PROJ00345

• Contract/PO #: C153330
• Contractor Name: Upper Yampa Water Conservancy District
• Contract Type: Loan
• Water District: 0
• County: Routt
• Bill Number: SB 77-35
• Loan Projects - Doc Type: Feasibility Study

I

I

blockage of the spillway and outlet works or even failure of the dam due to

overtopping. Minor sloughing and erosion due to the combined effects of

I

wave action and rapid drawdown (which it is understood could be ~n the order

of 10 feet per day) will certainly occur during initial reservoir operation.

I

As the shoreline will stabilize normally with time, this temporary condition

I

is assumed to be acceptable.

Borrow Area A. The only portion of the future shoreline which would

I

appear to have significant slide potential is in the vicinity of Borrow Area A.

Existing slopes in that area are as steep as 2:1 within the reservoir fluctu-

I

ation zone, based upon field observation and map study. If not flattened by

I

excavation, these slopes will be adversely affected by drawdown, the high

water table during runoff, and the buoying effect of the reservoir. Under

I

these conditions,- the potential could exist for a dangerous slide, consider-
/ .

ing the elevation, orientation, and proximity of the slope to the dam and

I

spillway.

I

Without stabilizing excavation, the volume of such a slide could con-

ceivably be on the order of one million cubic yards in volume. To obtain a

I

"feel" for the possible consequences of such a slide, one might assume that

this volume moved from entirely above the reservoir level to a completely

I

submerged position near the upstream toe of the dam. The displaced reservoir

I

water, being roughly that of the soil bulk volume, would be some 600 A-feet.

Assuming the reservoir to be at spillway crest elevation prior to the slide,

I

the level would rise approximately three feet, leaving approximately 12 feet

of freeboard, It ~ould appear from these rough calculations that a gradual

I

slide would not cause overtopping of the dam, particularly if we take spill-

I

,way flow into account, A sudden slide could be capable of causing severe

waves but the probability of waves exceeding 12 feet in height would seem

I

very remote. On the other hand, the potential for a slide which could plug

the outlet works intake and at least partially block the spillway approach

I