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Pipe Design <br /> The pipe is 1/4 inch thick smooth steel pipe of an inside diameter <br /> of 9 . 0 feet . It is Core 10 steel , well suited for tough , permanent <br /> installations . A Manning ' s n of 0 . 017 is used for the smooth steel <br /> pipe . If the pipe is flowing half full , the area is : <br /> Area (A) = (3. 14 x r2)/2 for 1 /2 pipe r = 4 . 5 A = 31 . 8 ft2 <br /> Wetted Perimeter (P) = 2 x 3. 14 x r/2 = 14 . 14 <br /> Hydraulic radius = A/P = 2 . 249 <br /> The 9 ft . pipe will be laid in the existing trough for a distance <br /> of 180 feet . The channel grade in this section is 4 . 16%. <br /> Using Manning ' s equation with the above parameters yields a peak <br /> flow of 573 cfs . Since a safe design flow is 500 cfs , the pipe is <br /> adequate. <br /> Drawing 1 shows how the pipe will be laid in the concrete trough . <br /> Pipe Entrance Design <br /> In order to prevent the pipe from clogging at the entrance from a <br /> debris event , it is important that the transition from the 11 . 7 <br /> feet wide trough to the 9 ft . diameter pipe be as smooth as <br /> possible. The revised Drawing 11-B-7 Att 6-21 shows how a custom- <br /> concrete transition will perform this task . Compacted dirt around <br /> the entrance as shown will provide a safety factor for an event <br /> larger than the 100 year event . If a larger event occurs , the <br /> entrance may control flow, but the pipe will flow to a level of 6 .0 <br /> feet without any overflowing of the entire diversion system. <br /> By compacting dirt around the pipe entrance and by extending the <br /> concrete transition into the pipe, all water must flow in the pipe <br /> and cannot flow in the concrete trough . <br /> /�1zIq <br /> 3 <br />