Agenda - 06-17-1986 - Laserfiche WebLink

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06 • ORANGE GROVE STORM WATER PLAN OBJECTIVES: The lot layout for "Orange Grove" was done in such a way to maximize the following storm water objectives: ( 1) To establish large enough lots (avg. 2.78 ac.) in order to enhance natural assimilative capacities of the relatively slow soil percolation rates of 2"-6" per hour; (2) To situate lots such that excess rainfall will drain, through sheet flow, into catchment areas called grassed swales, that can absorb and retain the first 4 inch of rainfall during any given storm frequency event; (3) To allow for maximum use of both natural (oak-hickory-pine) overstory and planted herbaceous ground cover (fescue, rye, etc.). to encourage evapotrans- _. piration of the inFiltrated volume of water; (4) To use a combination of easily maintained engineered structures for storm water retention when such devices are rarely needed. Examples include catch basins, rock wiers, rock check dams and diffusers and two simple retention ponds with stand pipes as volume control tools. NATURAL FEATURES: ( 1) Soils - Five soil series exist on the 35.35 acre tract and are illustrated aithe attached table. The permeability of the first eight inches averages 2"-6" per hour for the good silt loam soils which comprises 73% of the tract. The underlying subsoil series peres about .6-1 .0" per hour and can still soak in the first flush of Z" of rainfall with relative efficiency. (2) Geologic Features - The slope of the site does not allow simple one to one calculations since it has a consistent gradient of 4-57 slope from North to South. Some rock outcroppings in the Tatum and Herndon soil groups compound the calculations. In some cases, rock fissures can help infiltrate surface runoff into underlying subsoils. End of the line retention ponds should not be located near these rock outcroppings in order to avoid potential contami- nation of ground water due to heavy head pressures. (3) Vegetation -- The relatively mature (45-60 years) timber with thick layers of leaf litter and Al layer humus also affords fast absorption of the first 4". The large lots allow for future residential use which will have accumulative impervious surfaces (IS) well below the allotted 12% zoning restrictions. ASSUMPTIONS FOR TYPICAL BUILDING: Average house footprint (40' X 45') 1800 S.F. Average 2 car garage footprint (24' X 32') 768 S.F. Average driveway dimension ( 100' X' 20') 2000 S.F. Sidewalk area/lot (50' X 4') 200 S.F. Patios ( 16' X 20') 320 S.F. IMPERVIOUS SURFACES/LOT 5088 S.F.