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MCOB, PHASE II <br /> Calculation: C-5 <br /> Design of Outfalls Page 2 of 2 <br /> Design Basis: <br /> The flow splitters and outfalls to Merrill Creek will be reconstructed in their same general locations as the <br /> existing conditions. The amount of flow tributary to each flow splitter has changed very slightly since the <br /> original design due to how the tributary areas changed with the removal of the trench drain. Two of the <br /> outfall pipes will be upsized from 15"pipes to 18"pipes since the proposed slope is less than the existing. <br /> Flow rates and velocities discharging into Merrill Creek have been estimated below in order to evaluate the <br /> outfall protection that may be necessary. <br /> Methods and Assumptions: <br /> Continuous modeling software was used in this calculation to determine the peak flowrates at the outfalls. <br /> For this calculation,it was assumed that the entire runoff tributary to the flowsplitter goes out the overflow <br /> pipe. The velocities were calculated assuming the outfall pipes are flowing full.Velocity is equal to the <br /> flowrate divided by the pipe area. <br /> The following software was used for this calculation: <br /> - AutoCAD C3D 2016—project site tributary area information <br /> - WWHM2012—continuous modeling software for stormwater runoff flowrates <br /> Findings and Conclusions: <br /> Outfalls <br /> Structure Total Area Pipe Size(in) 10 YR PEAK 10 YR 100 YR 100 YR <br /> ID Tributary (cfs) VELOCITY PEAK(cfs) VELOCITY <br /> (acres) (ft/s) (ft/s) <br /> 600 5.18 18 2.71 1.53 4.35 2.46 <br /> 500 4.59 18 2.40 1.36 3.85 2.18 <br /> 400 3.05 12 1.59 2.03 2.56 3.26 <br /> 300 3.03 12 1.58 2.01 2.54 3.24 <br /> 200 2.02 12 1.06 1.35 1.70 2.17 <br />