University hosts forum on effects of dams on rivers

Experts from across the country discussed the effects of dams on rivers.
November 12, 2010

By manipulating the flow of nature itself, large dams provide enough power to light up entire cities, but power comes with a price.

Experts say dams disrupt the flow of the rivers they occupy, which can negatively affect everything in the water.

“Dams are almost always tremendously damaging to ecological systems,” said Pat Nunnally, coordinator for the Institute on the Environment’s River Life program. “The whole way the river works is fundamentally changed.”

River Life hosted a two-day event this week to talk specifically about what kind of damage dams cause, and what can be done to solve the problem.

Gordon Grant, one of the event’s speakers, said that there are two negative consequences of dams that seriously harm ecosystems.

“Virtually all dams block the migration of fish,” said Grant, a research hydrologist with the U.S. department of agriculture’s forest service. There are several strategies that can be employed to help fish continue on their seasonal journeys, but all are very expensive.

Dams also block the flow of sediments that sometimes contain harmful chemicals.

“You may have 40, 50, 60 years of agricultural chemicals that may have come down and accumulated in the sediments,” Grant said.

Historically, dams have also been known to flood large areas of land. Minnesota’s early Native population felt the effects of dams first hand centuries ago when the federal government in the northern portion of the state built dams.

“The impact for Native communities in northern Minnesota was devastating,” said Anton Treuer, professor of Ojibwe language at Bemidji State University, and one of the event’s speakers.

“Wildlife was flooded out, cranberries were flooded out, communities were flooded out,” he said. “The rice crops and the cranberry crops have really never recovered.”

Several strategies to curb the negative effects of dams have emerged since that time. One solution to disrupted fish migration is to build a fish ladder — a lined concrete channel with small steps that fish can navigate over or around the dam. But even fish ladders, which are expensive to build, do not always solve the problem, Grant said.

Another solution is to remove the dams altogether.

“Dam removal has immerged as one of the strategies, but you have to be careful,” Grant said.

Dam removal has become a frequent process in the western half of the Unites States. Usually small dams are removed, where there is not a large amount of sediment stored behind it, Nunnally said.

“It’s tricky. Getting rid of a dam is tricky,” Grant said.  Because dams do not all behave equally on rivers, removing one dam may have a different effect than removing another, he said.

If a dam that has a large amount of sediment stored behind it is removed, the sediment may suddenly rush down the river, causing further harm to ecosystems, Grant said.

Nunnaly said he hopes conversations about dams and their effects will continue in the future and real solutions will be proposed.

“Nothing’s simple,” Grant said. “A dam is not a dam is not a dam … you just can’t paint them all the same color.”

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