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VISION CONSTRUC,'TION COMPANY <br />(�ENFRAL CUNTRACTQR <br />October 3, 1977 <br />Mr. Virgil Scott <br />Scott's Drywall <br />6308 - 212th Ave. S.W. <br />Lynnwood, Washington 9A036 <br />North Shorn Construction <br />R6: Storm retension for apartment complex <br />� <br />,, �n _ . ' ,. i�. <br />� <br />Assume: time of concentration = 10 minutes <br />so the rainfall intensity = 1.85 (Everett, 10 year, 10 minutec) <br />Undeveloped Land <br />Q = CIA = (.3) (1.85) (16,000) _ .20 cfs <br />43560 <br />Developed Project <br />Roofed arca = 4264 sq. ft. (c =.9) <br />Landscaped area = 6975 sq. ft. (c =.3) <br />Parking area = 4761 sq. ft. (c =.9) <br />Q' _ (.9) (1.85) (42G4 + 4761) + (.3) <br />43560 <br />(1.85) (G975) = 0.43 cfs <br />435G0 <br />0 Q = + 0.23 cfs <br />for 10 minutes storm - 138 cf minimum to store on site <br />Assume: perk rate of 15 minutes, so all runoff must be stored for duration <br />of storm. <br />Drainage Zonr �!1 - parking, paved access <br />storage required =(.9) (1.85) (9800) (60 sec.) (10 min.) - 110 cf <br />43560 <br />Use 8" perf pipe in l�e" washed gravcl, laid level <br />Storage volume per lin. foot = <br />Vol. pine + Vol. gravel voids <br />Vol pipe = .35 cf/f. <br />Vol gravel = (2') (.5') (.2 voids) _ .2 cf/f <br />Total = 0.55 cf/f <br />u15-116��� AVE. N.E., SU1TE �7U, BELLEVUE, WASH. ri800a PHONE 4b3 0483 <br />� <br />� <br />