Caples Lake Dam Remediation

Syblon Reid was awarded an emergency design/build contract for modifications to Caples Lake Dam.

In partnership with GEI Consultants, Inc., the contract was awarded to provide support in developing plans to lower and store reservoir water, assist in obtaining resource agency permits, and replace two aging slide gates to restore the safety and operational reliability of the malfunctioning reservoir regulating gates in the outlet shaft system.

In order to gain access to the low level outlet tunnel, a cofferdam system needed to be installed to not only provide a means to access the gates, but also retain adequate amounts of stored water to maintain minimum stream flows below the dam. Once the reservoir was brought down to minimum levels, two 8-foot high water filled bladder dams were installed. Not only are these dams extremely environmentally friendly, they are quick to install, taking only one day for the installation. Stream flow was obtained with 3,200 feet of bypass piping from the cofferdams to the downstream side of Cables Lake Dam. Since the lack of stream flows, even for a short amount of time, would be a major notice of violation, the bypass was installed with automatic backup systems which operated 24/7 for the bulk of the 2 month project duration. Once dewatering occurred, Syblon Reid supported fish rescue operations for the portions of the reservoir that needed to be dewatered.

Two aging slide gates and operating stems had to be accessed via two side-by-side hundred foot long shafts with 4x4 openings near the crown of the dam. Highway 88 goes directly across the top of the dam. In order to access the shaft area and avoid closures of the highway, an old work bench and access road had to be re-established. This access route was on U.S. Forest Service Lands requiring their approval of the work and final restoration measures.

Once the access road was established, the roof of the existing control building had to be removed to allow placement of boson’s chair type swing staging for personnel to perform work at various levels in the shaft and provide a means to lower materials and equipment to the low level outlet tunnel. Once the old gates, stems, stem guides, and operators were removed, 2 new stainless steel gates were put in their place. Cold weather concreting techniques and pressure grouting was necessary on both new gate installations. Syblon Reid also replaced the aging steel outlet trash rack and lake elevation gauging system.

All work was performed without a single first aid injury, OSHA recordable incident, or time loss injury.

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