10634. The plan shall include information, to the extent practicable, relating to the quality of existing sources of water available to the supplier over the same five-year increments as described in subdivision (a) of Section 10631, and the manner in which water quality affects water management strategies and supply reliability. 10635 (b)(2). A determination of the reliability of each source of supply under a variety of water shortage conditions. This may include a determination that a particular source of water supply is fully reliable under most, if not all, conditions. 10635 (b)(4). Considerations of the historical drought hydrology, plausible changes on projected supplies and demands under climate change conditions, anticipated regulatory changes, and other locally applicable criteria.
IRWD's supplies remain relatively unchanged between normal, single-dry and five-year drought scenarios. There is a small decrease (approximately 1%) expected in IRWD’s available supplies in single dry and multiple dry years. IRWD has found that only local surface water supplies annually captured in Irvine Lake and imported supplies delivered by Metropolitan (in the event of a declared shortage) may be affected by drought. Baker WTP is primarily served by imported Colorado River water from Metropolitan; however, additional local surface water may be available when imported supplies are limited. Local Irvine Lake surface water, when available, is utilized by IRWD to produce treated potable supplies through the Baker WTP (see Section 6), and in the near future, the Howiler WTP. IRWD owns excess connected delivery capacity to Metropolitan’s system that can be utilized as needed to make up for this small loss of local surface water to the treatment plant. In the case of a declared shortage, this local surface water supply may be limited. As described in Section 6, IRWD has multiple water sources including groundwater, imported water, recycled water and surface water. Groundwater production typically remains constant or may temporarily increase in dry year cycles, based on OCWD’s management of the basin. As for imported water, Metropolitan’s 2025 UWMP concludes that Metropolitan has sufficient supply capabilities to meet expected demands from 2030 through 2050. Metropolitan’s projections are based on a repeat of the 1977 single dry-year hydrology and the updated five consecutive dry year scenario represented by the 1988-1992 period. Recycled water production also remains constant and is considered "drought-proof" since local sewage flows remain virtually unaffected by dry years. Additionally, IRWD has developed supplemental dry year supplies through its groundwater banking programs as described in Section 6. Further description of the reliability of IRWD’s water supply sources is provided in Section 7.2. A. Recent IRWD Water Reliability Studies and Evaluations As previously described in Section 1, the Water Resources Master Plan (WRMP) is IRWD’s principal planning document. The WRMP is a comprehensive document analyzing future water resource planning and decision making for all of IRWD’s operations, including financial In addition to the WRMP, IRWD continuously works to analyze water supplies and plan for the future. This includes conducting periodic water supply reliability evaluations to analyze various planning scenarios and potential impacts to IRWD water supply reliability. The water supply
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IRWD – 2025 Urban Water Management Plan
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