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3.0 Flood Staee <br />In order to evaluate the need for a flood protection berm to isolate the fan installation from <br />flooding of the neazby ephemeral drainage, flood stage calculations were completed utilizing the <br />SEDCAD+ computer model. Peak discharge for the contributing drainage basin above a point <br />adjacent to the fan installation was determined for the 100-year, 24hour design storm. The <br />runoff curve numbers utilized in the design alculations reflects undisturbed conditions for the <br />up-gradient drainage basin. <br />Runoff Volume and Peak Discharge Flow <br />Hydrologic inputs and results are shown on the SEDCAD+ computer printout '~ <br />Runoff volume: 7.43 acre-ft <br />Peak Discharge: 75.09 cfs <br />Flood Staee <br />Hydrologic inputs reflex [he existing natural channel and flood-plain configurations with a five <br />foot wide channel bottom, approximately 4H:1V sideslopes, a [wenty foot wide channel sligh[ly <br />less than two feet deep, and a poorly defined flood plain (at this location) beyond the limi[s of <br />the natural channel. Channel design calculations, as shown on the computer printout, indiate <br />a depth of flow for the peak discharge from the 100-year, 24hour storm event of only 0.94 fee[. <br />• Flood flows would be contained within the existing channel and would only extend <br />approximately six feet outward from the center of the channel. A buffer of approximately 15-20 <br />feet would remain between the flood crest and the fan installation, and the existing channel <br />would provide approximately one foot of freeboard for the design flood. <br />\~'~ <br />CLVePIR1iMP <br />„ron„yA Revised • November 1993 <br />