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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />001018 <br /> <br />"E" - Flood Fringe Filling (I-foot f100dway): This alternative is <br />es sent i ally the same as a lternat i ve "0" except that the water surface is <br />allowed to raise 1 foot, which is the present FEMA policy. This alternative <br />would reclaim more land than alternative "0", but would require special <br />approval from Arapahoe County. In either case, the floodway must transition <br />into the floodplain at the upstream end of the project area, since the floodway <br />would impact the Cottonwood Development, which is immediately upstream. <br /> <br />"F" - Arapahoe Road Bridge Enlargement: Several increased span widths <br />were investigated for ~rapahoe Road bridge (from 50 feet to 200 feet) to deter- <br />mine the full impact of the bridge backwater. The 200-foot increased span <br />would lower the 100-year water surface for a distance of approximately 200 to <br />300 feet upstream of the bridge. This was considered to be an insignificant <br />benefit and the alternative was not considered further. <br /> <br />"G" - Arapahoe Road Bridge Replacement: This alternative required the <br />replacement of the existing bridge to span the lOa-year floodplain, approxi- <br />mately 700 to 800 feet wide. ~lso required was channelization upstream and <br />downstream of ~rapahoe Road to transition the channel and obtain the maximum <br />reduction. in flooded property. A conservative estimate for the bridge con- <br />struction alone was placed at four million dollars, and the alternative was not <br />considered further for this reason. <br /> <br />"H" Excavation to Contain Flood: There are two approaches to <br />channel i zat i on for Cherry Creek that were found to be sat is factory. One <br />approach (alternate #1) excavates a trapezoidal section outside the existing <br />main channel area (see Figure-14 for definition of terms). The excavation <br />would take place at approximately the depth in the main channel which carries <br />the 10 yaer flood, (i .e. the bankfull depth). This approach results in a <br />floodplain/f10odway width of around 800 to 900 feet. <br /> <br />The second approach (alternate #2) consists of a cross section which has a <br />larger main channel in generally the same location as the existing channel and <br />an "overbank excavation" area to accomodate larger floods. The main channel <br />cross section for this option was developed using the results of the fluvial <br /> <br />-26- <br />