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<br />IV. DESIGN STORM DISCHARGES AND FLOODING <br /> <br />A. Discharge Computations <br />The quantity of rainfall which eventually reaches a major drainage <br />channel is dependent upon the duration and intensity of the rainfall, <br />upon the quantities of rain evaporated or intercepted by vegetation, <br />upon the soil infiltration characteristics (which are affected by the slope <br />of the land) and by the volume of local runoff retained in depressions. <br />The S.C.S. has made extensive studies and observations on storm <br /> <br />runoff from different agricultural land uses and different soil groups. <br /> <br />S.C.S. soils data and the S.C.S. runoff computation procedures as <br /> <br />modified by the Bureau of Reclamation, were used for each basin. In <br /> <br />addition to computations of the normal losses as defined by the S.C.S. <br /> <br />procedure, additional losses were extracted based upon the volume of <br /> <br />runoff which would be trapped in the large scale depressions. See Figure <br /> <br />2 for an illustration of these depressions. <br /> <br />After the runoff or "excess" precipitation is computed for each <br /> <br />basin by the S.C.S. procedure, the associated hydrograph for each basin <br />was channel routed and combined with discharges from adjacent basins to any <br />obstructions of the channel, such as the railroad embankment, and reservoir <br /> <br />I <br /> <br />I <br /> <br />routed at these points. Urban flows were routed to the ponds or east <br />to Detroit Street (Highway 59). <br /> <br />I <br />" <br /> <br />-13- <br />