2009-06-23_PERMIT FILE - C1981019A

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 6/23/2009
• Section_Exhibit Name: Exhibit 07 Methodologies & Assumptions for Sedimentation Pond Design Evaluations
• Media Type: D
• Archive: Yes

Table 8 Curve Numbers Provided in the SEDCAD model (from National Engineering
Handbook (NEH-4) (USDA-SCS, 1985)
Runoff Curve Niimhere fnr I Irhan Areac
Cover Type and Hydrologic Condition Average Percent A B C D
Impervious Area
Open space (lawns, parks, golf courses,
cemeteries, etc.)
? Poor condition (grass cover < 50%) 68 79 86 89
? Fair condition (grass cover 50% to 75%) 49 69 79 84
? Good condition (grass cover> 75% 39 61 74 80
Paved parking lots, roofs, driveways, etc. 98 98 98 98
(excluding right-of-way)
Streets and roads:
? Paved; curbs and storm drains (excluding 98 98 98 98
right-of-way)
? Paved; open ditches (including right-of- 83 89 92 93
way)
? Gravel (including right-of-way) 76 85 89 91
? Dirt includin right-of-way) 72 82 87 89
Western desert urban areas:
? Natural desert landscaping (pervious areas 63 77 65 88
only)
? Artificial desert landscaping (impervious 96 96 96 96
weed barrier, desert shrub with 1- to 2-inch
sand or ravel mulch and basin borders
Urban districts:
? Commercial and business 85 89 92 94 95
? Industrial 72 81 88 91 93
Residential districts by average lot size:
? 1/8 acre or less (town houses) 65 77 85 90 92
? 1/4 acre 38 61 75 83 87
? 1/3 acre 30 57 72 81 86
? 1/2 acre 25 54 70 80 85
? 1 acre 20 51 68 79 84
? 2 acres 12 46 65 77 82
Developing urban areas:
Newly graded areas (pervious areas only, no 77 86 91 94
vegetation)
Notes: Values are for average runoff condition, and la = 0.2S.
The average percent impervious area shown was used to develop the composite RCNs.
Other assumptions are: impervious areas are directly connected to the drainage system , impervious areas
have a RCN of 98, and pervious areas are considered equivalent to open space in good hydrologic
condition.
Exhibit 7 Page 11 Revision Date: 6/19/09
Revision No.: TR-73