Marmot Dam explodes into souvenir bits
It was one small step in the removal of a dam, but to environmentalists, it was monumental.
The top of Marmot Dam exploded Tuesday morning in a cloud of white dust and yellow gas as a crowd of river and fish advocates cheered and snapped pictures.
“It feels really good to be holding a chunk of the Marmot Dam in my hands,” said Amy Souers Kober of American Rivers.
The Sandy River isn’t yet flowing free. It will take several weeks for PGE contractors to remove the dam and several months for winter storms to wash out a temporary construction dam upstream.
But more than 200 people celebrated the beginning of the end of Marmot – the largest dam ever removed in Oregon.
About 2,400 pounds of ammonium nitrate fuel oil and 1,900 pounds of high-velocity gelatin dynamite softened the top 10 feed to the 47 foot structure; the explosion pushed the rear of the dam back 12 feet, contractor Jerry Dilley of Superior Blasting said. The blast was planned so precisely that only a few small particles flew onto a nearby riverbank, where some spectators later scooped them up as souvenirs.
For many, “to have a climactic moment, even though it’s just another step (in the removal), is very exciting,” said Sue Doroff of the Western Rivers Conservancy. The group is helping assemble a 9,000 acre recreational area in the basin with a 1,500 acre donation from PGE.
PGE decided about 10 years ago not to relicense the hydroelectric project that includes Marmot. Although the project generates enough power for about 12,000 homes, rules to protect migratory fish were becoming more strict and meeting them would be costly. Analysis at the time showed those costs exceed the value of the project’s power, PGE CEO Peggy Fowler told the crowd.
The decision was “absolutely a close call,” Fowler said after the blast, and would still be today, especially given the rising value of power.
However, removing the dam remains “the right decision” she said. “It’s a small amount of energy, and that makes it easier.”
The company that built the current concrete version of Marmot in 1989 was chosen to remove it this year.
Emotionally, “it’s a little tough” to pull apart a dam that was meant to last for a century, said Natt McDougall of Natt McDougall Co. of Portland.
PGE will remove most of the rest of the project – including a smaller dam on the Little Sandy River and manmade Roslyn Lake – next year.
Workers are taking several steps to keep the demolition from harming fish.
Last week, the Oregon Department of Fish & Wildlife held a “salmon rodeo,” said Todd Alsbury, the agency’s district fisheries biologist. Workers waded in to net more than 400 spring chinook that had gotten trapped between marmot and a temporary fish trap installed downstream.
The fish weighed between 10 and 30 pounds each.
“There were a few bruises,” to the fish wranglers, he said.
The agency is also planning a rescue program for fall chinook. Experts are worried that the 1.2 million tons of sediment trapped behind the dam could smother spawning beds and eggs when it washes down. Just in case, the agency will capture 10-20 pairs and rear their eggs in the hatchery for a short time.
Although some fish advocates want the agency to capture more pairs and preserve a larger gene pool, Alsbury said that would be costly and would risk removing too many fish from the wild run.
For most of the fall, PGE and other agencies working on the removal will be “in a holding pattern,” said Dave Heintzman, project manager for PGE. When forecasters predict high river flows, workers will push dirt into the channel diverting water from the temporary construction dam. They will turn on de-watering pumps, allowing that dam to become saturated with water.
Scientists studying the project are eager to see what will happen to the river and its fish.
“It will be nerve-racking for us to go through this winter to see how the sediment moves down,” Alsbury said. “But at the same time, it will be exciting.”