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Tailwater on the outlet -structure for maximum water level was assumed <br />to be 894.9. This was calculated using a water level downstream from <br />County Road H-2 or 894.5 and approximately 0.4 feet of head loss from <br />the outlet structure to a point south of the County Road. <br />Flows over the weir were calculated using the normal weir equation. <br />As noted above, the tailwater at the weir should not exceed the weir <br />sill elevation for the 100 year event. Calculations follow: <br />1. Orifice (893.0 to 894.9) <br />Use the normal inlet control charts from MnDOT. <br />Pond Elevation HW/D Q-cfs <br />893.5 <br />0.5 <br />0.8 <br />894.0 <br />1.0 <br />2.6 <br />894.5 <br />1.5 <br />3.6 <br />894.9 <br />1.9 <br />4.4 <br />At maximum pond, use the submerged orifice formula. Then <br />prorate discharge between 894.9 and 895.7. <br />Hw = 895.7 TW = 894.9 H = 0.8 ft. <br />0 = CA(2gh)� = 0.6(0.785)[2(32.2)O.8]k = 3.4 cfs <br />2. Weir <br />Calculation method from Kings "Handbook of Hydraulics" <br />Q = CLH3/2 <br />Elevation <br />C <br />L <br />H <br />H3/2 <br />O <br />895.1 <br />2.69 <br />4.8 <br />0.2 <br />0.0894 <br />1.15 <br />895.3 <br />2.72 <br />4.8 <br />0.4 <br />0.2530 <br />3.30 <br />895.5 <br />2.75 <br />4.8 <br />0.6 <br />0.4648 <br />6.60 <br />895.7 <br />2.85 <br />4.8 <br />0.8 <br />0.7155 <br />9.76 <br />3. Combination Orifice and Weir <br />Elevation Q-Orifice Q-Weir Q-Total <br />893.5 <br />0.8 <br />0.8 <br />894.0 <br />2.6 <br />2.6 <br />894.5 <br />3.6 <br />3.6 <br />894.9 <br />4.4 <br />4.4 <br />895.1 <br />4.2 <br />1.2 <br />5.4 <br />895.3 <br />4.0 <br />3.3 <br />7.3 <br />895.5 <br />3.7 <br />6.6 <br />10.3 <br />895.7 <br />3.4 <br />M <br />13.2 <br />E. Rating Curves for the outlet structure and pond storage are enclosed. <br />