FLOOD07105 - Laserfiche WebLink

Home Browse Search

I II-6 Storm Duration (hrs. ) I 6 24 TOTAL PRECIPITATION 2 YR IO YR Recur. Recur. Inter. Inter. (In. ) 100 YR Recur. Inter. 0.90 1.50 2.00 1.61 2.30 3.00 2.10 3.20 3.90 These data were compared to precipitation values recorded for the May 5 and 6, 1973 storm by the U.S.G.S. and reported in References 6 and 7. The data of Figure 111-2 was then tabulated for five-minute increments for the 2, 10 and 100 year recurrence interval storms. The five-minute incremental values were then rearranged according to the criteria of Reference 5 by placing the maximum increment between 20 and 25 minutes. The resulting storm pattern is consistent with the general arrangement of incremental precipitation of the thunderstorms in the Denver Metropolitan Area. The design storms used in this analysis are presented in Table 111-2. ~ 3. Storm Runoff The storm runoff peak values and total volume are dependent upon various factors, which include total precipitation, incremental precipitation pattern, infiltration rates, antecedent soil moisture conditions and basin character- istics. The total precipitation and incremental pattern chosen for this analysis (Section III-C-2) is based upon a thunderstorm type occurrence, since a thunderstorm precipitation arrangement yields higher peak flows. The peak runoff values are generally the critical design element for urban drainage facilities. One exception is the design of large storm detention reservoirs such as Hidden Lake where maximum inflow volume is critical. Therefore, a general type storm pattern was used for the design of Hidden Lake improve- ments (see Section III-E). Due to the relatively large size of Hidden Lake, " significant reductions in outflow are achieved. Therefore, the storm runoff