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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 />Under existing channel conditions, storm water ponding was con- <br />sidered at one point within the basin, the Powers Park Deten- <br />tion Pond. The detention effect here is by design. The facility <br />outlet is design-optimized for the 2-year storm flood flow with <br />the overflow spillway designed to pass the IOO-year storm flood <br />hydrograph. Under design conditions, the flood waters tributary <br />to the pond will be routed through the reservoir and released <br />into the conduit which proceeds downstream beneath Berry Circle. <br />Excess inflows will pass over the spillway and down the street <br />surface of Berry Circle. Some peak flood flow reduction is <br />experienced for each storm frequency at Powers Park. Natural <br />channel storage also tends to decrease peak flood flows and <br />attenuate the flood hydrograph. This effect, however, was not <br />considered in this analysis. <br /> <br />The final storm hydrographs at each of the design points are <br />enclosed to show the effect of lagging, adding and routing each <br />of the storm hydrographs. The hydrographs are identified as <br />Figures 1, 2, 3 and 4 and are at the South Platte River, main <br />and south tributary confluences and Powers Park, respectively. <br />Figure 5, Discharge Probability Curves, shows the peak flood <br />flows for each frequency at any location along the gulch for <br />both the main stream and the south tributary. <br /> <br />111-5 <br />