Item 28 - Urban Water Management Plan and Water Shortage Contingency Plan

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Santa Ana 2020 Urban Water Management Plan arcadis.com 7-14 As explained in Section 6, the City currently relies on, and will continue to rely on, three main water sources: local groundwater, recycled water, and imported water supply from MET. The City maximizes local water groundwater supply use before the purchase of imported water. The difference between total forecasted demands and local supply projections is the demand on MET’s imported water supplies from the Colorado River, SWP, and in-region storage. Local groundwater supply for the City comes from the OC Basin and is dictated by the BPP set annually by OCWD. Therefore, the City’s DRA focuses on the assessment of imported water from MET, which will be used to close any potable water supply gap local groundwater does not fill. Water Demand Characterization Beyond local supplies, the City’s water supplies are purchased from MET, regardless of hydrologic conditions. As described in Section 6.2, MET’s supplies are from the Colorado River, SWP, and in-region storage. In their 2020 UWMP, MET’s DRA concluded that even without activating WSCP actions, MET can reliably provide water to all of their member agencies, including the City, through 2045, assuming a five-year drought from FY 2020-21 through FY 2024-25. Beyond this, MET’s DRA indicated a surplus of supplies that would be available to all of its member agencies, including the City, should the need arise. Therefore, any increase in demand that is experienced in the City's service area will be met by MET's water supplies. Based on the Demand Forecast TM, in a single dry year, demand is expected to increase by 6% above a normal year. The City’s DRA conservatively assumes a drought from FY 2020-21 through FY 2024-25 is a repeat of the single dry year over five consecutive years. The City’s demand projections were developed as part of the Demand Forecast TM, led by MWDOC. As part of the study, MWDOC first estimated total retail demands for its service area. This was based on estimated future demands using historical water use trends, future expected water use efficiency measures, additional projected land-use development, and changes in population. The City’s projected water use, linearly interpolated per the demand forecast, is presented annually for the next five years in Table 4-2. Next, MWDOC estimated the projections of local supplies derived from current and expected local supply programs from the participating agencies. Finally, the demand model calculated the difference between total forecasted demands and local supply projections. The resulting difference between total demands net of savings from conservation and local supplies is the expected regional demands on MET supply. Water Supply Characterization The City’s assumptions for its supply capabilities are discussed and presented in 5-year increments under its UWMP water reliability assessment. For the City’s DRA, these supply capabilities are further refined and presented annually for the years 2021 to 2025 by assuming a repeat of historic conditions from FY 2011-12 to FY 2015-16. For its DRA, the City assessed the reliability of supplies available from MET using historical supply availability under dry-year conditions. MET’s supply sources under the Colorado River, SWP, and in-region supply categories are individually listed and discussed in detail in MET’s UWMP. Future supply capabilities for each of these supply sources are also individually tabulated in Appendix 3 of MET’s UWMP, with consideration for plausible changes on projected supplies under climate change conditions, anticipated regulatory changes, and other factors. In addition, the City has access to supply augmentation actions through MET. MET may exercise these actions based on regional