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<br />k lot z ~~. ass 0 C I ate s <br /> <br />3.5.2 Diversion Storage <br /> <br />The volume of diversion storage for FEMA channels was estimated as the volume of the <br />hydro graph before diversion for those values of discharges in excess of the peak <br />discharge after diversion. For non-FEMA channels, diversion volume was estimated as <br />the difference in before':' and after-diversion hydro graphs assuming hydro graphs were <br />described by the Malcom hydro graph (see Section 3.3.4) with peak discharge determined <br />from the runoff calculations using a runoff correlation (see Section 3.5.4 below). <br /> <br />3.5.3 Mitigation of Excess Runoff Due to Development <br /> <br />The volume of runoff for FEMA channels before- and after-detention is computed as the <br />difference in the HEC-HMS hydro graphs as predicted by the HEC-HMS model with a <br />peak discharge equal to the peak discharge before and after detention is used. The volume <br />for non-FEMA channels is computed in the same manner except that the hydro graph is <br />described by the Malcolm hydro graph model (see Section 3.3.4). <br /> <br />3.5.4 Correlation Models <br /> <br />For drainage basins with correlation models (basins with non-FEMA model channels), <br />the hydro graphs before and after detention are determined by the Malcom hydro graph <br />with peak discharge determined from the correlation of runoff with area and level of <br />development (see Section 3.3.3) and runoff volume equal to the design rainfall multiplied <br />by the estimated imperviousness fraction for the land development condition being <br />evaluated. <br /> <br />3-8 <br /> <br />Klotz Associates Project No. 0127.008.000 <br />January 2009 <br /> <br />La Porte Citywide Drainage Study <br />City of La Porte <br />