The Dalles Dam Fish Guidance System
Geotechnical Exploration | Dam Project
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Project Description
The Dalles Dam is a hydroelectric dam located on the Columbia River 2 miles east of The Dalles, Oregon. The US Army Corps of Engineers planned to install a fish guidance system in the forebay of the dam to prevent fish from entering the water intake. The purpose of the project was to contribute to an environmentally friendly practice while simultaneously ensuring intake water quality. Water depths in the forebay ranged from 30 to 105 feet, where foundation conditions were mapped in order to locate anchor points for the proposed guidance system.
Team Members
US Army Corps of Engineers, Cornforth Consultants Inc., Crux Subsurface Inc.
Crux’s Role
The project involved drilling in water depths up to 105 feet and with currents of up to 3 feet per second. One third of the boreholes were located in active shipping lanes and water level fluctuations of up to 5 feet per setup were encountered. Permissible tolerance for borehole location was +/- 5 feet.
Crux designed and assembled a 40-foot by 18-foot barge from which drilling operations were conducted. The barge anchoring system included four 6,000-lb electric winches, each with a spool capacity of 500 feet of 3/8-inch steel cable. Anchor cables and winches were located below the work deck, which resulted in an open, uncluttered work area. Due to the strong current and to provide additional support to the free-length portion of the drill string, technologies to minimize the drift of the drill string were integrated into the barge design.
Crux-designed technology and methodology insured the verticality and stability of the free length of the drill string above mudline. HWT casing was advanced into competent rock, and HQ core was recovered for a further 40 feet. Packer testing and Crux Oriented Borehole Logging (COBL) optical televiewer surveys were also conducted in most boreholes.
Difficult Access
Crux’s 40-foot barge was utilized to access boring locations. The barge was maneuvered upstream of desired borehole locations with a support boat, upstream anchors were set, and the barge drifted downstream into the vicinity of the borehole. The support boat then set the downstream anchors and adjustments of the anchor winches allowed for movement of the barge to the exact desired GPS coordinates.
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