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CM2018-080 PRADO BASIN SPILLWAY IMPROVEMENTS4 CM2018-080 City Chino Hills MEMORANDUM DATE: December 4, 2018 TO: Honorable Mayor and City Council FROM: Konradt Bartlam, City Manag RE: PRADO BASIN SPILLWAY IMPROVEMENTS At their meeting on November 27, 2018, Council inquired about the status of plans to raise the Prado Dam spillway 20 feet, which would then increase the Prado Reservoir 10 feet from elevation 556 feet to 566 feet during the 100 -year storm event. This question was raised in response to the November 20, 2018, Planning Commission finding that the proposed acquisition by the Orange County Flood Control District (OCFCD) of flowage easements conforms to the General Plan pursuant to California Government Code Section 65402(c). Prado Dam is a flood control and water conservation project that has been in operation since its completed construction date of April 1941 by the U.S. Army Corps of Engineers (Corps). The dam is located on the Santa Ana River with its dam embankment located in Riverside County and with portions of the reservoir located in both Riverside and San Bernardino Counties. Since its construction, a number of modifications to expand its capacity have been completed. The current proposal to acquire flowage easements in Chino Hills is part of the Corps' Santa Ana River Mainstem Project (SARM) which is designed to provide flood protection to the communities in Orange, Riverside, and San Bernardino Counties. SARM improvements include: 1) Construction of a 550 ft. high, 3,000 ft. long Seven Oaks Dam; 2) Raising the existing Prado Dam's embankment and spillway and constructing new outlet gates; 3) Constructing or improving over 23 miles of channel; and 4) Constructing dikes, levees, drainage basins, and underground drainage facilities. Congress authorized SARM for construction in 1986 and its implementation is ongoing. Seven Oaks Dam has been completed and approximately 95% of the reconstruction work in the river channel has been completed. The Prado Dam embankment has been raised and the outlet works have been reconstructed to convey increased flood discharges. The remaining portions, including the modifications to the Prado Dam spillway, are anticipated to be completed in 2021. Should you have any questions, please contact me or Community Development Director Joann Lombardo.