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FLOOD11727
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Last modified
1/26/2010 10:23:54 AM
Creation date
5/19/2008 2:17:14 PM
Metadata
Fields
Template:
Floodplain Documents
Designation Number
221
County
El Paso
Community
Manitou Springs
Basin
Arkansas
Title
FIS - Manitou Springs
Date
8/1/1983
Designation Date
1/5/1984
Prepared For
Manitou Springs
Prepared By
FEMA
Floodplain - Doc Type
Historic FEMA Regulatory Floodplain Information
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<br />along the centerline of the 100-year flow path. On the maps, <br />this flow line, used to establish profile distances, is delineated <br />and labelled as the Profile Base Line. <br /> <br />The hydraulic analyses for Sutherland Creek, Williams Canyon, <br />and Ruxton Creek are based on unobstructed flo\\,. The flood eleva- <br />tions shown on the profiles are thus considered valid only if <br />hydraulic structures remain unobstructed, operate properly, and <br />do not fail. <br /> <br />- <br /> <br />The hydraulic analysis for Fountain Creek as developed by the <br />U.S. Army Corps of Engineers, is based on an assumption of limited <br />clogging. The U.S. Army Corps of Engineers considers limited <br />clogging to be 10 percent of culvert areas and 1 foot on each <br />side of bridge piers. These values may vary from structure to <br />structure depending on field evaluation of structure configuration. <br /> <br />Flow breakouts for floods greater than the lO-year discharge on <br />Fountain Creek occur at the U.S. Highway 24 bridge crossing. <br />These breakouts flow through the Manitou AvenUE~ underpass and <br />rejoin Fountain Creek at cross section C. As a result, the peak <br />discharges for the 50-, 100-, and 500-year floods were reduced <br />700, 2,lOO, and 9,250 cubic feet per second (cfs), respectively. <br /> <br />Inadequate channel capacities of Sutherland Cn~ek downstream of <br />cross section A, coupled with the inadequate culvert capacity <br />under the U.S. Highway 24 Access Road, result in breakouts of <br />flow greater than the lO-year flood. Breakout flows occur in <br />both the east and west overbanks. The lack of any defined flow <br />channels results in a complex flow pattern which consists of overland <br />flow and flow along U.S. Highway 24. These flows, joined with <br />the breakout flows from Fountain Creek, cannot be modeled with <br />a one-dimensional backwater model. Therefore, no elevations have <br />been determined for the downstream portion of Sutherland Creek <br />and the flows along U.S. Highway 24 and Manitou Avenue. Therefore, <br />the flood hazard area has been analyzed by approximate methods. <br /> <br /><.I <br /> <br />The approximate elevations for upper Williams Canyon and for Beckers <br />Lane Tributary were developed using cross sections taken from <br />a U.S. Geological Survey topographic map enlarged to a scale of <br />1:4,800, with a contour interval of 40 feet (Reference lO) and <br />the U.S. Army Corps of Engineers HEC-2 computer program (Reference 7), <br />which generates a top width for each section based on cross section <br />area, drainage area, 100-year discharge, slope, and roughness <br />values. <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 />Q <br /> <br />. <br /> <br />12 <br />
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