PS 2 Examples Even Year


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UNIVERSITY OF CALIFORNIA, LOS ANGELES Civil and Environmental Engineering Department CEE 153 Introduction to Environmental Engineering Science Example Problems for Problem Set # 2 _____________________________________________________________________________ 1. A storage reservoir is to be built to store a river flow Q R and to supply a steady flow Q D = 10 8 m 3 /year to a town with a population of 100,000 people and an irrigation project with a total land area A = 10 8 m 2 . m s The town has a per capita water demand of 200 m 3 /person/year. The annual precipitation and evaporation from the irrigation area are estimated to be P = 0.5 m and E = 1.0 m, respectively. In addition, the irrigation project leaches a mass flow of dissolved salts m s = 10 7 kg/year from the soil. Assuming that the salt concentration in the water leaving the reservoir is negligible, will the flow from the reservoir Q D = 10 8 m 3 /year be sufficient to provide the town the needed water, to water the crops, and to insure that the concentration of dissolved salts in the downstream river c s will be less than the maximum drinking water standard which is 500 mg/L? [yes - the maximum possible need for water, assuming all uses are consumptive, is 9 × 10 7 m 3 /yr] 2. A country with a population of 500,000 people has a total land area of 10 4 km 2 . The annual freshwater runoff available for use is 10 9 m 3 , which is 20% of the total annual rainfall: a) Is the annual rainfall in this country more or less than the global average? [0.5 m/yr is half the global average] b) Is this country short of water? [2000 m 3 /person-year - not water stressed]
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3. A sewage treatment plant discharges tertiary effluent into the Los Angeles River. The effluent flow is Q e = 4 m 3 /sec and the effluent nitrogen mass flow is m N = 8 × 10 4 mg/sec (as N not a compound). The ambient river flow upstream from the plant is Q a = 1 m 3 /sec, and the ambient nitrogen concentration is c a = 0. The cross-sectional area of the river is A
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