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<br />1989 SWDY <br /> <br />The 1989 Section 22 study developed hydraulic data necessary to <br />determine the effects of flood mitigation projects along the South <br />Platte River at Sterling. The information included an updated <br />existing-conditions IOOdel for the South Platte lliver and corres]Xlnding <br />floodway. The updated I1lOdel was executed using the 1988 version of <br />the Corps of Engineers Standard Step-Backwater Program HEC-2 (HEC-2 <br />program) . A discussion of the updated HEC-2 ffixlel is contained in the <br />1989 study. <br /> <br />HYDRAULIC ,AN,'u;ysrs <br /> <br />.FI1J.1 PARAMEI'ERS <br /> <br />Because the conditions of the flood plain are essentially the same <br />as they were for the 1989 study. no c111mges were made to the existing- <br />condi tions 100-year flood and floodway model. The model was then <br />executed on the FebnJary 1991 versi,cm of the HEC-2 program (1992 <br />Study) . The resulting output was compared to the output for the 1989 <br />study to determine if the newer version had any significant impact on <br />water-surface elevaticms. Comparing water surface profiles showed <br />less than a 0.1 foot difference for bet:h the without-floodway <br />conditions and the with-floodway conditionswid1. no point along the <br />floodway profile exceeding the standard 1.0-foot maxirrn.nn rise. Table <br />1 summarizes the with.. and without-floodway conditions for the 1989 <br />and 1992 studies. <br /> <br />5 <br />