Brandywine River Restoration Trust removes second dam as part of its restoration project

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In the late 1700s and early 1800s, the Brandywine River powered Delaware’s industrial rise.

Along a 5-mile stretch, more than 130 mills transformed grain, tobacco and other raw materials into flour, cornmeal, snuff and, most famously, gunpowder.

The 12-mile river was dammed 11 times, reshaping its flow to fuel the mills that made Wilmington an economic hub. But centuries later, the dams that once fed progress now stand as barriers to the river’s health. Conversations about removing them began as far back as the 1970s, when scientists and advocates started exploring the restoration of Brandywine’s ecosystem.

It would take decades for the vision to become reality.

In 2019, the city of Wilmington removed Dam 1, a 115-year-old structure near the Brandywine Zoo. It was the first step in reopening the river for fish migration. The latest focus is Dam 6, also known as the DuPont Experimental Station Dam, which was built in 1839 to power the company’s mills. Nearly two centuries later, the Brandywine River Restoration Trust, or BRRT, is dismantling its center section while leaving portions intact on either side. The trust wants to preserve the story of Dam 6 for future generations.

“So we will be putting in signage at the side of the dam that explains the history with a link to our website,” said Jim Shanahan, executive director of BRRT. “And on our website, we will have information describing the dam and its history and its use.”

Pamphlets and guided tours are also in the works, part of the trust’s commitment to honoring the Brandywine’s industrial heritage, even as it works to restore the river.

Dam removal and restoration of ecosystems

Shanahan said conservationists are already noticing the results of removing Dam 1. The portion of the river is now teeming with shads, a species of fish native to the region.

“There was no shad past Dam 1 prior to its removal,” he said. “We actually did studies before removal to confirm that.”

Shanahan said the shads were not able to get past the dam, but once that barrier was removed, the fish returned.

“We worked with the University of Delaware Sea Grant and they were able to identify that American shad, in fact, migrated up and swam past the original Dam 1 and are spawning as we hoped,” he said. “So we sort of call it a proof of life.”

Edward Hale, an assistant professor at the University of Delaware and a fisheries specialist with Delaware Sea Grant, led two surveys on the river to track those changes. His team monitored both juvenile and adult fish populations before and after dam removal.

“Those two surveys we conducted over two or three years … provided a good deal of information in terms of habitat occupancy, but also phenology in terms of trends and when the fish were present,” Hale said. “Juvenile American shad and adult American shad actually really like the habitat just above the site of former Dam 1 and site below Dam 2.”

Though still a hypothesis, Hale said researchers want to keep testing the effects of dam removal on biodiversity.

“So in our same survey, in our net-based survey — not in the adult acoustic tagging — we did note higher levels of biodiversity below the dam. And so we would anticipate that above the dam, if you remove a dam, you potentially would see higher levels of biodiversity,” he said.

The return of shad has spurred a revival up and down the food chain. Shanahan said people have spotted ospreys, which fly over the river and target adult shad for food.

“So on that end of the food spectrum, we’re seeing a change like that,” he said. “But we can presume that it’s also facilitating the population of striped bass, who also feed on shad.”

For the trust, this revival captures the project’s purpose.

“The mission is to return this river to its natural state as much as possible and to allow species, which was what’s extremely popular and quantifiable and a big source of food up and down the Northeast coast, including on the Brandywine, to come back and return to its natural state,” Shanahan said.

From an ecological perspective, Hale added, the impact goes beyond a single species. Dams create habitat fragmentation — cutting off the natural flow of nutrients, energy  and water.

“Each of the dams essentially fragments the entire river corridor and it prevents the movement of energy and nutrients and water between successive fragmented pieces of habitat,” he said.

“Removing all of these dams provides an opportunity to reconnect the ecosystem and then enhance the potential energetic pathways for nutrient delivery into it.”

As the river returns to its free-flowing state, the ecology of the surrounding area will change and similarly bring other environmental benefits like flood reduction, Shanahan said.

What’s next?

Right after the deconstruction of Dam 6, BRRT officials said their next challenge: Dam 2

“It can’t be removed because that dam supplies a race,” he said. “That dam cannot be removed. And there is an alternative method that’s going to be installed to enable the shad to go up past that dam.”

With Dam 6 coming down and Dam 2 on the horizon, Shanahan said Brandywine is entering a new chapter — one where its history is preserved, but its waters run freer than they have in more than 200 years.