2009-01-07_PERMIT FILE - C1981022 ‎(5)‎

• Permit No: C1981022
• IBM Index Class Name: Permit File
• Doc Date: 1/7/2009
• Doc Name: Bear Creek Fan Site SAE
• Section_Exhibit Name: Exhibit 2.05-E3 Section 9h
• Media Type: D
• Archive: No

HYDROLOGIC DOCUMENTATION
SMALL r1REA EXEMPTION
BEAR CREEK FAN SITE - LAYDOWN AREA
The following calculations demonstrate the amount of silt fence or straw bales surface area required to adequately
handle the runoff from the Bear Creek Fan Site.
Runoff volume and peak discharge calculations were performed using the SEDCAD 4 computer model consistent
with the methodology previously discussed in this Exhibit. The sediment control structure was designed using the
pond routine in SEDCAD 4 to handle the peak discharge from a 10-year, 24-hour storm event. Length of the silt
fence and straw bales was determined from the topography of the site and from the necessary sediment storage to
comply with a settable solids limit of 0.5 ml/l. Input discharge rates for the Sedcad model were calculated from a
rate of 5.6 gpm/ft2 for straw bales and a rate of 10.0 gpm/ft2 for a silt fence. Printouts of the Sedcad designs for a
silt fence and a straw bale boundary are provided below.
1. H, drology Inputs
All hydrology inputs are shown on the SEDCAD computer printouts.
The CN numbers used for the SAE watershed were obtained from Procedures for Determining Peak
Flows, in Colorado and Technical Release No. 55 (USDA-SCS, 1986) and consistent with previously
approved hydrology reports. Based on the soil type and vegetation cover, curve numbers were determined
using Table 2-2a and 202d, USDA-SCS TR-55, for the following conditions:
Disturbed:
Soil Type:
Ground Cover:
Cover Type:
CN:
Area:
Undist<irbed:
Soil Type:
Ground Cover:
Cover Type:
CN:
Area:
2. Hydrology Results
C-D
Bare
Gravel Road
90
0.2 acres
C-D
Fair to Good
Oak-Aspen
57
0.5 acres
Peak Discharge -Silt Fence or Straw Bales 0.37 cfs
10-year, 24-hour event
3. Hydraulic Structure Inputs
Assumed Length of Silt Fence or Straw Bales G0.0 ft
Assumed Height of Silt Fence or Straw Bales 1.5 ft
Assumed Slope behind Silt Fence or Straw Bales 25.0