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When Flooding Is Good
Northeast Environmental Hub
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Walking the Fine Line Between a Natural River and Controlling Floods


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4:10 minutes (4.01 MB)
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The more than 70 large dams on the Connecticut River control the flow of water to accomplish different goals, such as generating electricity and mitigating the impact of floods.  But a new study on the river is investigating whether water could flow more naturally without hampering these dams. As part of a collaboration with northeast stations Nancy Cohen from WNPR in Hartford reports on an effort to restore threatened floodplains, an ecosystem that can soften the blow of floods.

Inside the Union Village Dam gatehouse in Thetford, Vermont Hydraulic engineer Greg Hanlon of the U.S. Army Corps of Engineers points to two hulks of metal.

“These two here, they operate 8 foot by 12 foot steel gates that  can close off or open the conduit to varying degrees. “

On this fall day the flood gates are open. The water that flows in from a tributary of the Connecticut River flows out. Just like an undammed river. But when there’s a threat of flooding the gates are lowered.

“During the spring when we have downstream concerns or high rain events we would operate these fairly frequently.”

The Connecticut River has had its share of floods. After the devastating flood of 1936 the federal government decided to put flood control dams on the river. But besides dams, floodplains form a natural buffer against floods.

On a wide floodplain in East Hartford, Connecticut forest ecologist Christian Marx of the Nature Conservancy is pulling a measuring tape around a stout silver maple.

“So this a nice one. This is 612 centimeters circumference. That could be the biggest one we’ve found yet.”

This tree is more than twenty feet around. As part of a study conducted by the Nature Conservancy and the U.S. Army Corps of Engineers Marx is trying to find out where the healthy floodplains are on the Connecticut River and how much water they need. He says when the river floods it carries sediment and nutrients which feed the lush floodplain forests.

“All the resources that a tree needs to grow are really abundant here.  And so you get these really luxurious forests, kind of like a tropical rainforest, big trees, the herbs in the understory can be as tall as a man.”

Marx isn’t exaggerating. I walked through six foot, seven foot high nettles, which in my experience usually grow much smaller. And there was poison ivy, vines and all kinds of stuff.

This kind of no-mans land is good for wildlife. Wood ducks and mergansers nest in tree cavities. Muskrats burrow on the river’s edge.

Standing upstream on a bridge over the river in Massachusetts Kim Lutz of the Nature Conservancy says floodplains also benefit humans.

“They are the first buffer when a flood is coming down the river that provides that water storage. It slows down the river and protects human development along river systems.”

Many of the floodplains were lost long ago when the major cities on the Connecticut River were built and farm fields were ploughed. Roughly half of the floodplain acreage in the river basin has been lost to development and farms fields, said Lutz.

“Also there are forests that have changed because the flow has changed whereas there might be a forest that’s high and dry it used to be a wet forest due to dam management. “

Researchers from the Nature Conservancy and the Army Corps are building a computer model that simulates how all the dams on the river operate now. And whether it’s possible to provide more environmental benefits without infringing on human uses like hydro power, recreation and flood control.

The Corps has already altered the flow of water to benefit the environment, said Greg Hanlon, a hydraulic engineer with the Army Corps.

“There’s a fine line between flooding a field and flooding a house next to the field.”

It is a very tight balancing act, said Hanlon.

“We may be getting to the point that we’ve done all that we can do without sacrificing our main mission of flood control. Maybe not. And maybe these models will help us push the grey areas a little more to the environmental side or maybe not, Hanlon said *

Ultimately Hanlon says it’s the corps that has to answer to the public in the wake of a flood. But the Nature Conservancy says the ecosystems also deserve an answer.

Northeast environmental coverage is part of NPR’s local news initiative

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