OCWD Management Area
4.3 ESTIMATE OF SUSTAINABLE YIELD
Even though the groundwater basin contains an estimated 66 million acre-feet when full, OCWD operates the basin within an operating range of up to 500,000 acre-feet below full condition to protect against seawater intrusion, inelastic land subsidence, and other potential undesirable results. On a short-term basis, the basin can be operated at an even lower storage level in an emergency. OCWD manages groundwater production and recharge to maintain groundwater storage levels within the established operating range. In this sense, the basin’s sustainable yield can be defined as the volume of groundwater production that can be sustained while maintaining groundwater in storage within the operating range. Basin storage is determined on an annual basis by calculating the difference between groundwater production and recharge based on OCWD’s July 1 to June 30 water year. The sustainable yield of the basin is a function of the amount of groundwater recharge from OCWD’s managed aquifer recharge program and natural recharge as a result of precipitation and percolation of irrigation flows. The process that determines a sustainable level of pumping on an annual basis considers the basin’s operating range, basin storage conditions and the amount of available recharge water supplies. As mentioned in Section 1.2, the groundwater basin is not operated on an annual safe-yield basis. The net change in storage in any given year may be positive or negative; however, over a period of several years, the basin is maintained in an approximate balance. Amounts of total basin production and total water recharged from WY1999-2000 to 2020-21 are shown in Figure 1-4.
4.4 WATER BUDGETS
The OCWD Management Area water budget for WY2016-17 to 2020-21 is presented in Table 4- 1. Estimated water budgets for dry years, average years and wet years as well as a future projected budget are presented in the 2017 Alternative.
BASIN 8-1 ALTERNATIVE 2022 UPDATE
Water Budget 4-4
Appendix F - 113
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