2025 Urban Water Management Plan

Section 6 2025 Urban Water Management Plan Water Supply Characterization City of Pleasanton Public Draft | May 2026 6-5 EKI Environment & Water, Inc. supply yield specifically from the Yuba Accord, although supply considered under “water transfers” could potentially include those from the Yuba Accord. 6.1.2.2 Local Surface Water Runoff Along with ACWD, Zone 7 has a water right (Permit 11319 [Application 17002]) to divert flows from Arroyo Valle. Lake Del Valle, which is a SWP facility owned and operated by DWR, stores runoff from the Arroyo Valle watershed and imported surface water deliveries from the SWP. The lake also supports recreation and flood management. In late fall, DWR typically lowers the lake level in anticipation of runoff from winter storm events. Water supply in Lake Del Valle is made available to Zone 7 via the SBA through operating agreements with DWR. After accounting for permit conditions, inflows to Lake Del Valle are equally divided between Zone 7 and ACWD under their respective permits. While Zone 7’s historical average annual yield from Arroyo Valle ranges from 3,000-7,000 AFY, the most recent 10-year average (2016-2025) is 4,000 AFY. In the future, construction of the Chain of Lakes Conveyance System (discussed in Section 6.8) will allow for capturing more flow from Lake Del Valle storm releases and increase Zone 7’s yield. Modeling conducted to support Zone 7’s 2025 UWMP assumes an expected availability of 4,000 AFY in a normal year or at the beginning of a drought. Zone 7 plans to re- evaluate this assumption as more climate change downscaled information is developed and the Chain of Lakes (COLs) project progresses. 6.1.2.3 Local Storage Zone 7 has two existing local storage options, Lake Del Valle (surface storage) and the Main Basin (groundwater aquifer), and stores SWP deliveries in both. Lake Del Valle also stores runoff from the Arroyo Valle watershed. Zone 7 can store up to about 7,500 AF of its share of Arroyo Valle runoff in the lake (Zone 7, 2022) and carry-over runoff collected from one year until the end of the following year. Zone 7 relies on the operational storage capacity of 126,000 AF in the Main Basin for conjunctive management and recharges the basin with SWP water (Section 6.2). 6.1.2.4 Non-Local Storage In addition to local storage, Zone 7 currently participates in two non-local (out-of-basin) water banking programs, both in Kern County, and may enter into additional water banking agreements in the future. When Zone 7 has excess SWP available in wet years, the banking programs hold a portion of Zone 7’s allocated SWP supplies for Zone 7 to access during drought years through an exchange. Like other storage options, these groundwater banks significantly enhance system reliability, and yet, they do not provide a net contribution to Zone 7’s water supply over the long term. In fact, out-of-basin water banks result in some operational losses (“leave behind”). Also, certain conditions must exist to realize the benefit of these banks. That is, for Zone 7 to receive banked water supply, the Banks Pumping Plant (the major SWP pumping facility in the Delta) and the SBA must be operational. Low SWP Table A allocations (and generally low levels of outflow from the Delta) can limit the delivery of these banked supplies via exchange. Point of Delivery Agreements with DWR and Kern County Water Agency (a fellow SWC) allow Zone 7 to store SWP water in Semitropic Water Storage District (Semitropic) and Cawelo Water District (Cawelo). Semitropic and Cawelo are member units of Kern County Water Agency, which manages water deliveries to these agencies. In November 2020, the Zone 7 Board of Directors (Zone 7 Board) authorized amendments to the Point of Delivery Agreements to extend water delivery terms for storage in Semitropic and Cawelo through 2030 and recovery of banked water through 2035. Figure 6-1 shows Zone 7’s total storage and annual deposits and withdrawals from the two Kern County banks over time. The use of these banks successfully augmented Zone 7’s water supplies in 2021 and 2022 during the recent drought.