Pond Water Evaluations

Rainfall supply projections as of 12/13/2019

Water Surface is 0.5 acres or approximately 21,800 SF

  • 21,800 SF at an average 3.5 foot depth = 648,500 gallons.
  • 21,800 x 0.08 = 1,744 CF or 14,800 gallons per inch of depth

Rough rainfall runoff area = 4.7 ac

A 1″ rain over 4.7 ac would be 139k gallons total. If only half runs to the pond then 69,500 gallons would add to the pond 69500/14800 or 4.7 inches.


Evaporation Rates

From NOAA Technical Report NWS 34 Mean Monthly, Seasonal, and Annual Pan Evaporation for the United States

All of the evaporation values in these tables represent estimates of expected evaporation occurring from a Class A pan …. The evaporation from shallow lakes and moist soils is generally classified by one of the following equivalent names: free water surface evaporation (FWS), lake evaporation (E1 ), or potential evapotranspiration (PE).

An estimate of FWS which is more accurate than that given by multiplying the pan value by 0.70, is obtained by multiplying the pan amount by the appropriate coefficient from map 4 of the evaporation atlas described earlier. [See analysis below.]

Analysis using data from NOAA Technical Report NWS 33 Evaporation Atlas for the Contiguous 48 United States Washington, D.C. June 1982

Pond Volume at 160,000 gallons/ft = 13,300 gallons/inch
From NWS 33 – Annual Class A Pan Avg. of 15 years Evaporation in Fairhope AL From Table 2, Inches 51
NWS 33 Map 4 coefficient for May-Oct0.76
Percent of Annual. NWS 33 Table 2 (1)Inches/Month76% adj for shallow pondsGallons EvaporatedPump hours at 20 GPM
Jan3.71.91.4           19,074                  16
Feb4.82.41.9           24,744                  21
Mar7.84.03.0           40,210                  34
Apr9.85.03.8           50,520                  42
May12.56.44.8           64,439                  54
Jun12.56.44.8           64,439                  54
Jul12.36.34.8           63,407                  53
Aug11.15.74.3           57,221                  48
Sep9.34.73.6           47,942                  40
Oct7.63.92.9           39,179                  33
Nov4.82.41.9           24,744                  21
Dec3.81.91.5           19,589                  16
51.038.8

(1) Class A Pan, Station in Fairhope 2NE, AL.

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