Granite Geek: Flooding means we need fewer dams, not more (much to my surprise)


Granite Geek

Published: 07-20-2023 10:18 AM

For years I have written enthusiastically about programs to remove the thousands of outdated dams in New England, freeing up rivers to let fish swim free and ecosystems recover.

But then came the recent floods and the promise (or should I say threat?) of much more to come and I had second thoughts.

As the atmosphere gets warmer it can hold more water, which occasionally gets released in relentless downpours that overwhelm systems created to contain a world that no longer exists. Our daily life is going to be seeing a lot more “historic” floods. So maybe, I thought, we should stop removing dams.

That makes sense, right? There’s a reason we built dams like Hopkinton-Everett and a dozen earthen dams in the hills around the Monadnock region: To hold back water as needed and slow down onrushing torrents.

New Hampshire has a lot of dams – 4,800 or so according to the state, most of them very small – and my thinking would be correct, said Amy Singler of American Rivers, except for one thing: “The majority of our dams do not provide flood control.”

Most of the dams in New Hampshire were built to provide local power, often to a mill. They are “run of river” dams and aren’t very tall, holding back water enough to be channeled to a water wheel, turbine or other power system without creating much of a deep pool upstream. And except for serious drought, those pools are always full as water trickles or pours over the spillway.

“The impoundments are more or less full,” said Singler. When a flash flood descends from on high the water just barrels right over the dam. “They’re not really providing any additional flood attenuation, flood storage.”

What they are doing is blocking fish passage, turning rivers and streams into a long series of disconnected bits. Removing dams can be startlingly effective at fixing the problem, with the poster child being the removal of dams on the Kennebec River in Maine that has produced a near-record haul of alewife. That’s an extreme case but it shows how much damage dams can do to a river system.

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That’s why American Rivers, a national non-profit, is working to remove unnecessary dams: 65 of them in 2022 alone. Singler is a director of river restoration for the organization.

New Hampshire also has a dam-removal and river-restoration program under the Department of Environmental Services that in recent years has removed the Tannery Brook Dam in Boscawen, Berry Brook Dam in Pittsfield and two Buck Street dams on the Soucoock River in Allenstown and Pembroke, among 35 projects statewide. Six more removals are planned for the next two years.

Environmental issues aren’t usually the main reason a dam comes down, however. The real impetus is that they can be dangerous.

“There’s a saying that the best day that a dam has is the day it is built,” said Singler. “Whether it’s water, time, wind, sun, they are slowly degrading from day one.”

Without maintenance, which can cost big money, they can fail.

I once covered a case in southern New Hampshire where a dam in the woods, so old and small that most people who had built homes in the area didn’t know it existed, gave way suddenly. Even though it was on an ordinary woodland creek and it was an ordinary flood-free summer, the resulting cascade blasted into a house and did a lot of damage. Nobody was hurt but the lawsuits started flying.

One of the things that state officials are doing right now is checking on dams, to see whether the flooding might have damaged them.

“Small dams have essentially been inundated. We won’t see if there’s damage or if those dams have failed until the flood waters start to recede,” said Singler. “They’re not providing any benefit … and they add to the uncertainty. Anything we can do to limit uncertainty during flood events is going to make our communities safer.”

“Whenever we can remove dams that are not needed, that are aging, that’s going to make for safe communities in addition to benefits about habitat, fisheries, and cleaner and healthier water.”