Underwater lumberjack harvests flooded forests

03/24/04

A CHAINSAW-WIELDING robotic submarine is roving beneath Lois Lake in British Columbia, Canada. But it's not a prop left over from a sci-fi movie. Rather, it's chopping down a forest that was left submerged decades ago when the valley was flooded by a hydroelectric dam. After it cuts the trees, they are floated to the surface, where they are dried out and sold to mills for use in furniture and construction, like any other lumber. Trees left standing in flooded forests die, but they don't rot because the water keeps out oxygen. Worldwide, some 200 million trees are thought to be standing on the floor of hydropower reservoirs. Triton Logging of Vancouver, British Columbia, has been harvesting them for years by sending divers down with chainsaws and then hoisting the waterlogged trunks to the surface (New Scientist, 11 August 2001, p 38). But diving is very slow and dangerous, so Triton has developed a remote-controlled sub to do the job. Called the Sawfish, the 3-tonne, 3.5-metre-long, yellow submersible has high-resolution cameras that an operator on the surface uses to guide it to its target. After grasping the base of the tree in pincer-like arms, it attaches an inflatable flotation bag, which it then fills from its compressed air supply. Finally, it uses its 1.5-metre chainsaw to cut the tree, and lets go of the trunk, allowing the flotation bag to carry it to the surface for retrieval. Triton's president Chris Godsall says Sawfish can cut 36 trees in 3 or 4 hours, operating as far as 300 metres down. Goodsall is planning to make Sawfish submarines for sale to other loggers for CAN$1 million (US$750,000). He estimates that the machines will pay for themselves with three to five years' use - about the same as for other logging equipment.

Source: Eurekalert & others

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