Item 26 - Adoption of the City of Santa Ana Emergency Operations Plan

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City of Santa Ana Emergency Operations Plan Part I Basic Plan Orange County line. Portions of the reservoir behind the dam are in both Riverside and San Bernardino Counties. The dam is located at the upper end of the Lower Santa Ana River Canyon, which is a natural constriction controlling 2,255 square miles of the 2,450 square mile Santa Ana River watershed. Prado Dam provides flood control and water conservation storage for Orange County. It is the downstream element of the Santa Ana River flood control system. The purpose of the system is to collect runoff from the uncontrolled drainage areas upstream, along with releases from other storage facilities. Generally, when the water surface elevation in the reservoir is below 494.0 feet during flood season or 505.0 feet during non -flood season, water releases are made to provide water supply to downstream consumers. These releases are coordinated with the Orange County Water District and are based upon the capacity of their groundwater recharge facilities and agreements with other agencies. If the water level in the reservoir exceeds the top of the buffer pool (the water levels mentioned above), flood control releases commence. The objective of the flood control release is to drain the reservoir back to the top of the buffer pool as quickly as possible without exceeding the capacity of the channel downstream. In current practice, when the water surface in the reservoir exceeds the top of the buffer pool, water releases are increased to match water inflow, up to 5000 cubic feet per second (cfs). If inflows exceed 5000 cfs, the excess water accumulates in the reservoir. If the water surface elevation in the reservoir reaches 543.0 feet, uncontrolled releases from the spillway will commence. These high flows of water would result in very high, fast-moving water in the Santa Ana River through the City. These could potentially overtop the banks of the River, particularly if it occurs in conjunction with heavy rainfall, resulting in flooding conditions. In addition to the potential for overtopping, the high, fast flow could endanger pedestrians, homeless encampments, or any persons in or near the riverbed. Catastrophic failure of Prado Dam would inundate a wide swath of northern, central and coastal Orange County, from the Riverside County line to Huntington Beach and including a large portion of the City of Santa Ana. Almost I million people live within this inundation zone. Villa Park Dam — Villa Park Dam is an earthen dam on Santiago Creek approximately 5 miles upstream of the City of Santa Ana. It was constructed for flood control, primarily during rainstorms, for the Cities of Villa Park, Orange, Tustin and Santa Ana and regulates the flow of Santiago Creek into the Santa Ana River. Santiago Creek Dam - Santiago Reservoir and Dam is an earth -filled structure owned by the Serrano Water District (SWD) and Irvine Ranch Water District (IRWD). Santiago Reservoir provides raw potable water storage for SWD and IRWD. It is located on Santiago Creek about three miles upstream of Villa Park Dam in Santiago Canyon and about 8 miles upstream of the City of Santa Ana. The Dam/Reservoir Failure Annex to this Plan provides charts and maps to detail the water levels and geographic extent of the resulting flooding for these scenarios. 79