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<br />Hydrology and Hydraulics
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<br />Hydrolo~ - This phase of the study includes the development of peak
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<br />discharge values for various flood frequencies at selected locations.
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<br />A frequency analysis of streamgage records was made in accordance with
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<br />Water Resources Council Bulletin 17. These values were compared with
<br />data from Colorado Water Conservation Board (CWCB) Technical Manual
<br />No.1. Discharge values obtained using the CWCB Manual were slightly
<br />higher and were selected for use in this study. This procedure provided
<br />peak discharge-frequency values at the Cottonwood Creek streamgage site.
<br />Values at several locations along the stream were determined and a drain-
<br />age area vs. peak discharge curve was developed for convenience and to
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<br />ma i nta i fl cons i stency in se lect i ng flows at other locat ions..
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<br />Hydraulics - The hydraulic analyses were based on the SCS Water Surface
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<br />Profile Computer Program, WSP-2. Input data for this program includes:
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<br />cross-section information, reach lengths, contributing drainage area
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<br />measurements, channel and flood plain roughness coefficients, and dis-
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<br />charge values. The cross-section, reach length, and drainage area data
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<br />was obtll i ned from fi e 1 d' surveys and photogranmetri c maps prepared
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<br />especially for. this study. Typical "n" values (roughness coefficients)
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<br />range from 0.045 to 0.110 and were determined from photographs and field
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<br />inspection.
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<br />Through the use of the WSP-2 computer program, flood crest elevations
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<br />for the 10-, 50-, 100-, and 500~year floods were determined. These
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<br /> TABLE 2
<br /> ELEVATION REFERENCE MARKS 11
<br />Flood Ha4ard Map Reference
<br />Sheet Number Mark Elevation Coordinate
<br /> 2 BC-5 7934.08 N 364,477.277
<br /> E 1,821,436,257
<br /> 2 BC-15 7955.46 N 368,047.316
<br /> E 1,820,248,954
<br /> 3 BC-14 7977.68 N 367,915,233
<br /> E 1,817,862.808
<br /> 4 BC-6 7987.74 N 370,748.43
<br /> E 1,818,452.857
<br /> 5 BC-13 8052_47 N 365,989.357
<br /> E 1,813,120.388
<br /> 6 BC-7 8045.05 N 369,748_57
<br /> E 1,813,229.63
<br /> 7 BC-l1 8193.60 N 362,239.166
<br /> E 1,805,404.533
<br /> 7 BC-12 8163,74 N 365,845.080
<br /> E 1 ,807,761 ,028
<br /> 8 BC-lO (0-1) 8382.40 N 358,955,81
<br /> E 1,800,071.06
<br /> 8 BC-9 8281_38 N 361,785.45
<br /> E 1,802,536.62
<br />l! The above Elevation Reference Marks are shown on the Flood Ha4ard
<br /> Area Maps (Sheets 1-8).
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<br />C-3
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