A 18.8 [km 2 ] alpine watershed received 12 [meters] of snow last calendar year.

Question

A 18.8 [km2] alpine watershed received 12 [meters] of snow last calendar year. The ratio of snow depth to equivalent water depth is 10:1. At the beginning of the year the shallow soil mantle across the watershed is mostly saturated. The discharge from the basin averaged 0.4 [m3 s-1].

Precipitation = (12x0.1)x(18.8x106) = 22,560,000 [m3 yr-1]

Discharge = (0.4)x(60x60x24x365) = 12,614,400 [m3 yr-1]

Storage change is zero since soil begins at saturation and ends at saturation

Evaporation = Precipitation - discharge = 9,945,600 [m3 yr-1]

Divide by watershed area, evaporation = 0.53 [m yr-1]

What is the mean annual evaporation rate in [m yr-1] for the watershed?

Explanation / Answer

At the beginning of the year the shallow soil mantle across the watershed is mostly saturated. The discharge from the basin averaged 0.4 [m3 s-1].

Precipitation = (12x0.1)x(18.8x106) = 22,560,000 [m3 yr-1]

Discharge = (0.4)x(60x60x24x365) = 12,614,400 [m3 yr-1]

Storage change is zero since soil begins at saturation and ends at saturation

Evaporation = Precipitation - discharge = 9,945,600 [m3 yr-1]

Divide by watershed area, evaporation = 0.53 [m yr-1]

therefore 0.53 [m yr-1] is the mean annual evaporation rate in [m yr-1] for the watershed

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