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Table 8 Curve Numbers Provided in the SEDCAD model (from National Engineering <br />Handbook (NEH -4) (USDA -SCS, 1985) <br />Runoff Curve Numbers for Urban Areas <br />Cover Type and Hydrologic Condition Average Percent <br />A <br />B <br />C <br />D <br />Impervious Area <br />Open space (lawns, parks, golf courses, <br />cemeteries, etc ) <br />♦ Poor condition (grass cover < 50 %) <br />68 <br />79 <br />86 <br />89 <br />♦ Fair condition (grass cover 50% to 75 %) <br />49 <br />69 <br />79 <br />84 <br />♦ Good condition (grass cover > 75% <br />39 <br />61 <br />74 <br />80 <br />Paved parking lots, roofs, driveways, etc. <br />98 <br />98 <br />98 <br />98 <br />(excludin right-of-way) <br />Streets and roads: <br />♦ Paved; curbs and storm drains (excluding <br />98 <br />98 <br />98 <br />98 <br />right -of -way) <br />♦ Paved, open ditches (including right -of- <br />83 <br />89 <br />92 <br />93 <br />way) <br />♦ Gravel (including right -of -way) <br />76 <br />85 <br />89 <br />91 <br />♦ Dirt (including right-of-way) <br />72 <br />82 <br />87 <br />89 <br />Western desert urban areas: <br />♦ Natural desert landscaping (pervious areas <br />63 <br />77 <br />85 <br />88 <br />only) <br />♦ Artificial desert landscaping (impervious <br />96 <br />96 <br />96 <br />96 <br />weed barrier, desert shrub with 1- to 2 -inch <br />sand or gravel mulch and basin borders <br />Urban districts: <br />♦ Commercial and business 85 <br />89 <br />92 <br />94 <br />95 <br />♦ Industrial 72 <br />81 <br />88 <br />91 <br />93 <br />Residential districts by average lot size. <br />♦ 1/8 acre or less (town houses) 65 <br />77 <br />85 <br />90 <br />92 <br />♦ 114 acre 38 <br />61 <br />75 <br />83 <br />87 <br />♦ 1/3 acre 30 <br />57 <br />72 <br />81 <br />86 <br />112 acre 25 <br />54 <br />70 <br />80 <br />85 <br />♦ 1 acre 20 <br />51 <br />68 <br />79 <br />84 <br />♦ 2 acres 12 <br />46 <br />65 <br />77 <br />82 <br />Developing urban areas: <br />Newly graded areas (pervious areas only, no <br />77 <br />86 <br />91 <br />94 <br />ve etation <br />Notes: Values are for average runoff condition, and 1, = 0.25. <br />The average percent impervious area shown was used to develop the composite RCNs. <br />Other assumptions are: impervious areas are directly connected to the drainage system, <br />impervious <br />areas <br />have a RCN of 98, and pervious areas are considered equivalent to open space in good hydrologic <br />condition. <br />Exhibit 7 Page 12 Revision Date: 3/18/13 <br />Revision No.: TR -95 <br />