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. I . .. II , . I . I . I I I . I . I . I I I I ~x:-'? the entire basin. This type of storm is that for which City of \., ~./\ 1 1(, e\ Colorado Springs drainage structures have been designed since 1963. The rainfall criterion have been changed in that time, of course, as new data becomes available. The Type IIA storm used as the local criterion for design is a storm of six hour duration, but with an approximate one hour burst during the second hour. It is not greatly different in character from the one hour storm used until 1972. This basin is relatively large but is not so large that it could not be covered by such a thunderstorm. of. ,-7'/) ~"Jll 0 ~ I(f The computations used in this study are based on such an intense storm, centered at about point four in the basin, and falling at the same rate over the entire basin. This configuration will yield the peak runoff for the design storm. Such storms actually move from west to east, which tends to reduce the flood peak in the developed area. Several storm patterns were investigated in this study to determine the location resulting in the probable high runoff for a Type II-A storm. One important fact must be considered 1'/ :I' 7')\ ,(bY. in assigning a rainfall pattern or intensity to this basin. The upper portion of the basin lies under an area which is described as a major storm axis, generally east of colorado Springs, The moun- tains to the west, particularly the Pikes Peak massive, tend to produce a storm shadow along the valley of Monument Creek. With some notable (and recent) exceptions, the centers of major storms tend to be located along this axis, This axis is not a line, incidently, but rather a strip about six miles in width centered on Black Forest and Peterson Field. -14-