However, by 2019, significant cracks and deterioration in the dam’s upstream face prompted concerns about its stability, particularly when the Montana Department of Natural Resources and Conservation (DNRC) warned that failure to address the issues could lead to reservoir-level restrictions. In response, BSB commissioned Great West Engineering to draft a Preliminary Engineering Report (PER) in 2021, assessing the dam’s condition and proposing several repair alternatives. The proposed solution involved removing and replacing the existing parapet wall, partial removal of the concrete cap, and installing post-tensioned anchors to improve stability. With the design finalized in 2023, a contractor was selected and the construction began in April 2024.

The rehabilitation process kicked off with the removal of 300 cubic yards of deteriorated concrete using a concrete wire saw, a specialized tool that cuts through concrete with a diamond-embedded wire. The wire is continuously rotated around the material and is then slowly pulled through, allowing for precise controlled cuts.  Due to limited access, barges were used not only to transport the concrete debris but also to serve as floating work platforms. Once the old concrete was cleared, the team started to pour the new dam face. A large, 61-meter concrete pump truck was needed to overcome the 80-foot elevation difference and 150-foot reach from the base of the dam to the crest. The new concrete was specially mixed to resist water, freeze-thaw impacts, and shrinkage while welded PVC waterstops were incorporated into the joints to prevent water seepage and future deterioration ensuring the dam’s longevity for years to come.

The installation of post-tensioned anchors at Basin Creek Dam required the expertise of a specialized contractor. A post-tensioned anchor consists of a steel bar embedded through a structure, anchored at its base, and then tensioned to enhance its stability. This technique helps resist forces such as sliding, overturning, and bending that the dam may encounter over its lifetime. A total of 12 anchors were to be installed along the crest of the dam to ensure its continued safety and resilience.

To install the anchors, drilling equipment was used to bore through the existing concrete and granite blocks, reaching deep into the dam’s core. Given the remote location, barges were once again employed to transport a track-mounted drill rig across the reservoir. Once lifted onto the dam’s crest, the rig would begin drilling the holes necessary to install the anchors. After the holes were drilled a series of grouting, redrilling, and watertightness testing was completed on each hole to obtain a sealed anchor hole. As the holes were drilled, the contractor discovered significant voids between the original, hand-stacked granite blocks. These gaps allowed water from the reservoir to seep into the anchor holes, complicating the sealing process. Multiple iterations of grouting, redrilling, and watertightness testing were required before the holes were adequately sealed.

Eventually, the anchor holes were ready, and the installation of the steel anchor bars could begin. Designed with Class I corrosion protection, the bars were encased in corrugated HDPE sheaths and filled with grout to increase their longevity and durability. However, due to the rough terrain and difficult access, the bars and corrosion protection were at risk of being damaged during transport, potentially compromising their corrosion resistance. To mitigate this risk, the contractor adopted an innovative solution to minimize handling: helicopter installation.

The morning of the anchor bar installation was filled with anticipation to watch the helicopter work. A large group of stakeholders gathered on-site as a helicopter arrived from Bozeman at 8:00 a.m., landing at the park a quarter mile from the dam. The pilot, alongside the contractor, conducted a safety briefing and a walk-through of the site, safety plan and hand signals for communication. At 8:50, the first anchor bar was lifted into place, and from that point, the process moved swiftly and smoothly. Within just 40 minutes, all 12 bars had been installed, with the helicopter returning to Bozeman after refueling. The entire operation, impressively, took under two hours to complete.

Helicopter Post-Tensioned anchor Pickup and Dam Install