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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />, <br /> <br />I <br />! <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />! <br /> <br />I <br />I <br />I <br />I <br />I <br /> <br />storms connected in a single 24 hour period. This type of occurance <br /> <br />would provide the high antecedent moisture condition III prior to one <br /> <br /> <br />of the high intensity periods, and would produce higher main channel <br /> <br /> <br />flow on the order of 13500 cfs at Academy Blvd. & Cottonwood Creek. <br /> <br /> <br />Main Channel Runoff could vary consider- <br />ably, depending on the type of storm. This condition is considered <br />in the appropriate section of this report. At the present time, this <br />area has been settled only about 120 years and accurate precipitation <br />records kept for less than 70 years. The true 100 year storm for the <br /> <br />area cannot be accurately known with such short term records. For <br /> <br />purposes of this report, the existing City design 100 year frequency ,~, <br /> <br />storm (Type II-A) has been used and is ;ecommended. ~// <br />Typical runoff hydrog~~ were computed <br />for points 6, 9 & 10 in the basin. These points are along Cottonwood <br /> <br />Creek and cOrrespond to the approximate location of Powers (point 6) <br /> <br />and the exact locations of Union Blvd. (point 9) and Academy Blvd. <br /> <br />(point 10). These hydrographs are based on the Type II-A storm and <br /> <br />assume relatively unobstructed flow through the channel. Hydrographs <br /> <br />for individual basins were not constructed except at points of recom- <br /> <br />mended retention ponds. These were necessary to determine approximate <br /> <br />required height and size of the pond. <br />The total basin was divided into three <br /> <br />major internal basins and the outfall point assigned for each. These <br /> <br />major internal basins were, in turn, divided into 40 minor internal <br /> <br /> <br />basins and an outfall point assigned to each. The peak flows were <br /> <br /> <br />routed along the three or four major channels by adding individual <br /> <br />-16- <br />