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I I I I I I I I I I I I I I I I I I I I COMMENTARY - SHEET 22 An enlarged concrete-lined channel, designed for the 100-year storm is to convey flow from near station 45+10 to just above West 80th Avenue. The channel will then transition to a amble 8-foot by 6-foot box culvert that crosses beneath West 80th Avenue, after which it will transition to the existing grass-lined channel that parallels the C&S Railroad tracks. This grass-lined channel presently has capacity adequate for conveyance of the 100-year storm without permitting flow velocities to approach those which would tend to erode the grass lining. Consequently no channel improvements, except for the construction of a maintenance trail alongside of the channel, are required for this grass- lined channel stretch. Access for maintenance of the channel downstream from 80th Avenue would be by the proposed trail. Upstream from 80th Avenue, maintenance access would be via the apartment or commercial parking lots. The easements acquired for construction of the storm drainage facilities should include at least 15' on top of the channel banks for maintenance access. Since the design on the Shaw Heights tributary is based on the reduced 100-year flows, the residual100-year floodplain is confined to within the improved channel's banks. Until construction of the proposed improvements are completed, however, regulation of the 100-year floodplain and acquisition of flood insurance by those property owners who would be adversely affected by the 100-year flood should be encourage and the existing 100-year floodplain needs to be regulated. The unimproved channel section should be cleared of all debris and closely monitored to detect and correct any erosional tendencies. Since the design of the channel and related structures is based on the 100-year runoff, the existing 100-year floodplain would be eliminated. Until these improvements are completed, however, regulation of the floodplain is required and the acquisition of flood insurance by those property owners who would be adversely affected by the 100-year flood should be encouraged. TOTAL IMPROVEMENT COSTS - SHEET 22 Item Cost Channel Improvements $ 165,200 Street Improvements $ 174,600 Utility Relocation $ 30,000 SUB-TOTAL $ 369,800 Contingencies (25% of Sub-Total) $ 92,500 TOTAL CONSTRUCTION COSTS $ 462,300 Right-of-Way Acquisition $ 29,000 Annual Operation and Maintenance Costs $ (2,800) Present Worth Operation and Maintenance Costs $ 40,600 TOTAL IMPROVEMENT COSTS $ 531,900