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<br />COMMENTARY - SHEET 18 <br /> <br />The existing channel on this sheet is small and causes the existing floodplain to fan <br /> <br />out downstream of approximately Station 22+00 over the adjacent fields. The floodplain <br />encompasses a large area, but the depths are mostly shallow (See Sheets 19 and 20). <br />The grass-lined channel section designed for the 25-year flood is proposed to <br /> <br />continue to West 64th Avenue where it will transition to a concrete-lined section which <br /> <br />TOTAL IMPROVEMENT COSTS - SHEET 18 <br />Item <br />Channel Improvements <br />Street Improvements <br />Utility Relocation <br /> <br />outfalls into Clear Creek. Three sloping riprap drop structures necessary to maintain the <br />mild slope are proposed in the grass-lined section. If all the freeboard is assumed to be <br /> <br />absorbed for conveyance, the proposed 25-year channel has capacity just sufficient to <br />carry the 100-year runoff minus that which spills out of the channel at the upstream <br />railroad crossing (Sta. 48 + 32, Sheet 17). A maintenance access road should be <br />incorporated into the channel design upstream of 64th Avenue. <br /> <br />SUB-TOTAL <br />Contingencies (25% of Sub-Total) <br /> <br />TOTAL CONSTRUCTION COSTS <br />Right-of-Way Acquisition <br />Annual Operation and Maintenance Costs <br />Present Worth Operation and Maintenance Costs <br /> <br />The concrete-lined channel is one means of transporting Little Dry Creek <br /> <br />floodwaters to Clear Creek, following the present channel alignment and minimizing the <br />right-of-way and bridge spans required. As an alternative, it may be feasible to divert <br />floodwa ters into the gravel pit to the east of the channel before discharging into Clear <br />Creek, and this alternative should be investigated during the final design. Significant <br />savings could be realized by eliminating the two bridges at the railroad sidings required by <br />the design as shown. Due to the steep grade in the short reach of channel between 64th <br /> <br />TOTAL IMPROVEMENT COSTS <br /> <br />Avenue and Clear Creek, an energy dissipation structure will be required at the outfall to <br />control erosion. <br /> <br />The existing floodplain should be regulated and property owners who would be <br />adversely affected by the 100-year flood should be encouraged to acquire flood insurance. <br /> <br /> I <br /> I <br /> I <br /> I <br /> I <br /> I <br /> Cost I <br />$ 587,700 <br />$ 138,000 I <br />$ 41,700 <br />$ 767,400 I <br />$ 191,900 <br />$ 959,300 I <br />$ 163,700 <br />$ (4,600) I <br />$ 66,600 <br />$ 1,189,600 I <br /> I <br /> I <br /> I <br /> I <br /> I <br /> I <br /> I <br />