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Col 17: <br /> The storage requirement for the retention pond is capacity to hold 2 - 100 year <br /> storms. However, for pipe system drainage calculations, the upper water surface <br /> under conditions of storage of One 100 - year storm is assumed to be in the basin <br /> (WS elevation is 19.4 (See Sheet 2 of 4, Attachment 1). Column 17 calculates the <br /> HGL for the three gravity flow outfall pipes to the pond under this condition. <br /> Note that the calculated HGL:s for outfall pipes, based on depth of flow in the <br /> pipes, are all greater than the pond WS=19.4. <br /> The HGL was calculated in column 11 proceeding from the pond in the upstream <br /> direction based on the assumption that the rise in the HGL is equal to the pipe <br /> slopes (minor losses are neglected). Column 17 calculates the distance of the <br /> HGL below the grates for these conditions. Depths exceed I foot in compliance <br /> with County Standards. <br />