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K <br />City Building inspection Department <br />September 12, 1979 <br />page 4 <br />RETENTION` DCflN'fION SYSTEM #3 at GRAPI[IC ARTS BUILDING <br />Post development Areas <br />8,773 <br />sq.ft. <br />New Roof <br />Area <br />4,OB5 <br />Existing <br />Rooi or Paving <br />4,200 <br />Gxistiny <br />Road <br />_ •3S <br />438 <br />Existing <br />Sidewalk <br />1,004 <br />New sidewalk —� <br />900 <br />Existing <br />(,ravel C <br />.7 <br />4 535 <br />sq.ft. <br />Grass <br />Total <br />Effective C <br />= .4 <br />m' .84 <br />Pro Development Areas <br />2,200 sq.ft. Existing caravel C .7 <br />920 " Existing sidewalk <br />4,205 " Existing Roof or Paving C = .95 <br />4,200 Existing Road <br />12,460 Grass C .4 <br />23,985 sq.ft. Total Effective C .64 <br />esign Storm <br />Pre development frequency 1 in 10 years <br />Post Development frequency 1 in 25 years <br />Duration 20 minutes <br />Intensity Pre Development 1.3 in./hr. <br />Intensity Poet Development 1.6 in./hr. <br />Pre pevelo went Deei n Runoff: <br />—P.-------JR2u -- <br />.64(133)(T7)23,985 - .64(666) - 554 CPT <br />Post Development Design Runoff: <br />.84(1T-) (17) 23,985 a .84(1066) = 695 C?T <br />Runoff Differential = 341 CFT <br />Orifice Opaning: <br />Diameter = 2-3/4" 23 985 <br />Discharge = .64(1.3) ,+- 1 .46 CFS <br />Head - 4,66 <br />A = _ .46 t -_.46 a :46 - .042 ft.2 <br />.63 64.4(4.66) .63(17.32) 10.9 <br />D 2 .115(2) - .1I1 :'.78" 1 one 2-3/4" of <br />it <br />