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I I I I I I I I I I I I I I I I I I I I 3.2 Flood Routing Reservoir routing was performed using the U.S. Army Corps of Engineer's flood hydrograph computer model, HEC-l. The following conditions were used for the routing of the PMF. The crest of the primary spillway was raised 5 feet from elevation 6365 to 6370. This results in an increased reservoir capacity of approximately 2,400 acre-feet. The primary spillway head-di scharge relationship is assumed to remain unchanged at the new elevation; therefore, discharge is governed by the relationship found on the original design drawi ngs. The auxiliary spillway is located at elevation 6375. The control section has a trapezoidal shape with a bottom width of 150 feet and 2H to lV side slopes. Upstream of the control secti on is a flared trapezoi da 1 entrance channel approximately 450 feet in length at elevation 6375. The auxiliary spillway chute downstream of the control section is an unlined channel in rock for a length of approximately 350 feet, and is set at a 3 percent slope. Supercritical flow will occur in the chute. Critical discharge was assumed at the control section of the auxiliary spillway. The net head available was reduced by 10 percent to account for friction and convergence losses occurring in the entrance channel. The combined discharge capacity of the primary and auxiliary spillways were used to generate a si ngl e di scharge curve for the pr~F routi ng. Reservoi r routing of the P~'F for the conditions described above resulted in a computed maximum water surface el evati on of 6383.5 feet. Thi s provi des approximately 1.5 feet of freeboard with the dam crest raised to elevation 6385.0. There is 1 i ttl e attenuati on of the PMF i nfl ow peak di scharge of 37,387 cfs. The computed peak outflow discharge is 36,600 cfs. - 40 -