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FLOOD06596
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Last modified
1/25/2010 7:09:26 PM
Creation date
10/5/2006 2:23:53 AM
Metadata
Fields
Template:
Floodplain Documents
Designation Number
393
County
Lincoln
Community
Limon
Basin
Arkansas
Title
Flood Insurance Study - Limon, CO, Lincoln County
Date
5/1/1984
Designation Date
1/1/1995
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />A number of references were used to check the reasonableness of <br />the discharge-drainage area curve. Some of these include data <br />from Technical Manual No. 1 (Reference 6), the U.S. Soil Conservation <br />Service Curve Number Method, U.S. Geological Survey Water-Supply <br />Paper 1681 (Reference 7), historical peak discharges, and discharge- <br />frequency data from other available studies. <br /> <br />". <br /> <br />Reservoir construction on the three tributaries to Big Sandy Creek <br />significantly modified flows downstream from the dams. The uncon- <br />trolled drainage area below the dams was used to develop discharge- <br />frequency values for the tributaries. A base flow reservoir release <br />rate was added in as a contributor to the peak discharge. This <br />release rate was determined by developing and routing inflow hydro- <br />graphs through the reservoirs for various storm frequencies used <br />in this study. The inflow hydrographs and routings were accomplished <br />using the U.S. Soil Conservation Service DAMS-2 computer program <br />(Reference 8). <br /> <br />Peak discharge-drainage area relationships for Main, East, Middle, <br />and West Tributaries as well as Big Sandy Creek are shown in Table 1. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of flooding from the <br />sources studied were carried out to provide estimates of the eleva- <br />tions of floods of the selected recurrence intervals. <br /> <br />Cross section data and reach length information were obtained from <br />photogrammetric maps prepared especially for this study. <br /> <br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1) and on the Flood Boundary <br />and Floodway Map (Exhibit 2). <br /> <br />Hydraulic roughness coefficients (Manning's "n") were determined <br />from field inspection and documented with photographs (Reference 9). <br />Following is a tabulation of the range of roughness coefficients <br />used for the detailed-study streams. <br /> <br />Stream <br /> <br />Channel <br />Values <br /> <br />Overbank <br />Values <br /> <br />Main Tributary <br />East Tributary <br />Middle Tributary <br />West Tributary <br />Big Sandy Creek <br /> <br />0.060-0.075 <br />0.045-0.060 <br />0.045-0.060 <br />0.045-0.060 <br />0.045 <br /> <br />0.040-0.110 <br />0.040-0.050 <br />0.040-0.100 <br />0.040-0.110 <br />0.050 <br /> <br />Water-surface elevations for 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 (Reference 10). <br /> <br />9 <br />
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