FLOOD07509 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I HYDROLOGIC ANALYSIS A detailed hydrologic analysis has been performed to define the peak flood flows and flood volumes for the 2-, 5-, 10-, 50-, and 100-year rainfall events assuming the future, fully developed basin and present channel conditions. While it is desirable to correlate measured precipitation and runoff characteristics of a drainage basin, little such recorded information is available for DF A 0054. Reliable rainfall, soils, and land use data are available for DF A 0054, however, and these data have been applied to the derivation of synthetic flood hydrographs for selected design points on the study reaches. Derivation of Hydrographs The procedure used in this study to derive the flood hydrographs is a modified test version of the "Colorado Urban Hydrograph Procedure" (CUHP), developed by the Urban Drainage and Flood Control District in 1979. The procedure is founded upon the synthetic unit hydrograph method developed by Snyder in 1938 and adjusted to reflect data locally collected and studies performed specifically for the Denver Metropolitan Area. The original CUHP is outlined in detail in Volume I of the Urban Storm Drainage Criteria Manual and the modified test version parameters may be obtained from the Urban Drainage and Flood Control District. Input parameters required for the CUHP are rainfall hydrographs and watershed parameters consisting of initial and final infiltration rates, decay rate, depression storage, sub-basin area, length, slope, centroidal distance, percentage of impervious area, and peak flow coefficients which reflect time to peak and relate to the peak rate of runoff. The drainage basin, subareas and channel configurations are shown on the Drainage Basin Map, Sheet 23 of the Drawings. Values for the DF A 0054 watershed parameters are listed in Table 1. Rainfall Data One-hour rainfall depths for the 2-, 5-, 10-, 50-, and 100-year return periods were derived from the "Precipitation-Frequency Atlas of the Western United States, Vol. Ill, Colorado" published by the National Weather Service but were not aerally reduced due to the small size of the basin. Temporal distributions of the storms were then determined using recent experimental data accumulated by the Urban Drainage and Flood Control District. The rainfall hyetographs used in this analysis are presented in Table 2 and graphically represented in figure 7. Table I WATERSHED PARAMETERS Basi n A L Lc S Percent Kt" Cp" Ct" Initial Final Area Basin Centroidal Slope Impervious Infiltration Infiltration (Acres) Length Distance (ft/ft) (In ches) (Inches) (Miles) (M iles) (Hour) (Hourf FUTURE LAND USE Al 74.6 .44 .16 .0152 41 .090 .413 .156 3.0 .5 A2 107.5 .62 .19 .0129 40 .090 .412 .174 3.0 .5 A3 225.8 .87 .31 .0204 43 .090 .418 .177 3.0 .5 A4 174.5 .93 .35 .0291 40 .091 .407 .169 3.0 .5 A5 94.4 .93 .42 .0128 25 .101 .332 .231 3.0 .5 A6 60.0 .58 .27 .0286 10 .111 .250 .187 3.0 .5 A7 121. 9 .73 .35 .0284 10 .111 .250 .201 3.0 .5 A8 76.8 .78 .36 .0193 10 .111 .250 .221 3.0 .5 A9 104.6 .74 .34 .0100 10 .111 .250 .216 3.0 .5 B1 78.9 .74 .38 .0240 10 .111 .250 .211 3.0 .5 B2 107.9 .95 .47 .0268 10 .111 .250 .220 3.0 .5 C1 101. 9 .63 .28 .0209 28 .099 .346 .182 3.0 .5 C2 142.9 .95 .44 .0301 10 .111 .250 .212 3.0 .5 C3 91.5 .77 .37 .0272 10 .111 .250 .206 3.0 .5 C4 100.6 .81 .28 .0258 10 .111 .250 .201 3.0 .5 C5 71.3 .53 .32 .0361 10 .111 .250 .180 3.0 .5 " Based on Modified Test Version of CUHP being developed by the Urban Drainage and Flood Control District C _ Kt (LLc)0.14 t - SO.22 -8-