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HARBOR BLVD. MIXED USE TRANSIT CORRIDOR PLAN FINAL FIR <br />CITY OF SANTA ANA <br />5. Environmental Analysis <br />HYDROLOGY AND WATER QUALITY <br />Flood Hazards <br />Designated Flood Zones <br />Much of the northern half of the project area is in Zone A, a 100 year flood zone designated by FEMA, as <br />shown in Figure 5.7 -4, Flood Hazard Zones. Areas along the west side of Harbor Boulevard from 1st Street <br />north to 5th Street are in Zone A, as are areas along both sides of Harbor Boulevard from 5th Street north to <br />Westminster Avenue. The remainder of the project area, south of the above - specified areas, is in Shaded <br />Zone X, meaning that it is protected from 100 year floods by levees (FEMA 2009a, 2009b). <br />Seismically Induced Dam Inundation <br />Approximately the west half of the City of Santa Ana is in the dam inundation area for Prado Dam, which is <br />located on the Santa Ana River 18 miles northeast of the project area. The following information and analysis <br />is from a dam inundation analysis prepared by The Planning Center I DC&E for a proposed charter school at <br />2840 West 1st Street in Santa Ana, just east of the 1st Street Bridge over the Santa Ana River (The Planning <br />Center I DC&E 2013). <br />Prado Dam is owned and operated by the Los Angeles District of the Army Corps of Engineers and was <br />completed in 1941. It provides flood control and groundwater recharge capability for Orange County. The <br />dam is on the Santa Ana River approximately two miles west of the City of Corona near the head of Santa <br />Ana Canyon. Its primary purpose is to reduce the risk of damage from floods in the metropolitan areas of <br />Orange County, and it was built after a catastrophic flood on the Santa Ana River in 1938. <br />Prado Dam is an earth filled dam with a height of 106 feet and a reservoir capacity of 217,000 acre -feet. Its <br />functioning capacity was recently increased due to the construction of the Seven Oaks Dam, which was <br />completed in 1999 and is approximately 40 miles upstream on the Santa Ana River. During a flood, Seven <br />Oaks Dam will store water destined for Prado Dam for as long as the reservoir pool at Prado Dam is rising. <br />When the flood threat at Prado Dam has passed, Seven Oaks Dam will begin to release its stored flood water <br />at a rate that does not exceed the downstream channel capacity. Working in tandem, the Prado and Seven <br />Oaks Dams provide increased protection to Orange County. <br />Flood protection improvements along the Santa Ana River are being implemented as part of the Santa Ana <br />River Mamstem Project, including improvements to Prado Dam: raising the dam height 28.4 feet; <br />constructing a new outlet works to more than triple the existing outlet capacity; raising the concrete spillway <br />20 feet; constructing levees or dikes in the basin to protect properties; and stabilizing approximately 1.5 miles <br />of bluff along the Santa Ana River downstream of the Interstate 15 bridge in the City of Norco. <br />These improvements will increase Prado Dam's current 70 year level of protection to 190 -year protection and <br />will increase the reservoir capacity from 217,000 to 362,000 acre -feet. In addition, the downstream channel <br />capacity of the Santa Ana River will be increased from 9,350 cubic feet per second (cfs) to approximately <br />30,000 cfs, further reducing the potential for flooding (CCCD 2012). All work on the Santa Ana River <br />Channel is scheduled for completion in 2014, and all work on Prado Dam is scheduled for completion by <br />2018. Completion of these projects will significantly reduce flood risks on the Santa Ana River and the <br />October 2014 Page 5.7 15 <br />