CIV E 530 - OPEN-CHANNEL HYDRAULICS
SPRING 2008
HOMEWORK No. 9

  1. An emergency spillway is being considered for the East Demerera Water Conservancy, in Guyana, to safeguard the integrity of the dam under conditions of climate change. Assume that the existing relief sluices would be inoperable during a major flood due high tailwater. Determine the length of the free-overflow spillway required to pass the Probable Maximum Flood. 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

    • Embankment crest elevation:   18.288 m

    • Spillway crest elevation:   17.526 m

    • Freeboard:   0.3 m

    • Weir discharge coefficient:   1.45

    For simplicity, assume a triangular-shaped flood hydrograph. Use all the freeboard to contain the 10,000-yr flood.

  2. Use ONLINE OGEE RATING to determine the rating for an ogee overflow spillway with length L = 25 m, design head H = 1 m, [spillway] crest elevation = 1250 m, river bed elevation = 1230 m, and freeboard F = 0.5 m. What should be the dam crest elevation to pass the Probable Maximum Flood of 130 m3/s?

  3. Using ONLINE CHANNEL 12, find the energy loss through a hydraulic jump when the discharge is q = 20 cfs/ft and the upstream flow depth is y1 = 1 ft.

  4. Using ONLINE CHANNEL 16, find the sequent depths through a hydraulic jump when the discharge is q = 20 cfs/ft and the energy loss is ΔE = 2.4 ft.