A naturally occurring rockslide significantly damaged a 200- to 300-meter-long section of the 5-km penstock that supplies water to the 88-MW Montrose hydroelectric plant.

Needed repairs may require the plant to be off line for several months, says owner Alterra Power Corp. Repairs likely will be carried out during the winter months, when water flows and power generation are lower. The company is currently assessing the cost of repairs.

The intake and power plant were not affected, and there were no injuries. In addition, the nearby 146-MW Toba plant was not affected and remains in operation.

The Toba Montrose project was completed in late 2010 and generates about 710,000 MWh of electricity annually.

Alterra operates six plants totaling 567 MW of capacity.

In June, Alterra and Sliammon First Nation reached an agreement that would allow for the transmission of power from the proposed 1,027-MW Bute Inlet project. The transmission infrastructure for this project is expected to use the existing Toba Montrose corridor.