WSP02105

• File Number: 8200.765
• Description: White River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 5/1/1986
• Author: Morrison-Knudsen
• Title: White River Geotechnical Study - Final Report - Volume I
• Water Supply Pro - Doc Type: Report/Study

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cost per acre-foot at the three storage capacities considered was fairly
constant, ranging from a high of $787/acre-feet for the 20,000 acre-foot
alternative to $758/acre-feet at the 60,000 acre-foot capacity. These storage
costs, however, do not compare favoraba1y to the cost per acre-foot of storage
at any of the other sites. The most expensive 50,000 acre-foot alternative
was the RCG dam at Veatch Gulch at $704/acre-feet or eight percent less than
the 60,000 acre-foot alternative at Lake Avery. The most economical 50,000
acre-foot reservoir was the RGG dam at Warner Point at $469/acre-feet or 62
percent less expensive than the Avery alternative.

Warner Point Dam
The most significant finding of the geotechnical investigation at the Warner
Point damsite was that the landslides on the left abutment are surficial,
extendin9 to 50 feet in depth and do not appear to affect the feasibility of
the project. The slide material would have to be completely removed to
provide an adequate foundation for any dam design.

The alluvial gravel in the valley bottom is thicker than had been previously
expected. The depth to bedrock ranges from 50 to 75 feet below the valley
floor. Thi s s i gni fi cant1y affects the economi cs of the proj ect, especi ally
the RGG alternative.

The upper bedrock zone underlying the left abutment consists of a sequence of
thi ck hard sandstone 1 ayers separated by thi n weathered si ltstone beds to a
depth of 75 feet. The zone has been characteri zed as weathered rock by the
seismic refraction survey, but in reality the majority of the rock is sound
except for the weathered zones that dip about 150 toward the river. For the
design and cost estimate of this report, the weathered rock was assumed to be
an adequate foundati on for the embankment dam, but unacceptab1 e for the RCG
alternatives. Any further geotechnical investigation at the Warner Point site
would have to detennine the continuity and strength of the weathered beds by
sampling and testing. A detailed stability analysis of the embankment or
gravity dam desi gn wou1 d be necessary. It can be conc1 uded from the present
subsurface investigation, however, that a suitable foundation for either an
embankment or gravity dam exi sts at a reasonab1 e depth at the Warner Poi nt
site.

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