A study of the removal of two dams in Oregon suggests that rivers can return surprisingly fast to a condition close to their natural state, both physically and biologically, and that the biological recovery might outpace the physical recovery.

 

The analysis, published by researchers from Oregon State University in the journal PLOS One, examined portions of two rivers - the Calapooia River and Rogue River. It illustrated how rapidly rivers can recover, both from the long-term impact of the dam and from the short-term impact of releasing stored sediment when the dam is removed.

 

Most dams have decades of accumulated sediment behind them, and a primary concern has been whether the sudden release of all that sediment could cause significant damage to river ecology or infrastructure.

 

However, this study concluded that the continued presence of a dam on the river constituted more of a sustained and significant alteration of river status than did the sediment pulse caused by dam removal.

 

"The processes of ecological and physical recovery of river systems following dam removal are important, because thousands of dams are being removed all over the world," said Desirée Tullos, an associate professor in the OSU Department of Biological and Ecological Engineering.

 

"Dams are a significant element in our nation's aging infrastructure," she said. "In many cases, the dams haven't been adequately maintained and they are literally falling apart. Depending on the benefits provided by the dam, it's often cheaper to remove them than to repair them."

 

 

PHOTO: Removal of Savage Rapids Dam.

CREDIT: University of Oregon.