CIV E 530 - OPEN-CHANNEL HYDRAULICS SPRING 2007 HOMEWORK No. 9 (50%) Determine the crest elevation and the shape of an overflow-spillway section having a vertical upstream face and a crest length of 250 ft. The design discharge is 75,000 cfs. The upstream water surface at design discharge is at Elev. 800 ft, and the average channel floor is at Elev. 650. (See Fig. 14-5 of text for reference). Plot the overflow-spillway section to an appropriate scale using AutoCAD. (50%) An emergency overflow spillway is being considered for the East Demerera Water Conservancy, in Guyana, to safeguard the integrity of the dam under conditions of climate change. Determine the length of the spillway required to pass the Probable Maximum Flood. Assume that the existing relief sluices are inoperable due to high tailwater during floods. The following data is applicable: 10,000-yr 1-day precipitation:   428 mm. Hydrologic abstraction:   13 mm. Contributing drainage area:   582 km2. Time base of the flood hydrograph:   4 days. Dam crest elevation:   18.288 m Spillway crest elevation:   17.526 m Freeboard:   0.3 m Weir discharge coefficient:   1.4 For simplicity, assume a triangular-shaped flood hydrograph. Use all the freeboard to contain the 10,000-yr flood.