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<br />DRAINAGE CRITERIA MANUAL <br /> <br />RUNOFF <br /> <br />identical input data. It is therefore important that only one routing method <br />be used when analyzing a watershed. In other words, do not switch routing <br />techniques from reach to reach. Stay with a single method throughout all <br />reaches in the watershed. <br /> <br />4.14 Basis for 1982 Version of CUHP <br />Rainfall and runoff data were collected by U.S. Geological survey in the <br />Denver metropolitan area since 1969 under a cooperative agreement with the <br />Urban Drainage and Flood Control District. Analysis of this data by the <br />District staff began in earnest in 1977. Of the original thirty gaging <br />stations, data from only seven sites (nine different basin conditions) were <br />used by the District to develop the 1982 version of the cUHP. Data from all <br />other sites were evaluated and were determined not suitable for use due to <br />various gaging problems and watershed definition problems. Because the <br />metropolitan area data base lacked an undeveloped watershed, data from a small <br />watershed (Kiowa Creek Tributary at Elbert) being gaged by USGS for the <br />Colorado Highway Department was used to round out the mix of land uses in the <br />data base. <br />Table 4-7 presents a summary of rainfall/runoff data base and includes <br />the key watershed parameters for each site. For each of the dates that data <br />were available, a complete rainfall depth record and concurrent flow <br />measurements at 5-minute time increments served as the basis for the <br />development of the revised CUHP. Peak flows from each recorded hydrograph are <br />compared with the calculated peak flows using the 1982 version of CUHP in <br />Figure 4-8. This comparison substantiates the validity of the new CUHP <br />procedure. <br />Those wishing to compare the older version of the cUHP with the new <br />version will find that often the new unit hydrograph will have a significantly <br />shorter time to peak. This is particularly true for smaller urbanized basins. <br />However, the new vers ion wi 11 often produce peak flow resul ts comparable to <br />those obtained using the old version over a wide range of watershed conditions <br />typically used in drainage studies in the Denver Metropolitan Area. <br /> <br />5-1-84 <br /> <br />. <br /> <br />. <br /> <br />. <br />