Upper Ark District completes underwater repairs at North Fork Reservoir

Scuba divers prepare to repair water-release infrastructure at North Fork Reservoir. The water-release equipment is vital to the Upper Arkansas Water Conservancy District's ability to efficiently operate the reservoir, which stores augmentation water for Salida as well as the District (photos courtesy of Upper Arkansas Water Conservancy District).

Divers contracted by the Upper Arkansas Water Conservancy District recently completed repairs on the water-release infrastructure at North Fork Reservoir during 3½ days of diving in the frigid mountain reservoir.

Hydrologist Jord Gertson reported on the work during the District’s September board meeting in Salida. He explained that, due to the high elevation, each of the three divers was limited to 70-minute dives.

Repairs involved replacing the water-release gate and other corroded parts, tightening hydraulic fittings, flushing the hydraulic lines and replacing the hydraulic fluid.

Gertson first became aware of a problem with the dam infrastructure while installing equipment to allow remote operation of the release gate. He discovered that the hydraulic system was leaking vegetable oil, which serves as hydraulic fluid because of the aquatic environment.

Gertson called in divers to inspect the equipment in the reservoir, and they documented excessive corrosion of stainless-steel components, attributed to cathodic corrosion, which can happen when dissimilar metals contact one another in the presence of electrical current.

Effecting repairs revealed additional problems. “The original problem appeared to be hydraulic integrity,” Gertson said. “A relief valve failed and probably pulled water into the system. … When water mixes with vegetable oil, it can cause clogs.”

Gertson attributed loose hydraulic fittings to repeated pressurization and depressurization over the years since the hydraulic system was installed. “Sludge in the lines was part of problem,” given the increased pressurization required to operate the system due to the sludge caused by water in the lines.

Gertson reported, “We now have a fully functioning gate with new electronics.”

Replacing the gate without having to drain the reservoir hinged on the integrity of the pipeline and valve below the release gate.

Gertson said District Engineer Chris Manera tested the lower valve before the divers arrived, and no issues were observed during the repair work; otherwise, they would have needed to drain the reservoir to perform the repairs.

With repairs accomplished, Gertson said the remote operations project should be complete by October.

Joe Stone