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AS = pond surface area (square feet) <br />h = head of water above orifice (height of riser in feet) <br />T = dewatering time (24 hours) <br />g = acceleration of gravity (32.2 feetlsecond2) <br />Convert the orifice area (in square feet) to the orifice diameter D (in inches): <br />D=24x `°=13.54x Ao <br />The vertical, perforated tubing connected to the dewatering orifice must be at least 2 inches larger in <br />diameter than the orifice to improve flow characteristics. The size and number of perforations in the <br />tubing should be large enough so that the tubing does not restrict flow. The orifice should control the <br />flow rate. <br />2019 Stormwater Management Manual for Western Washington <br />Volume 11 - Chapter 3 - Page 391 <br />