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<br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak discharge- <br />frequency relationships for each flooding source studied in detail <br />affecting the community. <br /> <br />Flood freqency curves for the 10-, 50-, 100-, and SOO-year recurrence <br />intervals were prepared for Holyoke at U.S. Highway 385. Several <br />methods were investigated to obtain the best possible comparison <br />for frequency-curve selection (References 5, 6, 7, and 8). A detailed <br />description of the hydrologic analysis used to prepare this study, <br />is available in the Technical Addendum to the Flood Plain Information <br />report for Frenchman Creek (Reference 9). <br /> <br />Peak discharge-drainage area relationships for Frenchman Creek, <br />North Fork Frenchman Creek, and South Fork Frenchman Creek are <br />shown in Table 2. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of flooding from the <br />sources studied were carried out to provide estimates of the eleva- <br />tions of floods of the selected recurrence intervals. <br /> <br />The water-surface elevations were computed using the COE HEC-2 <br />step-backwater computer program (Reference 10). Cross sections <br />for the backwater analysis were developed using topographic maps <br />at a scale of 1:2,400, contour interval 2 feet (Reference 11). <br /> <br />Roughness factors (Manning's On") for use in hydraulic computations <br />were assigned on the basis of field inspection of flood plain areas, <br />Frenchman Creek, North Fork Frenchman Creek, and South Fork Frenchman <br />Creek roughness factors are 0.04 for the channels and 0.05 for the <br />overbank areas. A detailed description of the hydraulic analysis <br />is included in Reference 9. <br /> <br />All elevations are referenced to the NGVD. Elevation reference <br />marks used in this study are shown on the maps, the description of <br />the marks are presented in Elevation Reference Marks (Exhibit 3). <br /> <br />4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS <br /> <br />The NFIP encourages State and local governments to adopt sound flood <br />plain management programs. Therefore, each Flood Insurance Study provides <br />100-year flood elevations and delineations of the 100- and SOO-year flood <br />plain boundaries and 100-year floodway to assist communities in developing <br />flood plain management measures. <br /> <br />7 <br />