PERMFILE118993

• Permit No: C1980006A
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: DRAINAGE & SEDIMENT CONTROL PLAN
• Section_Exhibit Name: EXHIBIT 42
• Media Type: D
• Archive: Yes

Where: V velocity (fps)
S - slope (X)
Curve Number. CN
The runoff curve number (CN) is a factor relating the amount of rainfall
to the amount of runoff for a given area. It is dependent upon the
infiltration characteristics of soil types and the type and amount of
vegetation.
Curve numbers were obtained from Procedures for Determining Peak Flows in
Colorado and Technical Release No. 55, (USDA-SCS, 1980). Based on soil
type and vegetation cover, curve numbers were calculated for disturbed
considerations as follows:
Undisturbed - natural slope, soil, and vegetation
Soil Type: Predominately G
Vegetation Cover: 39X
Vegetation Type: Sage-grass
• CN: 69 (from Figure 23-12, Hydrologic Soil Cover complex 8
Associated Curve Numbers)
Disturbed - pits, stockpiles, etc.
Soil Type: D (worst case)
Vegetation Cover: 0%
CN: 90 (from Figure 23-12, Hydrologic Soil Cover Complex 8
Associated Curve Numbers)
81 Reclaimed - Area reclaimed in 1981
Soil Type: Predominately C (Coalmont)
Vegetation Cover: 43.2% (1991 Reclamation Report)
Vegetation Type: Sage - Grass
CN: 68 (from Figure 23-12, Hydrologic Soil Cover Complex and
Associated Curve Numbers.)
83 Reclaimed - Areas reclaimed in 1983
Soil Type: Predominately C (Coalmont)
Vegetation Cover: 52.6% (1991 Reclamation Report)
Vegetation Type: Sage - Grass
CN: 64 (From Figure 23-12 Hydrologic Soil Cover Complex and
Associated Curve Numbers)
23-64R Revised - August, 1991