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FLOOD03982
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Last modified
1/25/2010 6:44:54 PM
Creation date
10/5/2006 12:15:37 AM
Metadata
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Template:
Floodplain Documents
Designation Number
391
County
Morgan
Community
Brush
Basin
South Platte
Title
Flood Insurance Study - Brush, CO, Morgan County
Date
2/1/1977
Designation Date
1/1/1995
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />hazard data required for this study. Floods having recurrence intervals <br />of 10, 50, 100, and 500 years have been selected as having special sig- <br />nificance for flood plain management and for flood insurance premium <br />rates. The analyses reported here reflect current conditions in the <br />watershed of the stream. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak <br />discharge-frequency relationships for floods of the selected recur- <br />rence intervals for the stream studied in detail. <br /> <br />The discharge-frequency data and flood peak estimates for Beaver <br />Creek were developed based on statistical analyses of recorded <br />stream flow records for comparable drainage areas in the high plains <br />area of eastern Colorado, western Kansas, and southwestern Nebraska. <br />These records are contained in the u.s. Geological Survey publi- <br />cation, "Manual for Estimating Flood Characteristics of Natural Flow <br />Streams in Colorado" (Reference 3), and are based on gaging records <br />that ranged from 11 to 15 years, which were taken at various points <br />on the rivers in the areas mentioned above. <br /> <br />This study uses the log-pearson Type III method (Reference 4) for <br />fitting a frequency curve to the gaging station data, and multiple <br />regression techniques for regionalization (transferring the results <br />to ungaged basins) . <br /> <br />Peak discharges for the 10-, 50-, 100-, and SOD-year floods for <br />Beaver Creek are shown in Figure 4. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of the stream studied in <br />detail were completed to provide estimates of the elevations of <br />floods of the selected recurrence intervals. <br /> <br />Cross sections for the backwater analysis of Beaver Creek were taken <br />from topographic maps prepared for the study (Reference 5). Loca- <br />tions of selected cross sections used in the hydraulic analyses are <br />shown on the Flood Profiles (Exhibit 1). For stream segments for <br />which a floodway is computed (Section 4.2), selected cross section <br />locations are also shown on the Flood Boundary (Exhibit 2) and <br />Floodway (Exhibit 3) Maps. <br /> <br />Roughness coefficients (Manning's "nil) used in these computations <br />were selected based on field inspection of the actual flood plain <br />conditions. The roughness factors were 0.035 for the channel, 0.030 <br />for the undeveloped overbank, and 0.050 for the developed overbank. <br /> <br />Water-surface profiles showing elevations of the 10-, 50-, 100-, and <br />SOa-year floods were developed using the u.s. Army Corps of Engineers' <br />HEC-2 step-backwater computer program (Reference 6). <br /> <br />8 <br />
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