Measurement of changes in volume of water in an evaporation pan is a standard technique for estimating potential evapotranspiration. US Class A evaporation pans are cylindrical with the following dimensions: depth = 254 mm (10 in) and diameter 1219.2 mm (4 ft). (a) Calculate the cross-sectional area (m2) of a US Class A evaporation pan through which inflows and outflows of water can pass. (Answer: A = 1.17m2) (b) Initially the pan contained 233.5 litres of water, calculate the depth of water in the pan. After 24hours with no precipitation, the pan was checked and the volume of the water in the pan was determined to be 228 litres. Calculate the average evaporation rate (mm/day) from the pan. (Answer: E = 4.7mm/day) (c)The pan was refilled back to 233.5 litres of water and left in the field for another 24 hours. During this period, rain fell at a constant intensity of 5.5 mm/h for a 3-hour period. After 24 hours, the volume of the pan was 250.7 litres. Calculate the evaporation from the pan for this period. (Answer: E = 1.8mm/day)
Measurement of changes in volume of water in an evaporation pan is a standard technique for estimating potential evapotranspiration. US Class A evaporation pans are cylindrical with the following dimensions: depth = 254 mm (10 in) and diameter 1219.2 mm (4 ft).
(a) Calculate the cross-sectional area (m2) of a US Class A evaporation pan through which inflows and outflows of water can pass. (Answer: A = 1.17m2)
(b) Initially the pan contained 233.5 litres of water, calculate the depth of water in the pan. After 24hours with no precipitation, the pan was checked and the volume of the water in the pan was determined to be 228 litres. Calculate the average evaporation rate (mm/day) from the pan. (Answer: E = 4.7mm/day)
(c)The pan was refilled back to 233.5 litres of water and left in the field for another 24 hours. During this period, rain fell at a constant intensity of 5.5 mm/h for a 3-hour period. After 24 hours, the volume of the pan was 250.7 litres. Calculate the evaporation from the pan for this period. (Answer: E = 1.8mm/day)
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