Hydrology: The evaporation rate from the surface of a 3700 acre lake is 110 acre

Question

Hydrology: The evaporation rate from the surface of a 3700 acre lake is 110 acre-ft/day. Determine the depth change (feet) in the lake during a 365-day year if the inflow to the lake is 21.9 cfs. Is the change in lake depth an decrease or an increase? <1 acre-ft = 43,560 ft^3> Hydrology: The evaporation rate from the surface of a 3700 acre lake is 110 acre-ft/day. Determine the depth change (feet) in the lake during a 365-day year if the inflow to the lake is 21.9 cfs. Is the change in lake depth an decrease or an increase? <1 acre-ft = 43,560 ft^3>

Explanation / Answer

Area of lake = 3700 acres =3700*43560 ft^2 = 1.6117*10^8 ft^2

The evaporation rate = 110 acre-ft/day =110* 43,560 ft^3/day =4791600 ft^3/day = 4791600 *365 ft^3/yr

= 1748934000 ft^3/yr

The inflow to the lake = 21.9 ft^3/s = 21.9* 365*24*60*60 ft^3/yr= 690638400 ft^3/yr

Change in volume of lake in one year = 690638400 ft^3/yr - 1748934000 ft^3/yr

= -1058295600 ft^3

Depth change (feet) in the lake during a 365-day year = Change in volume of lake in one year / Area of lake

= -1058295600 ft^3/(1.6117*10^8 ft^2)

= - 6.57 ft

So the lake depth is decreasing.  

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