CIV E 530 - OPEN-CHANNEL HYDRAULICS FALL 2010 HOMEWORK No. 13 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.