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

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Santa Ana 2020 Urban Water Management Plan arcadis.com 7-10 Table 7-3: Retail: Single Dry Year Supply and Demand Comparison DWR Submittal Table 7-3 Retail: Single Dry Year Supply and Demand Comparison 2025 2030 2035 2040 2045 Supply totals (AF) 35,915 36,459 36,178 35,868 35,857 Demand totals (AF) 35,915 36,459 36,178 35,868 35,857 Difference (AF) 0 0 0 0 0 NOTES: It is conservatively assumed that a single dry year demand is 6% greater than each respective year's normally projected total water demand. Groundwater is sustainably managed through the BPP and robust management measures (Section 6.3.4 and Appendix G), direct and indirect recycled water uses provides additional local supply (Section 6.6), and based on MET’s UWMP, imported water is available to close any potable water supply gap that local sources cannot meet (Section 7.5.1). 7.3.3 Multiple Dry Year Reliability Assessing the reliability to meet demand for five consecutive dry years is a new requirement for the 2020 UWMP, as compared to the previous requirement of assessing three or more consecutive dry years. Multiple dry years are defined as five or more consecutive dry years with minimal rainfall within a period of average precipitation. The water demand forecasting model developed for the Demand Forecast TM (described in Section 4.3) isolated the impacts that weather and future climate can have on water demand through the use of a statistical model. The impacts of hot/dry weather condition are reflected as a percentage increase in water demands from the normal year condition (average of FY 2017-18 and FY 2018-19). For a single dry year condition (FY 2013-14), the model projects a six percent increase in demand for the OC Basin area where the City’s service area is located (CDM Smith, 2021). It is conservatively assumed that a five consecutive dry year scenario is a repeat of the single dry year over five consecutive years. Even with a conservative demand increase of 6% each year for five consecutive years, the City is capable of meeting all customers’ demands from 2025 through 2045 (Table 7-4), with significant reserves held by MET and conservation. For simplicity, the table shows supply to balance the modeled demand in the table. However, based on the purchase agreement the City has with MET (Section 6.2), the City is contractually able to purchase more water from MET, should the need arise.