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Study on file with OCFCD. The Hydraulic Study describes the analyses performed on the <br />channel, diversion structure, and local storm drain inlet systems. The level of flood protection <br />offered by FO1 has not been affected. No additional flood areas have been created by the <br />proposed structure. <br />S. Comment: The description of Element 2 (Debris Containment System) specifies what <br />happens to flows/debris up to 2 feet in depth and flows/debris above 3 feet in depth but <br />under 7 feet. Provide an explanation of what happens to floating debris and flows within <br />the range of 2-3 feet of depth. <br />Response: At no point are flows fully retained by the diversion structure. For clarification, the <br />following description of operational flow ranges is provided. <br />All flows less than 20 cubic feet per second (cfs) will be redirected into the facility by the <br />cross -channel weir to be treated via an inclined (Coanda) screen and returned to channel <br />through a transfer culvert within the off -channel diversion facility (HEC-RAS Bypass <br />Culvert). Flows exceeding 20 cfs will exceed the flow capacity of the transfer culvert and <br />begin to flood the off -channel diversion facility and pass through trash nets for floating <br />debris treatment until a point such that sufficient downstream head has been built to overtop <br />the cross channel weir. At this point, flows and floating debris will be skimmed by the resting <br />reinforced boom into the off -channel diversion facility until a channel water surface of <br />approximately 18 inches has been reached. Once a water surface of 18 inches has been <br />reached, the boom will begin to float up to a water surface of 6 feet 6 inches (approximately a <br />2-year water quality event). The boom will slum and redirect the top portion of flows for <br />floating debris into the off channel diversion facility up until this set release point has been <br />reached. After a water quality event water surface has been attained, the boom will release <br />from the downstream support while remaining fixed to the upstream support. Floating litter <br />and debris directed into the off -channel diversion facility will be retained by the trash nets. <br />Concurrently, the trash nets will collapse after a water quality event water surface has been <br />attained in order to prevent damage from the 100-year flood control event water velocities. A <br />secondary coarse bar screen has been provided at the exit of the off -channel diversion facility <br />to retain pollutants that have entered the off -channel diversion facility but have either <br />bypassed the trash nets or exceeded the trash net storage capacity during a water quality event. <br />9. Comment: Please verify maintenance frequencies described in different sections of the <br />IS/MND for consistency. <br />Response: Long term maintenance, which includes removal of accumulated debris, sediment, <br />and floatables within the diversion facility, is expected to be on a 30-day maintenance cycle, <br />after each rain event, or as required. <br />10. Comment: Please state in the IS/MND and Operations & Maintenance Plan detailing all <br />required maintenance activities, responsibilities, and the frequencies associated with all <br />three project elements. All permits including those from Regulatory Agencies should be <br />shared with the OCFCD/County before they are finalized and become part of the O&M <br />Plan. <br />205--10 <br />