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<br />I, <br /> <br />C, HYDROLOGY <br />The Colorado Urban Hydrographic Procedure (CUHP) was used to analyze the runoff from each <br />sub-basin. Table I summarizes the hydrologic characteristics of each sub-basin, The data provided <br />in Table I was used as input to the model. The output from the model are the runoffhydrographs <br />from each sub-basin, ,which are then used as input to the Storm Water Management Model <br />(SWMM), <br /> <br />Rainstorms that have a duration that exceeds six-hours can produce large amounts of total <br /> <br /> <br />precipitation; however, these storms are rarely intense and seldom result in urban flooding <br /> <br /> <br />problems. Very intense rainfall in the Aspen area usually results from convective storms and <br /> <br /> <br />frontal stimulated convective storms. These types of storms are often less than one-hour or two- <br /> <br /> <br />hours in duration and can produce brief periods of high rainfall intensities, These short duration <br /> <br /> <br />intense rainstorms appear to cause most of the urban flooding problems, <br /> <br />The recommended design storm distribution takes into account the observed "leading intensity" <br />nature of the convective storms. In addition, the temporal distributions were designed to be used <br />with CUHP, the published NOAA one-hour precipitation values, and the Horton's iniiltrationloss <br />equation, They were developed to approximate the recurrence frequency of peak flows and <br />volumes (Le" 2-Year through laO-Year) that were estimated for the watershed for which <br />rainfall/runoff data was collected, The procedure for the design storm distributions and the <br />preliminary results were reported atthe 19791ntemational Symposium on Urban Storm Runoff, <br />Table 2 presents the rainfall distribution for a two-hour storm event over the City of Aspen for the <br />2-year, 5-year, la-year, 50-year, and lOa-year frequencies. Table 3 supplies the results of the <br />CUHP modeling and provides the peak flows from each sub-basin shown in Figures 1 through 4, <br /> <br />3 <br />