Overview

Vega Dam is near the Grand Mesa in western Colorado, about 10 miles east of the town of Collbran. The dam is a zoned, rolled earth and rockfill structure with a maximum height above foundation of 162 feet, a crest length of 2,100 feet, and a volume of 981,825 cubic yards of material. The outlet works is near the left abutment and consists of an intake structure, 5-foot diameter concrete pressure conduit, concrete gate chamber for a 3.5-foot-square high-pressure emergency gate, 8-foot-diameter concrete horseshoe conduit containing a 51-inch-diameter steel pipe, control house containing two 2.25-foot-square high-pressure control gates, concrete stilling basin, and an outlet channel which discharges into the Southside Canal.

Vega Reservoir has a surface area of about 900 acres, with a capacity of 33,800 acre-feet, and a shoreline of approximately 7 miles.

Geology

Collbran Project is located along the northeastern slope of Grand Mesa. The mesa is composed of horizontally bedded, tertiary rocks belonging to the Wasatch and Green River formations and capped by lave flow of Quaternary basalt. During Pleistocene times, sheet-like glaciers covered the mesa. Glacial scouring produced the many small mesa lakes and the heterogeneous deposits of glacial debris, which mantle a large part of the surface rock. These glacial deposits cover the lava in varying depths from one hundred to several hundred feet. The Vega Damsite is in an erosional narrows cut across the toe of a large fan. Overburden debris covers bedrock at the damsite to a depth of 135 feet, becoming progressively deeper to the south. The fan is composed of clayey silt containing basalt boulders. It is compact and seepage tests indicate that it is watertight. Even with a high water table, little or no slumping of side slopes has occurred, and other field evidence indicates good stability.

General

Dimensions

Hydraulics & Hydrology