reliability evaluations incorporate new facilities and projects, assess impacts to supplies, consider possible changes in demands and develop recommended planning actions to ensure IRWD’s continued water reliability. The 2025 IRWD Water Supply Reliability Study Update (2025 Study) assessed IRWD’s ability to mitigate supply shortages and enhance system resilience in response to emergency disruptions and evolving local and regional water supply conditions. The impact on IRWD’s potable water supply was evaluated using the Integrated Resources Planning Distribution System Model (IRPDSM), which applies a probabilistic Monte Carlo modeling approach, over a 38-year planning horizon (2022–2059). The following planning disruption scenarios were simulated: • Seismic-induced Delta Levee Failure that would restrict State Water Project deliveries for six years. • Seismic-induced concurrent Delta Levee and Colorado River Lower Feeder Failure that would restrict State Water Project and Colorado River water delivers for six years. • Contamination-induced Dyer Road Well Field (DRWF) Reduced Operations that would reduce DRWF capacity by 50% for five years. For each of these scenarios, water shortages at the 95 th percentile were estimated based on IRPDSM modeling results and mitigation strategies – additional conservation and additional groundwater storage - were evaluated. The DRWF Reduced Operations scenario did not lead to water shortages as imports are sufficient to meet demands under this relatively low-impact scenario. However, for the Delta Levee Failure scenario, the most likely planning scenario, the 2025 Study recommended IRWD should plan for shortages through the following mitigation measures: • Secure an additional 50,000 AF of storage for integrated operations with the Kern Fan and South Valley Projects. In May 2026, IRWD secured 25,000 AF of the additional storage. • Set a goal of banking 116,000 AF of water in the IRWD Groundwater Bank, Kern Fan Project, and South Valley Projects combined. • Develop banking well recovery capacity in the amount of 24,000 AF per year for IRWD’s use. • Participate in the Sites Reservoir as a schedulable supply. For the Delta Levee and Lower Feeder Failure scenario, the 2025 Study recommended IRWD consider, in addition to the mitigation measures for the Delta Levee Failure: • Increase banking well recovery capacity to 35,000 AF per year for IRWD’s use. • Implement Level 2 of IRWD’s Water Supply Contingency Plan. The 2025 Study concluded that IRWD’s proactive investment in a diversified water supply portfolio positions IRWD to reliably meet future demands across a wide range of disruption
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IRWD – 2025 Urban Water Management Plan
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