CIV E 530 - OPEN-CHANNEL HYDRAULICS
FALL 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:   18 mm

    • Contributing drainage area:   582 km2

    • Time base of the flood hydrograph:   3 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 spillway with length L = 20 m, design head H = 2 m, spillway crest elevation = 1045 m, river bed elevation = 1000 m, and freeboard F = 1 m. Neglect the approach velocity. What should be the spillway length to pass the Probable Maximum Flood of 260 m3/s while taking all the freeboard?

  3. Use ONLINE CHANNEL 12 to determine the sequent depth y2 and energy loss ΔE through a hydraulic jump when the discharge is q = 16 cfs/ft and the upstream flow depth is y1 = 0.8 ft.

  4. Use ONLINE CHANNEL 16 to calculate the sequent depths through a hydraulic jump when the discharge is q = 16 cfs/ft and the energy loss is ΔE = 2.7 ft.