Work crews have been fighting the elements since November in the middle of the Brandywine River. Heavy rains over the past six months have caused some problems for workers demolishing a 115-year-old dam near the Washington Street Bridge in Wilmington.
The three-foot high dam was built to allow city water pipes to cross the river. Those cast iron water mains will be replaced by flexible iron pipes that will be buried beneath the river bed.
Heavy rain last week pushed the river higher, flooding the work site. “We got flows that were about eight times the flows that you normally would have this time of year, and it created a breach of our temporary dam and it flooded out the excavation area,” said Sean Duff, the city’s water division director.
And though the project was necessary for the city’s water infrastructure, the change will have environmental benefits too. “Take that project and enhance it by restoring the river to its natural flow and the natural bed that is under there,” said Martha Narvaez, policy scientist at the University of Delaware’s Water Resources Center. “The idea is that when they remove the dam, or the concrete encasing from the piping, that the fish that weren’t able to migrate further up river will now be able to migrate further upriver.”
For centuries, American shad fish would leave the salt water in the ocean and travel upstream in freshwater rivers to spawn. But because shad aren’t able to leap out of the water like salmon can, the species has been unable to travel very far in the Brandywine or the nearby Christina River.
But even with this dam being removed, fish will only make it about a half mile further upriver before they encounter the City Dam. “That dam is going to be more challenging in terms of we can’t remove the dam because it’s really our water source,” Duffy said. “Maybe they can build something that will allow fish passage upstream like fish ladders or fish ramps or fish elevators.”
About two dozen people toured the project last week to learn more about the effort as part of a partnership between the state section of the American Water Resource Association and the group Clean Water: Delaware’s Clear Choice. “What I love most about it is it’s interested citizens, it’s professionals, it’s academics, it’s all sorts,” Narvaez said. “Everyone was coming from a different perspective.”
Narvaez is part of a group at UD that was awarded federal grant money last week to fund more research into other dams in the state that prohibit the movement of shad.
“We’re going to be looking at the dams upstream and looking at what their function is, what their purpose is and sort of the physical characteristics of it, and then to see if we are able to remove those,” she said. “Ideally, you remove them. There’s some that you may not be able to remove for historic purposes or actual purposes that they’re serving in the river such as the drinking water intake in Wilmington.” — (WHYY)