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<br />. <br /> <br />Finally, the southerly flow af air towards Palmer Divide assists in the formation <br />and maintenance of a low ievel wind eddy known as the "Colorado Springs <br />Cyclone" (CSC). This low level eddy spins counterclockwise over the vicinity of <br />the City of Colorado Springs and the Air Force Academy, In effect the CSC acts <br />to intensify and focus storm intensification away from Pikes Peak and over' <br />Palmer Divide and the plains to the east. PI similar but better documented low <br />level eddy is the Denver Cyclone (Rappalt and Henz, 1993), The Denver <br />Cyclone has been associated with the enhanced occurrence of severe weather <br />and heavy rainfalls in the Denver metropolitan area to the north. Similar impacts <br />are likely with the CSC, though storm intensification would be favored at much <br />lower elevations to the north and east of Mason Reservoir. <br /> <br />Consideration of these three orographic; factors supports the assumption <br />that the zone of most likely storm formation and intensification would <br />occur at elevations below 1 0,500 feet in a zone oiF tight elevation gmdient <br />between 7,500 feet and 9,000 feet. In an independent paleohydrologic flood <br />investigation of the Pikes Peak region affecting Manitou Springs and Colorado <br />Springs, Jarrett (1987) concluded that no ev"dence of substantial flow or <br />flooding was evident at elevations above 8,000 feet in the basins <br />surrounding Pikes Peak. These two observational studies support the <br />result of the HMS basin orographic survey. In effect, the evidence <br />supports the existence of a naturally occurring precipitation potentiial <br />reduction mechanism for the Mason Reservoir drainage basin. <br /> <br />4.0 HMR 55A site-specific local and general st,:>rm PMP calculations <br /> <br />HMS is pioneering innovative approaches to the calculation of site,-specific local <br />storm and general storm PMP in the higher elevation areas of the western United <br />States. However, it recognizes the importance of maintaining continuity between <br />these innovative approaches, the approaches of prior PMP studies, and the <br />standard approaches to PMP as given in the HMR series, In this section, !-IMS <br />uses the standard HMR 55A methodology for historical storm in-place moisture <br />maximization, storm transposition, and moisture adjustments for elevation, This <br />standard methodology was applied to the storms identified in Tables 1 and 2 for <br />the Mason Reservoir drainage basin, <br /> <br />Since the drainage basin for Mason Reservoir has an area of less than 10 <br />square miles, PMP spatial reduction considerations are minimal and are not <br />computed, It is assumed that the core of either the local or general storm <br />precipitation maximum is positioned to cover the entire drainage basin unless <br />orographic considerations dictate otherwise, In this case, additional information <br />on storm placement will be provided. A basin map for each event is not <br />appropriate given the small size of the basin, HMS c10es not use the <br />isopercental technique in storm transposition because of concerns that the <br />characteristics of rainfall intensity and distribution associated with '100 year' <br /> <br />24 <br />