Laserfiche WebLink
<br />Except for portions of Sulphur and Tallman Gulches, cross section <br />data were obtained b field measurements. <br /> <br />All bridges, culverts, and other structures were surveyed to <br />obtain elevation data and structural geometry. <br /> <br />Locations of selected cross sections used in the hydraulic <br />analyses are shown on the Flood Profiles (Exhibit 1). For stream <br />segments for which a floodway was computed (Section 4.2), selected <br />cross section locations are also shown on the Flood Insurance Rate <br />Map lExhibit 2). <br /> <br />Roughness coefficients (Manning's On") were estimated by field <br />investigation and from pictures of the stream and its flood plain <br />using Roughness Characteristics of Natural Channels (Reference 17), <br />(Reference 17), Open-Channel Hydraulics (Reference 18), and Hand- <br />book of Applied Hydraulics (Reference 19). The "n" values for <br />Cherry Creek ranged from 0.04 to 0.055 for the channel and from <br />0.061 to 0.095 for the overbanks. For Sulphur and Tallman Gulches, <br />the "n" values ranged from 0.03 to 0.05 for the main channels and <br />from 0.03 to 0.12 for the .overbanks. <br /> <br />For Cherry Creek, the COE used critical depth to determine the <br />starting water-surface elevation. For Sulphur and Tallman <br />Gulches, the starting water-surface elevation was determined using <br />the stream slope at a starting valley cross section. <br /> <br />Calculation of normal depth from field cross section and the <br />estimation of top width was used to plot flooding for approximate- <br />study areas. <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). Elevation reference marks used in this <br />study are shown on the maps; the description of the marks are <br />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 <br />provides 100-year flood elevations and delineations of the 100- and 500- <br />year flood plain boundaries and 100-year floodway to assist communities <br />in developing flood plain management measures. <br /> <br />4.1 Flood Plain Boundaries <br /> <br />To provide a national standard without regional discrimination, <br />the 1 percent annual chance (lOO-year) flood has been adopted by <br /> <br />10 <br />