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DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF <br />Table RO-3=Recommended Percentage Imperviousness Values <br />Land Use or <br />Surface Characteristics Percentage <br />Imperviousness <br />Business: <br />Commercial areas 95 <br />Neighborhood areas 85 <br />Residential: <br />Single-family <br />Multi-unit (detached) 60 <br />Multi-unit (attached) 75 <br />Half-acre lot or larger <br />Apartments 80 <br />Industrial <br />Light areas 80 <br />Heavy areas 90 <br />Parks, cemeteries 5 <br />Playgrounds 10 <br />Schools 50 <br />Railroad yard areas 15 <br />Undeveloped Areas: <br />Historic flow analysis 2 <br />Greenbelts, agricultural 2 <br />Off-site flow analysis <br />(when land use not defined), 45 <br />Streets'. <br />Paved 100 <br />Gravel (packed) 40 <br />Drive and walks 90 <br />Roofs 90 <br />Lawns, sandy soil 0 <br />Lawns, clayey soil 0 <br />* See`Figures RO-3 through RO-5 for percentage imperviousness <br />Based,in part on the data collected by the District since 1969, an empirical relationship between C and <br />the percentage imperviousness for various storm return periods was developed. Thus, values for C can <br />bedetermined using the following equations (Urbonas, Guo and Tucker 1990). <br />CA K , + (1.3 Yi3 -1.4412 + 1.135i - 0.12) for CA ? 0, otherwise CA = 0 (RO-6) <br />0612002 RO-9 <br />Urban Drainage and Flood Control District <br />