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1.49 <br />Q=----- x A x R~~3 x 5~~2 <br />n <br />where: <br />A = area of channel flow at depth of flow <br />n = Manning's roughness factor <br />R = hydraulic radius of channel in feet <br />( determined by dividing the area by the wetted perimeter) <br />S = gradient of channel in decimal A; <br />The parameters of the bridge crossing at the time of the picture <br />are given below. The key determining factor is flow depth, which <br />appears to be approximately 5 inches high. <br />Bottom Sides Flow Channel Manning's Velocity Flow <br />Width Slope Depth Slope n ft/sec cfs <br />feet <br />------ feet <br />----- ----- !k <br />------- const. <br />--------- <br />-------- ---- <br />14 2 0.42 .035 .030 5.0 31.0 <br />To this flow amount, the amount of flow leaving the ditch just <br />upstream from the bridge crossing must be added. From the picture <br />and the above estimate, it is very reasonable to assume that this <br />amount is approximately 25 cfs. Therefore, the combined amount of <br />56 cfs exceeds the peak flow of 49.4 cfs for the 10 year - 24 <br />hour storm. I fully realize that these calculations are not <br />precise, unfortunately we don't truly know the exact rainfall <br />amount and the exact period that it fell. Also, we have no flow <br />gage or weir in the drainage ditch. However, the calculations are <br />reasonable and I challenge the Division to prove that the storm <br />produced a flow that was under the peak flow from the 10 year - <br />24 hour storm. <br />As the calculations show, an event occurred on that day which <br />produced a runoff similar to that from a 10 year - 24 hour storm. <br />Therefore the discharge from Pond 15-P1 should also be exempt <br />