Corrosion problem could require North Fork Reservoir to be drained

Divers prepare for a dive at North Fork Reservoir to inspect hydraulic equipment. The divers found unexpected corrosion problems that could necessitate draining the reservoir to make repairs (photo courtesy of Jord Gertson).

A problem with the hydraulic gate at North Fork Reservoir could necessitate draining the mountain lake at the headwaters of the North Fork of the South Arkansas River. 

During the Upper Arkansas Water Conservancy District’s October meeting, hydrologist Jord Gertson said he thinks the gate is compromised due to corrosion.

One possible scenario for repairing the damage would require the lake to be drained. The alternative, said Gertson, would be to have divers perform the repairs underwater. “We need more information to decide if we will lower the reservoir and use contractors to do the work or use divers.”

Gertson said all of the water stored in the reservoir would need to be released in order to do the work without hiring divers but that the water could be recaptured in Pueblo Reservoir.

District General Manager Terry Scanga said that, since the district shares the reservoir with Salida, if the reservoir must be drained, “We would talk to Salida about options for their water. They use their water in North Fork for emergency backup.”

Scanga mentioned two possible options: buying the water from Salida or storing Salida’s water somewhere else.

The problem came to light when Gertson accompanied Control Design President Jim Conley to North Fork to install and test a telemetry system that will allow the gate to be operated remotely.

Gertson said that, during testing, the gate would move up but not down, which led to the discovery that the hydraulic system was leaking vegetable oil, which serves as hydraulic fluid because the system is used in an aquatic environment.

Gertson said after the leaks were fixed the problem persisted, which is when he called on the divers to inspect the underwater equipment. He clarified that he was able to close the gate manually, but not using the electric motor to power the hydraulic system.

The divers retrieved a relief valve plug that was heavily corroded and reported to Gertson that all of the stainless steel equipment appeared to be corroded.

The black portion of a stainless steel relief valve plug reveals unexpected corrosion. The plug was retrieved by divers inspecting the Upper Ark District’s hydraulic system that opens and closes the North Fork Reservoir gate (photo courtesy of Jord Gertson).

“We’re thinking the gate is compromised and we’re overworking our hydraulic system to move it.” Gertson said he had requested a quote to replace the gate and parts. “Based on timing, we may be looking at lowering the reservoir to do the work.”

Scanga said the district installed the hydraulic gate and computerized monitoring equipment in 2006. Since the equipment in the water is stainless steel, “It’s troublesome. … In a high mountain reservoir, we shouldn’t be getting this corrosion.”

“We think it could be an electrical grounding issue” causing the corrosion, Gertson said.

Director Rich Hildebrand said he expects that the problem is galvanic corrosion, which can happen when electrical current passes through two different metals that are in contact with one another.

“We don’t know what we need to replace or repair at this point,” Gertson said, but once the old gate is repaired it can be used as a backup. “We’re still waiting for a quote on the equipment. … We’ll try to get all of the parts and get it done as soon as possible; otherwise, we’ll do it in the spring.”

Joe Stone