After the Breach, Rapid Recovery

By Cynthia Drummond for BRVCA
August 31st 2024

RICHMOND – The dam on the Upper Beaver River breached last December, and the outcome has been decidedly positive for the Beaver River Preserve.

The Nature Conservancy owns and manages the 266-acre property. TNC spokesman Tim Mooney said the breach occurred during a rainstorm, on or around Dec. 23, but pressure on the earthen dam, which was built in the 19th century, had been growing for a while.

“We look back at aerial photos over time, and that flooded area had been growing over a couple of decades,” he said. “You wouldn’t have perceived it on regular visits, but when you step back and look at aerial photos, you can see the pond trending bigger and bigger, and so, it was just a matter of time. Following one of Rhode Island’s wettest years ever, it wasn’t really all that surprising that enough water finally built up to push through the dam.”

Heavy rain may have destroyed the dam, but it was beavers that created the pond. Extirpated from Rhode Island by 1970, they began to return in the ‘80s.

“It’s in the 1980s when that pond starts to reestablish itself, which is roughly the time when beavers started to reappear in Rhode Island,” Mooney said.

Since the breach, the beavers are still around, but they appear to have moved to a smaller tributary.

“The beavers have not rebuilt in or around the manmade earthen dam. That is still flowing freely,” Mooney said. “However, they built a new dam upstream on a little tributary, and so, the southeastern corner of the open area is still flooded. They have built a new dam, close to their lodge.”

Mooney noted that now that the river is flowing freely, the water is remaining cooler, which is good news for native brook trout, a species that avoids water 70 degrees Fahrenheit or warmer.

“It seems like a pretty balanced situation where there’s some open water, which the beavers are maintaining, but the majority of the clearing is allowed to re-vegetate and the water in the Beaver River is not backing up and warming up and raising temperatures downstream for brook trout.”

A fisheries biologist from the Rhode Island Department of Environmental Management is expected to survey the fish population in the coming weeks.

The Plants Return

Botanist Doug McGrady is doing an inventory of the plants that have begun to grow in the newly exposed ground.

“The Nature Conservancy reached out to the Natural History Survey and contracted with the survey to provide a botanist to study the site over the growing season,” Mooney said.

“He has been going out there regularly for the past couple of months, and will continue until the end of September, anyway.”

Seeing which plants begin to establish has been fascinating, Mooney said, even for a seasoned botanist like McGrady.

“Doug described it as a ‘botanical wonderland’ and this is really a key question for the site, but also, for other sites, where public opposition to dam removal is focused on the fear of an unknown aesthetic,” Mooney said.

What is happening at the Upper Beaver River site provides a real - life model for other sites, particularly the Potter Hill Mill dam on the Pawcatuck River, where riverfront homeowners, most of them on the Hopkinton side, have opposed the dam removal because they expect it to result in dropping water levels and exposed mud on the shore.

The Nature Conservancy is one of many groups supporting the removal of the dam, which is the last barrier to migratory fish passage on the river.

“We want to know what happened on our preserve, but also, there are potential benefits to what we can learn at other sites, and so, someone would say ‘you take Dam X out and there’s going to be a mud flat behind it, for how long?’ We couldn’t really answer that question with certainty…and now, we finally have this example,” Mooney said.

Chris Fox, Executive Director of the Wood-Pawcatuck Watershed Association, and a veteran of numerous dam removal projects, supports the Potter Hill Mill dam removal, but he does not believe the Upper Beaver River dam restoration experience will change the minds of Potter Hill Mill dam removal opponents.

“Stinky mud flat is every single dam removal project ever,” he said. “This is not anything unique to Potter Hill.”

On the Upper Beaver River, the site of the former dam began to re-vegetate in May. Mooney said the plants had filled in sooner than anyone had expected.

“We figured we would eventually get to a number that represented some pretty healthy biodiversity. I don’t think we knew that was going to happen by July,” he said. “By June, it was pretty much covered with vegetation, and now, it’s just getting taller and thicker. So far, Doug has identified more than 80 different plants that have come up. Some of them are pioneer plants that would show up after a disturbance, but the majority of plants represent a great diversity of wetland species, so the rushes and the sedges and wildflowers and aquatic plants. You name it: From wild celery growing in the stream to sweet pepperbush growing on the forest edge.”

Fox said he agreed with the TNC’s approach to the dam breach.

“What I am truly enjoying about The Nature Conservancy property is their hands-off approach to ‘let’s just see what happens absent of man manipulation’, when a dam goes and Mother Nature is allowed to perform a succession process, unimpeded,” he said.

Jim Turek, a restoration ecologist who chairs the Richmond Conservation Commission, said he had expected plants, including those germinating from very old seeds, to quickly colonize the site.

“We’ve seen this with many other planned dam removals, anyway, where they take the dam out, and the impoundment is de-watered,” he said. “In some cases, you get sediment movement quite quickly, and even if there isn’t sediment movement in that channel, all that sediment in the basin contains plant seeds, some of which might be more than a century old that are still viable.”

Fox said the dam breach offers a valuable opportunity for habitat restoration research.

“It’s unique for us in the watershed that a catastrophic event like that could occur, that there was no appreciable damage to anyone’s property downstream - which is a testament to why you shouldn’t build around rivers - and the fact that we are given this opportunity to restore this ecosystem back to its natural processes and to study how those changes happen, both in the short and the long term,” he said.

Turek is also looking forward to watching the dam site recover naturally.

“I have always advocated that somebody would do some monitoring of the site, and I sure am glad it’s being monitored by The Nature Conservancy working with the Rhode Island Natural History Survey,” he said. “The channel is going to have a channel adjustment. The channel is creating a new downsize channel that hasn’t been there since the 1880s or so, so you’ve got to understand, you’ve had over a century of impoundment in there by that old, crappy dam and the spillway, and now the  stream is rebuilding and now, hopefully, we get new insect life and native brook trout that are currently in the system that’ll be using that habitat where they haven’t been before.”

Allowing the river to recover naturally, Mooney said, will hopefully enable it to better withstand the extreme weather that accompanies climate change.

“Whatever happens, whatever changes come, the natural system is going to be inherently more resilient to the change, whatever the change is, and so, looking at places to remove dams and restore free-flowing streams is giving these ecosystems their best shot at surviving climate change,” he said.