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FLOOD03876
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Last modified
1/25/2010 6:44:36 PM
Creation date
10/5/2006 12:09:04 AM
Metadata
Fields
Template:
Floodplain Documents
County
Clear Creek
Community
Idaho Springs
Basin
South Platte
Title
Flood Insurance Study - City of Idaho Springs
Date
5/1/1978
Prepared For
City if Idaho Springs
Prepared By
FEMA
Floodplain - Doc Type
Historic FEMA Regulatory Floodplain Information
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<br />For the other streams studied in this report, peak discharges were <br />determined using a series of regression equations from which flood <br />characteristics can be estimated from measurable physical and <br />climatic parameters of drainage basins. <br /> <br />The results of the cited regional hydrologic analyses were compared <br />to statistical analyses of historical discharge records on Clear <br />Creek at Lawson operated by the u.s. Geological Survey (References 3, <br />4, 5, 6, and 7). Analysis of this station followed ,the standard log- <br />Pearson Type III method, as outlined by the U.S. Water Resources <br />Council (Reference 8). Comparison of records on Clear Creek at <br />Lawson with results of the regional hydrologic analysis showed a <br />maximum difference in floodflows of 29 percent and an average <br />difference of only 10 percent. This error is acceptable, considering <br />the uncertainties inherent in the analysis and the short period of <br />record. The regional analysis was, therefore, adopted for use in <br />Clear Creek County for both gaged and ungaged areas, and was also <br />adopted to the City of Idaho Springs. <br /> <br />Peak discharge-drainage area relationships for Clear Creek, Soda <br />Creek, Virginia Canyon, and Chicago Creek are shown in Table 1. <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 elfivations of <br />floods of the selected recurrence intervals along each stream <br />studied in the community. <br /> <br />Water-surface elevations of floods of the selected recurrence <br />intervals were computed through use of the U.S. Army Corps of <br />Engineers HEC-2 step-backwater computer program (References 9, 10, <br />and 11), and supplemented by manual calculations. Manual calculations <br />were primarily used to determine the division of floodflows at <br />bridge sections and to verify water-surface elevations near bridge <br />sections and to verify water-surface elevations near critical <br />depth. <br /> <br />Cross sections for the backwater analyses were field surveyed and <br />located at close intervals above and below bridges and culverts in <br />order to compute the significant backwater effects of these structures <br />in the urbanized areas. <br /> <br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1). For stream segments <br />for which a floodway is computed (Section 4.2), selected cross <br />section locations are also shown on the Flood Boundary and Floodway <br />Map (Exhibit 2) . <br /> <br />6 <br />
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