Test 1 Precip-Water Balance 2018_solutions.pdf

Test 1 Precip-Water Balance 2018_solutions.pdf - CE 304...

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CE 304 Water Resources Engineering Test 1 Precipitation, Water Balance, Watersheds Solutions Problem #1 During the month of July, a lake had a mean inflow of 88 cfs. The outflow was 78 cfs. The increase in stored lake volume was 530 acre-ft. Precipitation during the same month was 9.8 in, while evaporation was 16.5 in. a) Draw a schematic of the lake’s water balance. b) What is the surface area of the lake? State any assumptions. Clearly write out full unit conversions. Answer with appropriate significant digits. A detailed step-by-step procedure on how to think through the solution is posted under a separate file. S/ t = P + Q in – Q out – E – G Assume groundwater, G = 0 Let A = lake surface area, acre S = (P – E) + (Q in – Q out ) t P, E already in units for the whole month t = 31 days (530 acre-ft) = (9.8-16.5 in)(ft/12 in) (A) + (88-78)(ft 3 /s)(86400s/d)(31 d)(acre/43560ft 2 ) 530 = -0.6A + 615 0.6A = 85 A = 142 acres Surface Inflow, Q in Surface Outflow, Q out Precipitation, P Evaporation, E G (assumed negligible)
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