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0 <br />� <br />VISION C;�NSTRIJCTION C..,�VIPANY <br />(3ENERAL CONTRACTOR <br />_Octobcr 3, 1977 <br />Mr. Virgil Scott <br />Scott's Drywall <br />6308 - 212th Ave. 5.47. <br />Lynnwood, Washir.gton 96U36 <br />North Shore Construction <br />R6: Storm reten�ion for apartment complex <br />Assume: time of concentration = 10 minutes <br />so the zainfall intensity = 1.85 (Eve�ett, 10 year, 10 minutes) <br />Undeveloped Lanci <br />Q = CZA = (.3) (1.95) (16.000) _ .20 cfs <br />43560 <br />Developed Project <br />ttoofed azea = q264 sq. ft. (c =.9) <br />Landscaped atca = 6975 sq. ft. (c =.3) <br />Farking area = 47G1 sq, ft. (c =.9) <br />. . Q' _ (.9) (1.85) (A264 + 4761) �f� (.3) <br />43`_60 <br />(1.85) (6975! = 0.43 cfs <br />43560 <br />� Q = + �,�3 cfs � <br />for 10 minutes storm = 138 cf minimum to store on site <br />Assume: perk rat� of 15 minutes, so all runoff must be stored for duration <br />of storm. <br />Drainage 7.one �1 - parking, paved access - <br />storage re.quired = (.9) (1.85) (4800) (60 sec.) (10 min.) - 110 cf . <br />43560 <br />Use 8" p�rf pipe in 15" washed gravel, laid level <br />Storage vo?.ume per lin. foot = <br />Vol. pipe + Vol. qravel voids <br />Vol pipe = .35 cf/f. <br />vol gravel = (Z�) (,5�� (,2 voids) _ .2 cf/f <br />Total = 0.55 cf/f <br />676-110�h GVI:. N.�., 6UITF, t7E3, L�1•;LLEVUR, WAF.SL 08pp.y PIIONF. 45:1 048� <br />� <br />