2025 Urban Water Management Plan

Section 7 2025 Urban Water Management Plan Water Supply Reliability Assessment City of Pleasanton Public Draft | May 2026 7-9 EKI Environment & Water, Inc. 7.2 Reliability by Type of Year The City’s potable water supply reliability and vulnerability are directly related to seasonal and climatic shortages that impact Zone 7’s water supplies. The quantity available from different supply sources varies annually depending on hydrologic conditions. Consequently, Zone 7 reviewed historical data and developed a projected yield for each water supply source (including the Main Basin) under three conditions: (1) normal water year, (2) single dry year, and (3) five-consecutive-year drought. Each condition is defined as follows: • A normal hydrologic year represents the water supplies available under normal conditions; Zone 7 uses the median outcome at demand year 2045 based on the index sequential method modeling; • A single dry year represents the lowest available water supply, which was chosen to be the driest year in the historical record, 1977; and • A five-consecutive year drought represents the driest five-year period in the historical record. Selection of the design drought corresponds with the driest five-year sequence on record, 1987-1991. Zone 7’s water supply reliability is used to represent the City’s available supplies during the above hydrologic conditions. In its 2025 UWMP, Zone 7 provides a basis of water year data table (DWR Table 7-1) for each of its water supply sources. For simplicity, this plan leaves DWR Table 7-1 blank (Table 7-1) and summarizes Zone 7’s base year information and water supply availability in Table 7-2 and Table 7-3, respectively. Table 7-1 Basis of Water Year Data (Reliability Assessment) (DWR Table 7-1) Available Supplies if Year Type Repeats ☒ Checked box indicates quantification of available supplies is not compatible with this table and is provided elsewhere in the UWMP. Location: Table 7-2 and Table 7-3  CWC §10631 (b) Identify and quantify, to the extent practicable, the existing and planned sources of water available to the supplier over the same five-year increments described in subdivision (a), providing supporting and related information, including all of the following:  CWC §10631 (b)(1) A detailed discussion of anticipated supply availability under a normal water year, single dry year, and droughts lasting at least five years, as well as more frequent and severe periods of drought, as described in the drought risk assessment. For each source of water supply, consider any information pertinent to the reliability analysis conducted pursuant to Section 10635, including changes in supply due to climate change.  CWC §10635 (a) Every urban water supplier shall include, as part of its urban water management plan, an assessment of the reliability of its water service to its customers during normal, dry, and multiple dry water years. This water supply and demand assessment shall compare the total water supply sources available to the water supplier with the long-term total projected water use over the next 20 years, in five-year increments, for a normal water year, a single dry water year, and a drought lasting five consecutive water years. The water service reliability assessment shall be based upon the information compiled pursuant to Section 10631, including available data from state, regional, or local agency population projections within the service area of the urban water supplier.