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1. Colorado extreme precipitation events are significantly smaller in their depth, duration and aerial coverage than the storm characteristics ofHMR 52 that rely on 29 storms sampled over the eastern two-thirds of the country (See Figure 1). 2. The major axis of the rainfall pattern extends along the direction of the winds in the storm cloud layer (+/- 10 degrees). The surface wind direction is 40 to 90 degrees to the right of the cloud layer winds (See Figure 2). In effect, this relationship of meteorology to rainfall pattern must be maintained during the transposition of storms into a basin to keep the transposition process "physically possible". The final PMP design storm must also maintain this relationship. Figure 1 shows that Colorado storms are smaller than the HMR 52 storms. The Colorado storms range from 66% to 91 % of the HMR 52 storms for area sizes ranging from 5,000 square miles down to 100 square miles. HMR 52 requires the use of its storm sample together with their rainfall distribution curves without offering any other alternative. This finding supports the fact that the use ofHMR 52 within/without curves is inappropriate in the Cherry Creek basin due to major differences between the Colorado storms and those used in HMR 52. Comparison of Average Within / Without Storm Curves for Different Study Regions to-Square Mile Area Size 10000 r--.. 00 ..!:i ~ ::: 1000 (\l ;:I C" rJl .5 <l.l N ;;; (\l <l.l < E 2 rJl -+- Colorado Front Range _Colorado East of Foothills ---+- Colorado Eastem Plains 100 ---ilE-- Storms U sed in HMR 52 10 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 Percent of 24-hr Rainfall Amounts Figure 1 Comparison of Average Within / Without Storm Curves for Different Study Regions X111