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Land Use or <br />Surface Characteristics <br />Percentage <br />Imperviousness <br />Business: <br />Commercial areas <br />95 <br />Neighborhood areas <br />85 <br />Residential: <br />Single- family <br />* <br />Multi-unit (detached) <br />60 <br />Multi-unit (attached) <br />75 <br />Half -acre lot or larger <br />* <br />Apartments <br />80 <br />Industrial: <br />Light areas <br />80 <br />Heavy areas <br />90 <br />Parks, cemeteries <br />5 <br />Playgrounds <br />10 <br />Schools <br />50 <br />Railroad yard areas <br />15 <br />Undeveloped Areas: <br />Historic flow analysis <br />2 <br />Greenbelts, agricultural <br />2 <br />Off -site flow analysis <br />(when land use not defined) <br />45 <br />Streets: <br />Paved <br />100 <br />Gravel (packed) <br />40 <br />Drive and walks <br />90 <br />Roofs <br />90 <br />Lawns, sandy soil <br />0 <br />Lawns, clayey soil <br />0 <br />DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF <br />Table RO -3— Recommended Percentage Imperviousness Values <br />* See Figures RO -3 through RO -5 for percentage imperviousness. <br />C A = K + (1.311 – 1.44i +1.135i – 0.12 ) for CA >_ 0, otherwise CA 0 (RO - 6) <br />C CD = KCD + ( 0.858i 3 — 0.786i + 0.774i + 0.04) (RO - 7) <br />C B = (C + Co9V 2 <br />2007 -01 RO -9 <br />Urban Drainage and Flood Control District <br />