgments Description of Study Area (PDF 1M) Physiography Geologic Setting Climate Vegetation Land and Water Use Hydrologic System (PDF 1M) Precipitation and Evapotranspiration Precipitation Evapotranspiration Surface-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 Quality Ground-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 1963-88 Evaluation 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 Pumpage Optimal Operation of Well Fields(PDF 840K) Reliability of Results Potential Changes in Operation Need for Further Studies(PDF 25K) Aquifer System Ground-Water Flow Surface-Water Flow Water Budgets Native Vegetation Water Management Summary and Conclusions(PDF 60K) Selected References (PDF 85K)
PLATES(All 3 plates PDF 5.5M)
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)
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 of the 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 stations in 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, California 10. Photographs of major surface-water features in the Owens Valley, California 11. 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, California 12, 13. Graphs showing: 12. Annual-runoff probability for the Owens Valley, California 13. Streamflow relations for selected tributary streams in the Owens Valley, California 14.-17. Maps showing: 14. Ground-water conditions in the defined aquifer system of the Owens Valley, California, spring 1984 15. Transmissivity of valley-fill deposits as determined from aquifer tests in the Owens Valley, California 16. Average horizontal hydraulic conductivity of valley-fill deposits in the Owens Valley, California 17. Location of springs, seeps, pumped or flowing wells, and approximate area of well fields in the Owens Valley, California 18. Graph showing relation between annual pumpage and annual runoff for the Owens Valley, California 19. 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, California 22. 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 both 23. Map showing simulated change in water-table altitude in the Owens Valley, California, between water years 1963 and 1984 24. Diagram and graph showing simulated ground-water flow rates near the fast-drawdown site at Independence, California 25. Schematic section across the Owens Valley near Independence, California, showing ground-water flow under different pumping conditions 26. 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 conditions 28, 29. Sections showing the simulated water table in the Owens Valley, California, for 1988 steady-state conditions with different quantities of: 28. Runoff 29. Pumpage 30. Diagram of water-management alternative 4 for the Owens Valley, California 31.-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 drought 32. Period II, representing 3 years of recovery 33. Period III, representing 3 years of wet conditions 34, 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 field 35. Maximum pumpage at each well field
1. Ground-water and vegetation study sites in the Owens Valley, California, 1982-88 2. Characteristics and purpose of ground-water flow models developed for the Owens Valley, California 3. Native plant communities in the Owens Valley, California 4. Historical periods of similar water use in the Owens Valley, California 5. Composition of native plant communities, ground-water-level and precipitation data, and range in evapotranspiration estimates at vegetation study sites in the Owens Valley, California 6. Selected surface-water gaging stations and pumped wells in the Owens Valley, California 7. Percent of long-term average annual runoff for the Owens Valley, California, water years 1935-88 8. Mean annual discharge at selected gaging stations on the Owens River-Los Angeles Aqueduct system in the Owens Valley, California 9. 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, California 11. 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, California 13. Recharge and discharge approximations for the ground-water flow model of the aquifer system of the Owens Valley, California 14. Simulated water-management alternatives for the Owens Valley, California 15. Average pumpage from well fields in the Owens Valley, California
The Owens Valley, a long, narrow valley along the east side of the Sierra Nevada in east-central California, is the main source of water for the city of Los Angeles. The city diverts most of the surface water in the valley into the Owens River-Los Angeles Aqueduct system, which transports the water more than 200 miles south to areas of distribution and use. Additionally, ground water is pumped or flows from wells to supplement the surface-water diversions to the river- aqueduct system. Pumpage from wells needed to supplement water export has increased since 1970, when a second aqueduct was put into service, and local residents have expressed concerns that the increased pumping may have a detrimental effect on the environment and the native vegetation (indigenous alkaline scrub and meadow plant communities) in the valley. Native vegetation on the valley floor depends on soil moisture derived from precipitation and from the unconfined part of a multilayered ground-water system. This report, which describes the evaluation of the hydrologic system and selected water-management alternatives, is one in a series designed to identify the effects that ground-water pumping has on native vegetation and evaluate alternative strategies to mitigate any adverse effects caused by pumping.
The hydrologic system of the Owens Valley can be conceptualized as having three parts: (1) an unsaturated zone affected by precipitation and evapotranspiration; (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-water flow model of the “aquifer system,” which is defined as the most active part of the ground-water system and which includes nearly all of the Owens Valley except for the area surrounding the Owens Lake. The model was calibrated and verified for water years 1963-88 and used to evaluate general concepts of the hydrologic system and the effects of past water-management practices. The model also was used to evaluate the likely effects of selected water-management alternatives designed to lessen the adverse effects of ground-water pumping on native vegetation.
Results of the model simulations confirm that a major change in the hydrologic system was caused by the additional export of water from the valley beginning in 1970. Average ground-water pumpage increased by a factor of five, discharge from springs decreased almost to zero, reaches of the Owens River that previously had gained water from the aquifer system began losing water, and total evapotranspiration by native plants decreased by about 35 percent.
Water-management practices as of 1988 were defined and evaluted using the model. Simulation results indicate that increased ground-water pumpage since 1985 for enhancement and mitigation projects within the Owens Valley has further stressed the aquifer system and resulted in declines of the water table and reduced evapotranspiration. Most of the water-table declines are beneath the western alluvial fans and in the immediate vicinity of production wells. The water-table altitude beneath the valley floor has remained relatively constant over time because of hydrologic buffers, such as evapotranspiration, springs, and permanent surface-water features. These buffers adjust the quantity of water exchanged with the aquifer system and effectively minimize variations in water-table altitude. The widespread presence of hydrologic buffers is the primary reason the water-table altitude beneath the valley floor has remained relatively constant since 1970 despite major changes in the type and location of ground-water discharge.
Evaluation of selected water-management alternatives indicates that long-term variations in average runoff to the Owens Valley of as much as 10 percent will not have a significant effect on the water-table altitude. However, reductions in pumpage to an average annual value of about 75,000 acre-ft/yr are needed to maintain the water table at the same altitude as observed during water year 1984. A 9-year transient simulation of dry, average, and wet conditions indicates that the aquifer system takes several years to recover from increased pumping during a drought, even when followed by average and above-average runoff and recharge. Increasing recharge from selected tributary streams by additional diversion of high flows onto the alluvial fans, increasing artificial recharge near well fields, and allocating more pumpage to the Bishop area may be useful in mitigating the adverse effects on native vegetation caused by drought and short-term increases in pumpage.
Analysis of the optimal use of the existing well fields to minimize drawdown of the water table indicates no significant lessening of adverse effects on native 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 a small area, such as the Thibaut-Sawmill well field; pumping from the upper elevations of alluvial fans, such as the Bishop well field; or pumping in an area surrounded by irrigated lands, such as the Big Pine well field. Use of these water-management techniques would provide some flexibility in management from one year to another, but would not solve the basic problem that increased ground-water pumpage causes decreases in evapotranspiration and in the biomass of native vegetation. Furthermore, the highly transmissive and narrow aquifer system will transmit the effects of pumping to other more sensitive areas of the valley within a couple of years.
Other possible changes in water management that might be useful in minimizing the short-term effects of pumping on native vegetation include sealing well perforations in the unconfined part of the aquifer system; rotating pumpage among well fields; continuing or renewing use of unlined surface-water features such as canals and ditches; developing recharge and extraction facilities in deeper volcanic deposits near Big Pine or in alluvial fan deposits along the east side of the valley; installing additional wells along the west side of the Owens Lake; and conjunctively using other ground-water basins between the Owens Valley and Los Angeles to store exported water for subsequent extraction and use during droughts.
For additional information Copies of this report can be write to: purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Information Service Placer Hall, Suite 2012 Box 25286 6000 J Street Federal Center Sacramento, CA 95819 Denver, CO 80225
Water Resources of California URL:http://ca.water.usgs.gov/rep/wsp2370/
Last Modified Tues Oct 24, 2000