PERMFILE70173

• Permit No: C1981039
• IBM Index Class Name: Permit File
• Doc Name: Slide Plan 10/4/90
• Section_Exhibit Name: Reclamation Project Binder
• Media Type: D
• Archive: No

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• Mr. Brent Anderson
Page Two
October 1, 1990
There is no evidence of recent movement in the scarp areas, and the=
drainage ditch at the toe is open. Comments from Rockcastle personnel
indicate that the ditch has not been cleaned for at least two years: The
slide shows no evidence of ongoing downslope movement.' ~"
While the slide is currently stable, there is always the possibility of
renewed movement if saturated soil conditions recur. This possibility is
inherent to the steep terrain which dominates the site. A number of
slides unrelated to road construction or other disturbance have been
observed in northwest Colorado on similar steep slope areas. While it is
not passible to completely prevent potential future movement as the
natural process of mass wasting is inevitable, measures can be taken to
minimize the potential for future movement and address concerns about long
term maintenance of the road. Four measures are examined conceptually.
These are:
• Diverting water around the head scarp
• Improving drainage at the toe of the slide
• Installing a toe buttress
• Annual inspections
• DIVERTING WATER AROUND THE HEAD SCARP
There are several areas around the head scarp where water could pool,
increasing infiltration to the base of the slide material. It would be
possible to divert water around the head scarp, thereby minimizing run-on
to the head scarp from upgradient areas. The field inspection
specifically addressed the question of installation of a drainage ditch
above the head scarp.
The vegetation above the slide is relatively dense and mature. In order
to install a diversion ditch above the slide it would be necessary to
first clear the heavy vegetation to provide for equipment access. Removal
of this vegetation would have the potential to significantly increase
runoff and erosion in the cleared area and could conceivably destabilize
the hillside, shifting the head scarp to the diversion ditch location.
In order to be effective, the ditch would need to flow to the east.
Examination of the hillside above the road between the curve and the
switchback at the bottom of the hill indicates a potential for surficial
instability along the entire stretch of road. Therefore, in order to
construct an upslope diversion ditch, the ditch would have to be at least
2,000 feet long discharging directly to a major drainage to the east.
There is no place along the haul road where this drainage could be routed
down the hillside into the haul road drainage ditch without significant
erosion. Even though there is considerable appeal in trying to divert
run-on from upslope areas, physical constraints of the"site, and the ~`
• condition of the hillside make this alternative unattractive._ "