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<br />2 <br /> <br />collection of among-storm precipitation depths for <br />various storm area sizes and durations in which <br />individual storms maximize describes a synthetic or <br />composite storm. When the among-storm precipitation <br />being discussed is PMP, the synthetic or composite <br />Probable Maximum Storm (PMS) is a collection of extreme <br />values (depths) coming (typically) from a variety of <br />specific, individual storms, each of which has <br />"maximized" at a different storm area size or duration. <br /> <br />within-storm precipitation values (depths) <br />describe the depth-area-duration characteristics of a <br />specific, individual storm and consist of depths onlY <br />from that storm. When the within-storm precipitation <br />being described is a PMS, then there will be many storm <br />area sizes and durations for which this storm will <br />produce depths less than that of PMP, while still <br />producing PMP at some area size and for a range of <br />durations. <br /> <br />. <br /> <br />An index map of non-oroqraohic PMP for 10-mi2 and 24- <br />hours used in deriving Plate IIIb of HMR 55A (Figure <br />8.7 and Appendix B of this study) was available along <br />with 1- to 6-hour, 6- to 24-hour, and 72- to 24-hour <br />depth-duration ratio maps (section 10.3 of HMR 55A) <br />which extend into the region just east of the OSLo <br />From this information, it was possible to develop the <br />among-storm distribution of non-orographic PMP in and <br />around the Cherry Creek Drainage for the four key <br />durations of 1, 6, 24, and 72 hours. When these maps <br />are used in combination with depth-area-duration <br />relations for non-orographic regions (section 11.3.3 of <br />HMR 55A), the non-orographic PMP values for the <br />standard area sizes and durations used in HMR 52 can be <br />derived. <br /> <br />B. TECHNIQUES CAN BE DEVISED TO DEFINE THE INTERACTION <br />OF THE WITHIN-STORM NON-OROGRAPHIC DEPTHS WITH <br />OROGRAPHY. <br /> <br />The first step was to divide values from Plates Ib-IVb <br />from HMR 55A by the corresponding non-orographic index <br />map values developed for this study to obtain the <br />among-storm orographic factors (K-factors). Based on a <br />key hypothesis to be discussed below, the K-factors <br />could then be used to modify the within-storm, non- <br />orographic values of PMP developed from HMR 52 <br />techniques, to produce within-storm values of total <br />PMP. In deriving the K-factors, it was found that at <br />24 hours, the range of K-factors in the cherry Creek <br />Drainage was between 1.06 and 1.14. These values are <br />decidedly in the lower range of those found in the <br />