CIV E 530 - OPEN-CHANNEL HYDRAULICS
FALL 2008
HOMEWORK No. 14
- A 450-ac watershed is above a proposed flood-water retaining structure.
The watershed is divided into two subwatersheds, the first one of 205 ac, and the second one of 245 ac.
The characteristics are: (1) pasture (weeds), 75% canopy cover, 20% ground cover, Shelby loam, 8% slopes and 200 ft long;
(2) pasture (tall grass), 50% canopy cover, 60% ground cover, Mexico silt loam, 12% slopes, 100 ft long. Assume R = 200.
Use ONLINE USLE2 to calculate the watershed soil loss.
- Use ONLINE SHIELDS to
determine whether a particle of 3 mm diameter is at rest under a 0.8 m flow depth with a channel slope equal to 0.00025.
Assume T = 17oC. Under what flow depth (with accuracy to the cm) will the particle start to move?
- Use ONLINE COLBY to calculate the discharge of sands by the
Colby 1964 method given the following flow data: mean velocity = 3 fps, mean flow depth = 5 ft, channel width = 80 ft,
water temperature = 70oF, bed material size = 0.4 mm, and wash load concentration = 500 ppm.
- Use ONLINE RESERVOIR LIFE to calculate the design life of a reservoir, given the following data:
reservoir capacity 45 million cubic meters, catchment area 725 km2, mean annual runoff at the site 220 mm.
Assume fine grained sediment deposits with specific weight of 1400 kg/m3.
Determine how long will it take for the reservoir to lose 20%, 80% and 100% of its storage volume.
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