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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 + Qin– Qout– E – G Assume groundwater, G = 0 Let A = lake surface area, acre ∆S = (P – E) + (Qin– Qout)∆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)(ft3/s)(86400s/d)(31 d)(acre/43560ft2) 530 = -0.6A + 615 0.6A = 85 A = 142 acres Surface Inflow, QinSurface Outflow, QoutPrecipitation, PEvaporation, EG (assumed negligible)
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