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FLOOD05002
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Last modified
1/25/2010 6:47:56 PM
Creation date
10/5/2006 1:10:50 AM
Metadata
Fields
Template:
Floodplain Documents
Designation Number
209
County
Prowers
Community
Lamar
Basin
Arkansas
Title
Flood Insurance Study - Lamar, Prowers County, Colorado
Date
5/1/1982
Designation Date
1/1/1983
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />having a fl ood which equal s or exceeds the 100-year flood (1 percent chance <br />of annual occurrence) in any 50-year period is approximately 40 percent (4 <br />in 10), and, for any 90-year period, the risk increases to approximately 60 <br />percent (6 in 10). The analyses reported here reflect flooding potentials <br />based on conditions existing in the county at the time of completion of <br />this study. Maps and flood elevations will be amended periodically to <br />refl ect future changes. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out by the U.S. Army Corps of <br />Engineers (Reference 1) to establ i sh the peak di scharge- frequency <br />relationships for floods of the selected recurrence interval s. Flows <br />on the Arkansas River from the U.S. Army Corps of Engineer's <br />hydrology report were obtained using a synthetic unit hydrograph for <br />ten subareas of the Arkansas River basin and routing them to Lamar, <br />as described by the method in EM1110-2-1408, "Routing of Floods <br />through River Channels" (Reference 4). Flows on Willow Creek were <br />calculated by the U.S. Army Corps of Engineers using a synthetic unit <br />hydrogra ph that was developed from a flood event on Salt Draw near <br />Orla, Texas. The flows were compared to a gage station analysis of <br />the Arkansas River U.S.G.S. gage at Lamar. The Arkansas River at <br />Lamar gage ha s a peri od of record of 1921 to the current year, wi th <br />the data from 1944 to the current year refl ecti ng the operation of <br />John Markin Reservoir. The peak flows obtained by the U.S. Army <br />Corps of Engineers, in their gage analysis, agreed with the unit <br />hydrograph analysis. The study contractor checked this gage analysis <br />by using Reference 5, and obtained peak flow rates within the 90 <br />percent confidence 1 imits of the frequency-di scharge curve obtai ned <br />in the "Review Survey for Water Resource Development, Lamar, <br />Colorado, and Vicinity, Hydrology (Revised) 1978" (Reference 1l. The <br />peak discharges used in this study are shown in Table 1. <br /> <br />Table 1 - Summary of Discharges <br /> <br />Drainage Area <br />(square mile) 10-Year <br /> <br />Peak Discharge (cfs) <br />50-Year 100~Year 500-Year <br /> <br />Flooding Source <br />and Location <br /> <br />Arkansas River <br /> <br />A t Lamar <br /> <br />19,780 <br /> <br />11 ,200 <br /> <br />28,000 <br /> <br />40,000 <br /> <br />84,000 <br /> <br />Willow Creek <br /> <br />At Siphon <br />3.2 Hydraulic Analyses <br /> <br />40 <br /> <br />2,900 <br /> <br />8,600 <br /> <br />12,800 <br /> <br />28,400 <br /> <br />Analyses of the hydraulic characteristics of the flooding sources <br />studied in detail in the community were carried out to provide esti- <br /> <br />6 <br />
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