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FLOOD02208
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Last modified
1/25/2010 6:23:45 PM
Creation date
10/4/2006 10:41:43 PM
Metadata
Fields
Template:
Floodplain Documents
Designation Number
547
County
Gilpin
Community
Black Hawk
Basin
South Platte
Title
Draft Report - Reconstituition of 1979 Flood Peaks, North Clear Creek, Gregory Gulch, and Chase Gulch
Date
4/26/2001
Designation Date
5/1/2001
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />recommendations based on studies of mountain streams in Colorado (Jarrett, 1985). <br />Channel velocities were determined using an HEC-2 subcritical analysis of surveyed <br />cross sections or estimated using SCS velocity curves (SCS, 1986). <br /> <br />Curve Numbers were obtained following recommendations for Hydrologic Soil Group <br />"D" soils (SCS, 1986). Using this information, the per cent of land use in each catagory <br />in each catchment was determined using Figure 3, and average curve numbers were <br />calculated for each catchment. An average ARC (AMC) oflI was assumed. Please refer <br />to Table 1. Time of concentration calculations are shown in the Appendix. Time of <br />concentrations for each catchment are summarized in Table 2. <br /> <br />Table 1. Prelimina Curve Number Calculations Catchments 1-10, 1979 Land Use. <br />Land Use eN 1 2 3 4 5 6 8 9 10 <br />Area (ac) 5962 3875 5208 490 1884 810 691 1552 1870 <br />Area s .mi. 9.32 6.05 8.14 0.77 2.94 1.27 1.08 2.43 2.92 <br />High Density <br />Forest - D soil 79 65% 49% 64% 50% 65% 12% 48% 37% 69% <br /> <br />High Density <br />Forest ,A soil <br />(calibration) 36 0% 0% 0% 0% 0% 0% 0% 0% 0% <br />Low Density <br />Forest- D soil 83 19% 31% 21% 25% 15% 45% 21% 4% 0% <br />Meadow 75 16% 20% 10% 21% 20% 40% 31% 50% 23% <br />Low Density <br />Residential 84 0% 0% 5% 0% 0% 0% 0% 00/0 7% <br />Med. Density <br />Residential 90 0% 0% 0% 3% 0% 2% 0% 30/0 0% <br />Commercial 95 0% 0% 0% 1% 0% 1% 0% 6% 1% <br />Avera e eN 79 79 80 80 79 80 79 78 79 <br />Note: See Figure 3 for land use and Figure 4 for Catchment locations. <br /> <br />Table 2. Summa of Time of Concentrations, Catchments 1-10. <br />Catclnnen Tc Comment <br />hr <br />I 0.85 C6 <br />2 1.23 Silver Crk. + 45% NC5 to NC6 <br />3 1.82 Missouri G. <br />4 1.01 CC Catclnnent4 + NC3-NC4 <br />5 0.85 Chase VIS <br />6 1.26 Chase D/S + 80% CI-C2 <br />7 N/A <br />8 0.60 Gregory UlS <br />9 1.30 Gregory DIS (Pmsser G.) + 65% GI-G2 <br />10 1.24 Fourmile + 80% NCI-NC2 <br /> <br /> <br />Note: See Figure 4 for Catchment identification and design point locations. <br /> <br />-8- <br />
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