By Charles F. Brush, Kenneth Belitz, and Steven P. Phillips
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2004-5180 _Version 1.1
Sacramento, California 2004
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Equitable implementation of regulations restricting discharges from agricultural drains into the San Joaquin River requires a greater understanding of the influence of extreme precipitation events on the ground-water flow system. As part of a larger investigation, this study estimated ground-water recharge and ground-water pumpage, two important components of the water budget in the Grasslands drainage area in the central part of the western San Joaquin Valley, California, for the water years 1972 through 2000. These estimates will be used as inputs to a numerical simulation model of the regional ground-water flow system in the continuing investigation. Crop-acreage and surface-water delivery data were compiled for 14 water districts and 6 other areas comprising approximately 97 percent of the 600-square-mile study area. Little ground-water pumpage data exists for the study area. A climate-based approach was employed to estimate annual water-table recharge flux and ground-water pumpage for 11 water-budget areas. Ground-water pumpage was estimated from the residual irrigation demand after crop consumption of surface water. Estimated recharge flux to the water table for the entire study area averaged 0.8 ft/yr, and estimated ground-water pumpage per unit area for the entire study area averaged 0.5 ft/yr. Increased discharges from agricultural drains in the late 1990s may have been due partly to 4 years of high recharge from precipitation over the 6-year period from 1993 to 1998. Knowledge of the ratio of annual crop water demand to annual potential evapotranspiration, expressed as an aggregate crop coefficient, Kd, will facilitate estimation of annual water-budget components in future studies. Annual aggregate crop coefficients, calculated each year for the entire study area, were nearly constant at 0.59 from 1983 to 2000, and reasonably constant at 0.53 prior to 1983. The overall trend suggests continuous reductions in recharge from irrigation over time. This reduction is most likely due to gradual improvements in irrigation management. The recharge and pumpage estimates are both sensitive to the consumption-distribution ratio, and the pumpage estimate is sensitive to the cropped acreage.
Abstract
Introduction
Location of the Study Area
Hydrogeologic and Climatologic Setting
Ground-Water Pumpage
Reuse of Irrigation and Drainage Water
Previous Studies
Methodology
Data Acquisition
Climate Data
Data-Collection Areas
Crop Acreages
Water Deliveries
Surface-Water Deliveries
Ground-Water Pumpage
Reuse of Irrigation and Drain Water
Consumption-Distribution Ratio
Canal Seepage
Daily Crop Soil-Moisture Budgets
Daily Soil Surface Process Model
Daily Crop Water Demand Model
Daily Soil-Moisture Budget
Annual Water Budgets
Water-Budget Model
Supply-Based Consumptive Use in Broadview
Results and Discussion
Data Acquisition
Water-Budget Inputs
Climate-Based versus Supply-Based Consumptive Use in Broadview
Annual Water-Budget Calculations
Estimated Annual Ground-Water Pumpage
Estimated Annual Ground-Water Recharge
Comparison with Other Studies
Aggregate Crop Coefficient
Surface-Water Availability Indices
Estimation Sensitivity and Uncertainty
Limitations of this Methodology
Summary
References Cited
Appendix A. Agroclimatic Data
Appendix B. Water Deliveries and District-Level Pumpage
Appendix C. Soil-Moisture Budget Results
Appendix D. Water-Budget Results
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