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Estimate the land area required for retention ponds <br /> Assume 3:1 side slopes <br /> Assume 2 feet free board when pond is full <br /> Assume 10 foot water depth <br /> Area D @ 1.55 acres <br /> Surface area full 67,518 ft2 <br /> Surface area empty 47,500 ft2 <br /> Average surface area 57,509 ft2 <br /> Volume 575,090 cu. feet <br /> 4,301,673 gallons <br /> Case III requires more land area <br /> Increase land area to 2.32 acres (move 100 feet to west) <br /> Surface area full 101,059 ft2 <br /> Surface area empty 91,000 ft2 <br /> Average surface area 96,030 ft2 <br /> Volume 960,296 cu. ft <br /> 7,183,014 gallons <br /> Actual land area required is somewhat less. <br /> Estimate annual volume of runoff hauled in a 20-year period <br /> .;ase I Average is zero. <br /> Assume 10 years no water is hauled. <br /> Every 5 years precipitation is 17.4 inches 4 events 2.8 inches <br /> Every 10 years precipitation is 19.5 inches 2 events 4.9 <br /> Every 20 years precipitation is 21.4 inches 1 event 6.8 <br /> Assume 3 additional events at half the 5 year 3 events 1.4 <br /> Total 15.9 inches <br /> Volume= 14,346161 gallons for 20 year period <br /> Annual average= 717,308 gallons <br /> Case II Same assumptions as Case I for calculating 20 ear volume <br /> Volume= 7,110,480 gallons for 20 year period <br /> Annual average= 355,524 gallons <br /> tCase II Haul runoff even in average year <br /> Annual average= 3,054,518 gallons <br /> FN: dtr/a:\WATERBAL.XLS Page 4 of 5 Printed:8/31/94 3:46 PM <br />