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1 21 <br /> Orange Grove <br /> Storm Water Plan <br /> Page 2 <br /> I.S. total for 12 lots <br /> I.S. total for road 21,640 S.F. <br /> 2 <br /> I.S. TOTAL, FOR SUBDIVISION 87,696 S.F. <br /> S.F. <br /> Total Impervious Surfaces allowed at 12% = 184,782 S.F. <br /> *The total build-out will only result in use of 47% of allotted impervious <br /> surface coverage. <br /> The first 4" of rainfall will generate a volume of 3683 cu. ft. of storm water <br /> from the total impervious surfaces. (Total I.S. X .042') <br /> (A) Road ditch/swale effective retention within R/Ws;2 (6') effective width of <br /> 13' design width X 1" depth control height with gradient = 17,760 S.F. X <br /> .084' = 1492 cu. ft. <br /> (B) Two grassed wales as easements along lots 19 and 22;(2)12' X (420' + 570'); <br /> 5.5' effective width X 990' length = 5445; 5445 x .5" depth (.042) = 229 cu. ft. <br /> (C) Two 50' X 12' x 6 ' retention ponds; 3600 cu. ft. X 2 = 7200 cu. ft. <br /> CONCLUSIONS' <br /> USIONS <br /> - Total constructed infiltration = 1721 cu. ft. rainfall; <br /> - Total constructed retention = 7200 cu. ft. rainfall; <br /> - 46% of 4" rainfall will percolate naturally into soil along man-made devices; <br /> - 195% of the 4" and almost a full 1" of rainfall could be retained in the swale/ <br /> pond system. The extra freeboard is needed due to often neglected yearly maintenance/ <br /> cleanout schedules. <br /> • <br />