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<br />3 <br /> <br />regions classified as orographic in HMR 55A. The PMS <br />for the cherry Creek Drainage at 24 hours is <br />predominately (88 to 94 percent) non-orographic and is <br />even more so at shorter durations. <br /> <br />C. OTHER VALUES NEEDED FOR THE APPLICATION OF HMR 52 <br />TECHNIQUES (FIGURES 8 AND 39 IN THAT REPORT AND <br />APPENDIX A OF THIS STUDY) ARE AVAILABLE FOR THE CHERRY <br />CREEK DRAINAGE. <br /> <br />The strength of this approach for a site-specific study is <br />its continuity with the techniques used in HMR 52. Thus, the <br />limits to the volume of precipitation produced by the PMS <br />specifically for the Cherry Creek Drainage will arise from <br />consideration of the basin's shape, basin orientation with <br />respect to the climatological orientation of major storm <br />precipitation patterns, and from the hypothesis that nature is <br />limited in a PMS to producing maximum volume for just one storm <br />area size. This approach does not limit PMS volume by <br />restricting the storm data set considered applicable; all storms <br />explicitly or implicitly transposable to the Cherry Creek <br />Drainage contribute depth-area-duration values used by the HMR 52 <br />techniques. <br /> <br />If, however, the normalized, averaged within-storm depth- <br />area-duration relations from the twenty-nine major storms used in <br />HMR 52 presented an improper profile for the non-orographic <br />component of the PMS at the Cherry Creek Drainage, that would <br />weaken the credibility of the results obtained by using this <br />approach. In particular, concern could arise by considering that <br />onlY the three most intense 6-hour periods of precipitation are <br />subject to areal variation in the HMR 52 scheme. This <br />characteristic might be thought of as invalid for orographic <br />regimes since topography would continue to produce precipitation <br />gradients even if the orographically unperturbed atmosphere had <br />lost that potential after 18 hours of maximized production. Such <br />concern is not warranted at the Cherry Creek Drainage not simply <br />because the HMR 52 techniques used here apply only to the <br />non-orographic precipitation, but also because the 24-hour and <br />72-hour K-factors are at the low end of the range believed <br />applicable for orographic regions. The K-factors for shorter <br />durations are even lower at the Cherry Creek Drainage. <br /> <br />2. Analysis <br /> <br />In this study, it was assumed that the basin average depth <br />of total PMP for a given duration would be the summation of the <br />products of within-storm, non-orographic PMP at each and every <br />coordinate location in the cherry Creek Drainage for that <br />duration and within-storm K-factors developed for each and every <br />coordinate location for that duration. The product would then be <br />