oregonpackfan
07-30-2008, 09:26 PM
Months ago, a dam was removed from the Sandy River in Oregon. Despite the use of fish ladders, dams have been a major impediment in salmon migration and spawning.
When a dam had to be removed recently, scientists feared the buildup of sediment would ruin salmon sites downstream. It had little effect on the downstream spawning sites. The dam removal also opened up spawning sites upstream.
Freak Out, do you have these controversies about salmon and dams up in Alaska?
Oregon's Sandy River successfully reinvents itself after dam removal
Scientists are impressed how fast the river is digesting Marmot Dam sediment
Wednesday, July 30, 2008
MICHAEL MILSTEIN
The Oregonian Staff
SANDY -- As dams go, Marmot Dam on the Sandy River wasn't huge. But now that it's gone, its impact is turning out to be enormous.
The removal of the nearly 50-foot-high dam by Portland General Electric in October gave scientists perhaps their best chance to watch as a river digested a vast amount of rocks, sand and gravel collected over many decades in a reservoir.
Some had worried that sediment piled behind the dam would suffocate salmon and block tributaries downstream. It did nothing of the sort. In fact, the river has since digested the equivalent of about 150 Olympic-size swimming pools full of sediment -- without a hiccup.
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"Never has this much sediment been released at once into such an active and hungry river," said Gordon Grant, a research hydrologist with the U.S. Forest Service's Pacific Northwest Research Station. He has studied the dam removal and given presentations on the results at conferences from Sacramento to Venice, Italy.
He was just invited to give his Marmot Dam talk in China.
"There's a global interest right now in river restoration," Grant said. "Marmot is certainly one of the best-documented and most spectacular examples of dam removal in the sense that the river was allowed to process the material itself."
The river has so far removed about half the material backed up behind the dam. It's difficult to tell that a dam once blocked the popular salmon stream. The river shoves and piles gravel and cuts into the shore the way a healthy river should.
Scientists were especially impressed with how rapidly the river scoured the sediment away. Some models predicted the river would need two to five years to carry off half the sediment pile, but it did so in months.
Though some officials had worried that the sediment would linger and pose an obstacle to fish, federally protected coho salmon were swimming upriver the day after the dam crumbled. Salmon spawned in the river as they always have.
"This was a grand experiment that came out just like people hoped it would," said John Esler, project manager in PGE's hydropower licensing division.
CONTINUED 1 | 2 | 3 Next
When a dam had to be removed recently, scientists feared the buildup of sediment would ruin salmon sites downstream. It had little effect on the downstream spawning sites. The dam removal also opened up spawning sites upstream.
Freak Out, do you have these controversies about salmon and dams up in Alaska?
Oregon's Sandy River successfully reinvents itself after dam removal
Scientists are impressed how fast the river is digesting Marmot Dam sediment
Wednesday, July 30, 2008
MICHAEL MILSTEIN
The Oregonian Staff
SANDY -- As dams go, Marmot Dam on the Sandy River wasn't huge. But now that it's gone, its impact is turning out to be enormous.
The removal of the nearly 50-foot-high dam by Portland General Electric in October gave scientists perhaps their best chance to watch as a river digested a vast amount of rocks, sand and gravel collected over many decades in a reservoir.
Some had worried that sediment piled behind the dam would suffocate salmon and block tributaries downstream. It did nothing of the sort. In fact, the river has since digested the equivalent of about 150 Olympic-size swimming pools full of sediment -- without a hiccup.
Advertisement
"Never has this much sediment been released at once into such an active and hungry river," said Gordon Grant, a research hydrologist with the U.S. Forest Service's Pacific Northwest Research Station. He has studied the dam removal and given presentations on the results at conferences from Sacramento to Venice, Italy.
He was just invited to give his Marmot Dam talk in China.
"There's a global interest right now in river restoration," Grant said. "Marmot is certainly one of the best-documented and most spectacular examples of dam removal in the sense that the river was allowed to process the material itself."
The river has so far removed about half the material backed up behind the dam. It's difficult to tell that a dam once blocked the popular salmon stream. The river shoves and piles gravel and cuts into the shore the way a healthy river should.
Scientists were especially impressed with how rapidly the river scoured the sediment away. Some models predicted the river would need two to five years to carry off half the sediment pile, but it did so in months.
Though some officials had worried that the sediment would linger and pose an obstacle to fish, federally protected coho salmon were swimming upriver the day after the dam crumbled. Salmon spawned in the river as they always have.
"This was a grand experiment that came out just like people hoped it would," said John Esler, project manager in PGE's hydropower licensing division.
CONTINUED 1 | 2 | 3 Next