The complicated physics of removing dams

Dams can fundamentally change large swaths of river ecosystems. But age, disuse and advances in technology have made many dams obsolete. Our environmental news partner, Earthfix, takes a look at the complicated physics behind removing these iconic structures.

TRANSCRIPT

Dams can fundamentally change large swaths of river ecosystems.

But age, disuse, and advances in technology have made many dams obsolete.

We take a look at the complicated physics behind removing these iconic structures.

Our environmental news partner EarthFix has this report.

Grand Coulee Dam, in Washington state, the world's biggest concrete structure.

The mid-20th century was the golden age of dam building in the Pacific Northwest.

Transform a million acres of wasteland into productive farms.

Through these huge...

Salmon runs were still strong then.

And there were few concerns about protecting streams and fish.

Hundred of dams sprung up all over Washington, Oregon, and Idaho.

And now the federal government counts more than 2,200 major dams in the region.

About half of them are pretty small, under 20 feet.

But a 20-foot dam can block salmon from moving upstream just as completely as a 200-foot dam.

Now the dams are getting old, and many have fallen out of use.

There's a growing movement to re-evaluate dams, to figure out whether their purpose for making electricity, controlling floods, recreation, or storing irrigation and drinking water outweigh the challenges they pose for fish.

In some cases, the dams are coming down.

But it's usually not like this.

Most dams don't go in a puff of smoke with a giant stream of chocolate milk coming out the downstream side.

In southern Oregon, two dams, the Wimer and the Fielder, are being removed.

Usually, you very carefully route water around or through the structure.

And then, you slowly and methodically, with a dull butter knife, take the concrete down and gently place it on the side of the bank and into a dump truck.

These two relatively small dams pose big problems for fish.

In fact, they're considered among the worst dams for fish passage in Oregon.

Once removed, though, recovery is expected to happen quickly.

What we've been finding with these dam removals, which has been a big unknown, is that rivers reclaim themselves very quickly, a lot faster than people had realized.

And when they're gone, about 70 miles of salmon and steelhead habitat will open.

In recent years, dams are coming down faster than they're being built.

But this may be a short-term trend.

Dam building goes in cycles.

You know, with climate change and everything, there's a lot more talk about building dams, now or in the future.

But I think we, or at least in the future, we'll have a greater understanding that there are downsides to dam construction.

Dams and salmon don't do well together.

As long as there are people, there will be the need to harness and control water.

And that means most dams are here to stay.