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I I I The Denver Highline Canal spill structure should be constructed after the ccnstruction of Caley detention, Also the spill structure should be built prior to constructing the storm sewer in Reach-E since the propo$ed system will outfall into the canal, perly, Other regular maintenance includes removal of the silt and sand deposits from manholes, inspection and repair of the sewer pipe, and cleaning out of excess deposits. I I The fourth construction priority should be construction of the 5-year storm sewer in Reach-E. This would eliminate damages up to the 5-year flood in Reach-E, 2, DETENTION (Caley and Powers Park) Since both the proposed Caley detention facility and Powers Park detention facility are located immediately upstream of residential areas, the primary operation and maintenance considerations should be focused on the safety aspects of the structure, Complete thorough inspections of the structures should be undertaken minimally once a year. Attention should be paid to the physical condition of the embankment and operational condition of the spillway and outlet, I The fifth construction priority is construction of the storm sewer ~n Reach-C, This would allow discharges from the proposed Caley facility to be made directly into the storm sewer system and will provide a collector system for problem drainage along Clarkson Street. I I The construction of the 5-year channel in Reach-B will have the lowest priority (sixth) based upon the net benefit criteria, I D. Operation and Maintenance The reservo~r area should be inspected and maintained to assure that sand, silt, and debris deposition does not decrease the design capacity of the facility, For the Caley detention facility, the frequent flooding up to the 2-year event will not occur since the Denver Highline Canal will intercept the local runoff in the upper basin. Since the reservoir area is to be excavated, some shallow ground water may be encountered. A subsurface drainage system is therefore recommended if the area is to be used for active recreation, I I I A major consideration in the design of improvements are the operation and maintenance aspect of the improvements, Maintenance of improvements is needed to assure that design conditions exist prior to flooding, so that maximum flood reduction benefits can be derived, 3, DENVER HIGHLINE CANAL SPILL STRUCTURE I I. STORM SEWERS The major benefit of any storm sewer is that most drainageway maintenance problems are eliminated up to the design capacity of the system, The most critical maintenance item in the system is the storm inlets. If the inlets are either undersized or subject to clogging, the design flood peaks cannot be intercepted and flooding can result, To minimize the possibility of the inlets clogging, curb-opening rather than grate-type inlets were sized in the study area, with additional length provided to allow for some blockage. A regular debris removal program must be included to assure the system will operate pro- Maintenance of the spill structure will consist of repairing the concrete surface cracks to prevent infiltration and soil piping, Some erosion may occur at the entrance due to transitional turbulence and may require remedial repairs, Maintenance of the access across the structure will be necessary so that the hiking and equestrian trails are accessible, I The operation and maintenance aspects of the major elements of the drainage- way improvements are as follows: I I 4, OPEN CHANNEL The open channel ~n Reach-B has been designed to minimize maintenance. Once grass-lined, the 4:1 side slopes should be very stable and the relatively flat concrete channel bottom should minimize erosion potential, However, after a major storm, the channel will be needed to be cleaned of any debris deposi- tion and remedial maintenance performed where needed, I I I -35- -36-