Loose rock appearing in the water conveyance tunnel at the 1,000-MW Kemano powerhouse was a concern for the owner, who turned to the use of remotely operated vehicles to determine the cause and extent of the problem.
By Robert Clarke
The 1,000-MW Kemano powerhouse is located in a remote area of the Coast Range Mountains in British Columbia, Canada. Water for this high-head generating station is supplied by a 10-mile-long tunnel that was constructed in the 1950s using drill and blast techniques. The hydro plant produces electricity for the owner's aluminum smelter, which is located about 45 miles away.
Small rocks were being found in a trap that had been installed immediately before the turbines. The facility owner was concerned about the origin of the rocks, as the tunnel suffered a collapse in 1961 that required de-watering and repairs. As part of an asset-based condition assessment, the owner decided it was time to inspect the tunnel to determine the likely source of the rocks, review the condition of the previously repaired areas and see the condition of the rock trap, which is in the main tunnel.
|This LBV300XL remotely operated vehicle was used to provide an overall condition assessment of the downstream end of the tunnel providing water to the 1,000-MW Kemano powerhouse.|
Performing the work
Water falls 2,600 feet over the length of the tunnel to reach the power plant, which is 1,400 feet inside the base of Mount Dubose in a blasted cavern. It contains eight turbine-generator units, each with a capacity of 125 MW.
ASI Group of St. Catharines, Ontario, Canada, was selected to provide preliminary inspection services using two of its long-range remotely operated vehicles, or ROVs. These specialized machines provide real-time video and sonar imagery to topside inspection personnel. ASI Group proposed to conduct limited inspections from either end of the tunnel at Kemano to gather a general idea of the tunnel condition and to demonstrate the type of information that could be provided if the full tunnel was inspected using underwater robotic systems.
Because of the remote nature of the tunnel, the two ROV systems were flown in by helicopter from the town of Kitimat, the closest hub for road transportation. From there, secondary helicopter flights were used to deploy the equipment to the surge shaft and intake. The only level area for equipment set-up at the surge shaft was the roof of the structure itself. This provided an area of only 26 feet by 36 feet with limited load capacity for the equipment. Even the helicopter used for personnel transport had to have a mobile landing pad installed adjacent to the structure.
At the upstream intake, there was more room available in the gate house, so ASI Group used its customized Falcon ROV, manufactured by Saab Seaeye and customized by ASI Group, with 3.2 miles of umbilical.
Because power is essential to the aluminum smelter and alternate sources were limited, the tunnel was only available for a four-hour period, during which time all of the lock-out/tag-out operations would have to completed, along with launch, inspection and recovery to the maximum distance possible. The coordinated deployment of the two vehicles began once all systems were locked and tagged, securing the tunnel in a low-flow condition. The extent of the Falcon deployment was about 1.6 miles and covered some of the previous repair areas. Historical records were compared with the observed treatments of the tunnel lining.
At the downstream end, the inspection using the LBV300XL ROV extended about 100 meters upstream to the transition from concrete lining to untreated native rock and downstream to the rock trap.
All of the work was conducted within the four-hour window allotted and to the satisfaction of the plant owner. The coordination between the operations group at the smelter, power management group, site safety personnel and ROV crew culminated in an event that proved not only the capabilities of the ROV, but more importantly, verified the overall process developed by the owner and the team's ability to complete it with a perfect safety record and zero reportable incidents.
|ASI Group workers pilot a remotely operated vehicle during the inspection of the Kemano project's gate house intake tunnel.|
The specifics of the results are confidential to the facility owner, but in general, the work verified that:
- The tunnel could be inspected in a flooded condition using ROVs;
- The type and quality of information was excellent and suitable for an engineering condition assessment;
- The area of previous repairs was in excellent condition; and
- There were some variations between historical records and actual lining treatments.
Bob Clarke, P.Eng., is senior operations manager with ASI Group's marine services group.