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<br />,--~'- <br /> <br />I <br />I <br />'I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Elevation Acres % of Total Area Acre Feet Total <br />935-936 .01 .1 .005 <br />936-938 1. 30 20.1 1.325 <br />938-940 1. 34 20.7 5.285 <br />940-942 0.39 6.1 10.975 <br />Above 942 3.27 50.7 <br /> <br />The existing hydrology can be evaluated on the <br />basis of water level by calculating the size of <br />storm required to raise the water level signifi- <br />cantly. <br /> <br />If six inches of rain fall on the site and 50% of <br />the rainfall is absorbed by the soil, the volume <br />of water retained on the site for ponding will be <br />1.61 acre feet. The water to be retained is com- <br />puted thusly: <br />percent of land (0.50) x rainfall (6 inch) x <br />l' <br />12" x drainage area (6.45) = 1.61 acre feet <br /> <br />If it is assumed the pond is initially dry, the <br />surface elevation of the water will rise to approxi- <br />mately 938.2 feet in accordance with the above <br />table. This rationale can now be combined with <br />some assumptions about the November 1975 conditions <br />to provide approximate figures of how a storm af- <br />fects the site today: <br />Assume: The pond water elevation is at 937.5 <br />with 0.90 acre .feet in storage on the <br />site. The occurrence of a 12 hour, 100 <br />year storm (5 inches of rainfall in 12 <br />hours). Coefficient of runoff would be: <br /> <br />I <br />I <br /> <br />on water: 1. 00 x 1.2 acres = 1.2 <br />on soil: 0.25 x 5.25 acres = 1. 31 <br /> 2.51 <br /> 2.51 . 6.45 = 0.39% runoff <br /> <br />III-II <br />