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Estimate the land area required for retention ponds <br /> Assume 3A 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 57,5091ft2 <br /> Volume 575,090 cu. feet <br /> 4,301,673 allons <br /> Case III requires more land area _ <br /> Increase land area to 2.32 acres move 100 feet to west <br /> C Surface area full 101,059 ftz <br /> Surface area empty 91,000 ft2 <br /> Average surface area 96,030 ft2 <br /> L� Volume 960,296 cu. ft <br /> 7,183,014 gallons <br /> L _ 4 Actual land area re uired Is somewhat less. <br /> Estimate annual volume of runoff hauled In a 20-year period <br /> 3ase 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 6.6 <br /> Assume 3 additional events at half the 5 ear 3 events <br /> Total <br /> 15.9 inches <br /> Volume= 14,346;161 allons for 20 year period <br /> Annual average= 717,308 gallons <br /> r <br /> Case II Same assumptions as Case t for calculating 20 year volume <br /> Volume= 7,110,480 gallons for 20 yearperiod <br /> Annual average= 355,524 gallons <br /> Case 11 Haul runoff even in avera a year <br /> Annual average= 3,054,518 gallons <br /> 0 FN: dtr/a:\WATERBAL.XLS Page 4 of 5 Printed: 8/31/94 3:46 PM <br />