2015-09-09_PERMIT FILE - C1981019A ‎(16)‎

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 9/9/2015
• 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), Continued
Runoff Curve Numbers for Cultivated Agricultural Land'
Cover Type Treatmentz Hydrologic A B C D
Condition3
Fallow Bare soil
77
86
91
94
Crop residue Poor
76
85
90
93
cover (CR) Good
74
83
88
90
Row Crops Straight row (SR) Poor
72
81
88
91
Good
67
78
85
89
S R + C R Poor
71
80
87
90
Good
64
75
82
85
Contoured (C) Poor
70
79
84
88
Good
65
75
82
86
C + CR Poor
69
78
83
87
Good
64
74
81
85
Contoured & terraced (C &T) Poor
66
74
80
82
Good
62
71
78
81
C &T + CR Poor
65
73
79
81
Good
61
70
77
80
Small grain SR Poor
65
76
84
88
Good
63
75
83
87
SR +CR Poor
64
75
83
86
Good
60
72
80
84
C Poor
63
74
82
85
Good
61
73
81
84
C + CR Poor
62
73
81
84
Good
60
72
80
83
C &T Poor
61
72
79
82
Good
59
70
78
81
C &T + CR Poor
60
71
78
81
Good
58
69
77
80
Close- seeded SR Poor
66
77
85
89
or broadcast Good
58
72
81
85
Legumes or C Poor
64
75
83
85
Rotation Good
55
69
78
83
Meadow C &T Poor
63
73
80
83
Good
51
67
76
80
Notes: ' Values are for average runoff condition, and 18 = 0 2S
z Crop residue cover applies only if residue is on at least 5 percent of the surface throughout
the year.
3 Hydrologic condition is based on a combination of factors affecting
infiltration and runoff-
density
and canopy of vegetative areas, amount of year -round cover, amount
of grass or closed-
seeded
legumes
in rotations, percent of residue cover on land surface (good > 20 percent), and
degree of roughness
Poor: Factors impair infiltration and tend to increase runoff.
Good: Factors encourage average and better infiltration and tend to
decrease runoff.
Exhibit 7 Page 13 Revision Date: 3/18/13
Revision No.: TR -95