South East Management Area
4.1.3 Subsurface Outflow
Subsurface outflow from the South East Management Area into the OCWD Management Area was estimated using the OCWD groundwater flow model (Basin 8-1 Alternative 2017).
4.2 CHANGES IN GROUNDWATER STORAGE Changes in groundwater storage within the South East Management Area since 2015 have been positive reflecting the rising groundwater levels measured in the wells. As indicated in Section 3.2.1, groundwater levels are the same or higher in 2021 than they were in 2017. With the exception of LF-1, groundwater levels show a rising trend, indicating that recharge to the area exceeds the discharge. Well LF-1 shows a stable groundwater level trend. These trends have persisted despite multiple years of below normal precipitation. As presented in Section 4.1, groundwater pumping in the South East Management Area is relatively minor and averages only 125 acre-feet per year over the previous 10 years (2006-2015), and 90 acre-feet in the last six years (2016-2021). The groundwater level and pumping data indicate groundwater production is below the sustainable yield of the basin.
4.3 WATER YEAR TYPE
No update since the 2017 Alternative – See 2017 Alternative.
4.4 ESTIMATE OF SUSTAINABLE YIELD The sustainable yield of the South East Management Area is approximated by the volume of average annual recharge that is estimated to enter the basin (approximately 2,900 acre-ft), as shown in Table 4-1. Average annual groundwater production over the last 5 years, ranging from 0 acre-feet to 389 acre-feet and averaging approximately 90 acre-feet, is significantly below the sustainable yield, which is supported by rising groundwater levels in the area over the same time period. Due to production rate limitations and groundwater quality issues, it is unlikely groundwater production in the South East Management Area will ever increase to the sustainable yield.
4.5 CURRENT, HISTORICAL, AND PROJECTED GROUNDWATER BUDGET
IRWD does not plan any significant changes to groundwater use in the South East Management Area that would change the water budget. The historical water budget is
BASIN 8-1 ALTERNATIVE 2022 UPDATE
4-19 4 -2 Appendix F - 222
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