PERMFILE134290

• Permit No: C1981038
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: VOLUME 4-SURFACE WATER APPENDIX- EAST ROATCAP CREEK
• Media Type: D
• Archive: No

• tributary to the North Fork of the Gunnison River. The watershed
is located on the U.S.G.S. "Gray Reservoir, Colorado" 7 1/2
minute quadrangle.
East Roatcap Creek is the only defined drainage affecting
the proposed site for the new portal. It is an ephemeral stream
draining in a southerly direction with its headwaters originating
at High Park. The watershed is densely vegetated with shrubs in
the lower elevations and forested in the upper elevations.
The drainage area for East Roatcap Creek was measured at two
locations. An upstream site at point DA-1 North located near the
new flume (SW-6A) has a drainage area of approximately 3.7 mil
(2,368 acres). A site at the entrance to the culvert beneath the
proposed portal bench (point DA-2 South) located approximately
1,200 ft. downstream of SW-6A has a drainage area of
approximately 3.8 mil (2,432 acres). The location of points DA-1
and DA-2 are shown on Figure H-4. East Roatcap Creek joins
Roatcap Creek approximately 5,500 ft. downstream of SW-6A.
The Overland Ditch flows through the upper portion of the
drainage area from east to west at an elevation of approximately
9,250 ft. The area above the Overland Ditch was included in the
watershed areas.
• Watershed elevations range from 9,600 ft. in the headwaters
to 7,120 ft. at the proposed portal bench culvert entrance and
approximately 5,580 ft. at the confluence with Roatcap Creek.
The length of the watershed at SW-6A is 16,240 ft. Mean basin
slopes of 12~ were calculated for both watershed locations. Peak
flows were estimated from basin characteristics for both
watersheds using two methods.
"Estimation of Natural Streamflow Characteristics in Western
Colorado", a U.S. Geological Survey publication (Kircher, 1985),
will be referred to as Method 1. This method uses a regression
analysis to predict peak flows based on U.S.G.S. stream flow data
from 141 stations located in mountainous areas in western
Colorado. Hydrologic parameters used in the estimation of peak
flows in this met)iod include watershed area, in mil, and mean
basin slope in feet/feet. Mean basin slope is measured between
two points along the main channel, one of which is located at 108
of the channel length and the other at 858 of the channel length.
Method 2, "Manual for Estimating Flood Characteristics of
Natural Flow Streams in Colorado" (TM-1), (McCain, 1976) is also
a regression analysis method based on U.S.G.S. stream flow data
from 111 stations in the mountainous areas in western Colorado.
The mountain regions used for both methods encompass the same
area. The regression equations are based on differing stations
• and periods of record. Hydrologic parameters used in the
estimation of peak flows in Method 2 include area, in mil, and
mean annual precipitation, in inches.
The East Roatcap watershed lies predominantly in the
2