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<br />South Platte RI~er flood plain could change drastically If the <br />bridge area were substantially reduced by debris, especIally at <br />those roadways ha~ing high embankments. These hIgher water surface <br />elevations would flood more area than shOwn In this report and in- <br />crease ~elocl ties through the unobstructed portions of the brIdges. <br /> <br />The profllesonplates 13 and 14 show the extent to which <br />flood stages are Increased at the bridges. An apprecIable stage <br />Increase occurs on the South Platte River upstream from the Burling- <br />ton Northern railroad and U.S. HlghwaV 6. All roadways crossIng <br />the South Platte Rl~er In the study reach would be o~ertopped by the <br />1000year flood. <br /> <br />Velocities of flow - Water ~eloclties during flOOdS depend <br />upon such factors as size and shape of the cross sections, conditions <br />of the stream, and bed slope; all of these factors ~ary on differ- <br />ent streams and at different locations along the same stream. On <br />the South Platte RIver In the study reach, the channel ~elocity for <br />tt>eIOO-yearflood. in general, rangesfrorn5tolOfeetpersecond. <br />The overbank ~elocity for the 100-year flood ranges, in general, <br />from 2 to 4 feet per second. The ~eloc ity of Pewne" Creek o~erflows <br />entering the Sterling arM, In general, a~erage 2 feet per second. <br /> <br />RaTe of rise and duration of flood! nq - Rat.. of ri~.. ",,,,] <br />duration of flooding, for floods comparable to the IOO-vearor500- <br />vear flood, can ~arV o~er a wide range. A flOOd on the South Platte <br />River at S-torling would peak approximately 30 hours from the time <br />it begins to rise, This flood would have an approximate duration <br />of5d"ys. Simllarly, a flood on f'cIwne" Cr"ek would peakeboul 6 <br />hours from the time of Initial rise and would have a duration of <br />approxl....tely24 hours. <br /> <br />" <br />