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<br />The discharges used for the Town of Nunn for a drainage area of 9.25 <br />square miles were 730 cubic feet per second (cfs), 1400, 1780, and <br />2850 for the 10-, 50-, 100-, and 500-year floods, respectively. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of streams in the commu- <br />nity were carried out to provide estimates of the elevations of <br />floods of the selected recurrence intervals along each stream <br />studied in the community. <br /> <br />Cross section data for Spring Creek Tributary in the Town of Nunn <br />were surveyed' by Gingery Associates, Inc., in June 1977. Locations <br />of selected cross sections used in the hydraulic analyses are shown <br />on the Flood Profiles (Exhibit 1). For stream segments for which a <br />floodway is computed (~ection 4..2), selected cross section locations <br />are also shown on the Floodway Map (Exhibit 2). <br /> <br />All culverts were also surveyed by the study contractor to obtain <br />elevation data and structural geometry. <br /> <br />Roughness coefficients (Manning "n") were estimated by field inspection. <br />The values ranged from 0.016 to 0.030 in the channel and from 0.035 <br />to 0.060 in the overbank areas. <br /> <br />The water-surface profiles for the 10-, 50-, 100-, and 500-year <br />floods along Spring Creek tributary were computed using the U.S. <br />Army Corps of Engineers' HEC-2 computer program (Reference 11), and <br />supplemented with other manual computations near the upper study <br />limits. <br /> <br />Flood profiles were drawn showing computed water-surface elevations <br />to an accuracy of 0.5 foot for floods of the selected recurrence <br />intervals (Exhibit 1). The starting water-surface elevation for <br />Spring Creek Tributary was determined by normal depth calculations <br />at a cross section outside the study area. <br /> <br />The profile for the Western Flow Path to Spring Creek Tributary was <br />developed using the elevations of Spring Creek Tributary at the <br />confluence and the elevations determined by developing a rating <br />curve at cross section L. <br /> <br />All elevations are referenced to the National Geodetic vertical <br />Datum of 1929 (NGVD). Elevation reference marks used in the study <br />are shown on the maps. <br /> <br />4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS <br /> <br />A prime purpose of the National Flood Insurance Program is to encourage <br />State and local governments to adopt sound flood plain management pro- <br />grams. Each Flood Insurance Study, therefore, includes a flood boundary <br />map designed to assist communities in developing sound flood plain <br />management measures. <br /> <br />5 <br />