REV93703

• Permit No: M1973021
• IBM Index Class Name: Revision
• Doc Name: REGULAR 112 PERMIT APPLICATION FORM
• Type & Sequence: AM2
• Media Type: D
• Archive: No

t The facilities described as needed, either during or after the mining
operation, are in the nature of engineering recommendations and con-
ceptual designs. Because the operation will take place over many years
and conditions may arise which require modification to the drainage
1 plan, detailed designs of drainage structures are not suggested until
such time as the implementation program for the construction of the
facilities makes them necessary.
' HISTORIC CONDITION
' The Cooley Gravel Company's Morrison Ouarry is situated in Strain Gulch
in Sections 10 and 11, Township 5 South, Range 70 West of the 6th P.M.,
approximately 1-1/2 miles south of Morrison, Colorado. The location of
' the quarry and other pertinent features in the vicinity are shoran on
Figure 1. The studies mentioned above contain a detailed description of
the Strain Gulch basin and the effects of the Morrison Ouarry on its
' hydrologic characteristics. Cooley Gravel Company currently plans to
expand its gravel mining operation into two adjacent basins to the south
of the present quarry area, hereinafter referred to as Unnamed Culch "A"
and Unnamed Gulch "B". This report addresses the potential impacts of
the proposed quarry expansion on the hydrology of those basins.
The watershed of Unnamed Gulch A, a tributary of Turkey Creek, has an
area of approximately 0.21 square miles (132 acres) upstream of the
lower edge of the proposed quarry expansion. The quarry pit will be
enlarged to include an area of approximately 73 acres in [his basin.
' Unnamed Gulch B, also a tributary of Turkey Creek, has an area of
approximately 0.13 square miles (82 acres) above the proposed quarry
expansion. The enlarged quarry pit will include approximately 23 acres
1 in [his basin. Both basins have characteristically steep slopes with
relatively sparse vegetation, contributing to a naturally high runoff
rate during major storms.
Like Strain Culch, Unnamed Gulches A and B are intermittent streams with
a base flow only during the spring and early summer snowmelt runoff
periods. They are generally dry gulches during the summer and fall,
'' carrying only runoff from occasional short duration, high intensity
thunderstotas. The historic peak rate of flow in Gulch A at the lower
edge of the proposed quarry pit resulting from a 5-hour, 100-year storm
' is approximately 200 cfs. (This includes the runoff contribution from a
17 acre area, denoted "Area C" on the vicinity map, which has not
historically been included in Gulch A but which will contribute runoff
to the pit as a result of the avarry expansion.) The historic peak flow
in Gulch B at the lower edge of the proposed quarry pit resulting from a
6-hour, 100-year storm is approximately 130 cfs. Under historic con-
ditions, a flood of this magnitude would cause water to flow in this
' gulch approximately 1.4 feet deep.

2