2023-04-19_PERMIT FILE - C1981010A ‎(14)‎

• Permit No: C1981010A
• IBM Index Class Name: Permit File
• Doc Date: 4/19/2023
• Doc Name: pages 4-172 to 4-222z
• Section_Exhibit Name: 4.8 Hydrologic Impacts
• Media Type: D
• Archive: Yes

Drainage Desiqn Example. An example drainage design calculation was conducted as follows. Curve
numbers and slopes for each area are determined by existing ground cover conditions and topography at
the time the drainage is deemed ready for construction. In this example the check dam and dozer basin
requirements for a 306 acre drainage are examined. The chart below gives the breakdown of sub parcels
by reclamation stage.
Acres
Curve Number
Slope
Weighted average curve numbers and slopes are calculated for the entire watershed. The weighted
average curve number for this example watershed is 82; the weighted average slope is 7.56%, rounded
up to 8%.
Based on the model in Appendix Q, Section 37, by Tom Peterson of Environmental Solutions, the number
of acres that can be accounted for per each check dam is calculated. This calculation is determined in
part by the storage capacity created by each check dam based on typical check dam construction
methods, the slope of the drainage channel, and the amount of detention required to meet velocity,
sediment, and effluent regulatory standards.
The charts below display the relationship of the aforementioned values in table 4.8-5a when applied to the
specific drainage conditions outlined in this example.
Curve Number, Acres per Check Dam, and Check Dams Required for 306
Subwatershed details
CN
Disturbed
Retopsoiled
and Seeded
1 year
growth
2 year
growth
125.0
80.0
45.0
56.0
87
86
80
67
6.4
9.3
8.4
7.0
Weighted average curve numbers and slopes are calculated for the entire watershed. The weighted
average curve number for this example watershed is 82; the weighted average slope is 7.56%, rounded
up to 8%.
Based on the model in Appendix Q, Section 37, by Tom Peterson of Environmental Solutions, the number
of acres that can be accounted for per each check dam is calculated. This calculation is determined in
part by the storage capacity created by each check dam based on typical check dam construction
methods, the slope of the drainage channel, and the amount of detention required to meet velocity,
sediment, and effluent regulatory standards.
The charts below display the relationship of the aforementioned values in table 4.8-5a when applied to the
specific drainage conditions outlined in this example.
Curve Number, Acres per Check Dam, and Check Dams Required for 306
Acre Drainage at 8% slope per Table 4.8-5a
CN
83
82
81
80
79
78
77
76
75
74
73
72
71
70
69
68
67
Acres
per
Check
5.92
7.54
9.15
10.77
12.38
14.00
19.60
25.20
30.80
36.40
42.00
47.60
57.08
66.56
76.04
85.52
95.00
Dam
Check
Dams
51.69
40.58
33.44
28.41
24.72
21.86
15.61
12.14
9.94
8.41
7.29
6.43
5.36
4.60
4.02
3.58
3.22
Req.
4-1831
Check Dams Required vs. CN
60O
50
o
& 40
E 30
a 20 1 NIL
- -
10
83 82 81 80 79 78 77 76 75 74 73 72 7170 69 68 67
Curve Number
Revision: N-0
*Pnroved•