Western North Carolina dam removal clears the way for imperiled species
As a handful of people watched, heavy machinery obliterated the powerhouse for North Carolina’s Dillsboro Dam, the most visible sign yet of the impending removal of the 12-foot high dam itself, scheduled to begin in early February.
Dillsboro Dam, built in 1913, is one of a series of Duke Energy hydropower facilities on western North Carolina’s Tuckasegee River. Federal law requires operators of private hydropower dams to address impacts to fish and wildlife. Duke Energy’s decision to remove dam is seen as a major part of that effort on the Tuckasegee River and will aid the recovery of a pair of imperiled species – the federally endangered Appalachian elktoe mussel and the sicklefin redhorse fish.
“It’s not very often you get to see a dam demolished, especially a FERC-licensed hydroelectric project. But this is in the best interest of the American people” said Mark Cantrell, the U.S. Fish & Wildlife Service biologist involved with the project. “We have a rare opportunity to see the return of a stretch of river that’s been impaired for nearly 100 years. This means a lot for the fish and wildlife in that river, especially the rare Appalachian elktoe and the sicklefin redhorse.”
Dillsboro Dam prevents most fish, crayfish, and other stream animals from moving up- and downstream, splitting some aquatic wildlife populations while preventing others from accessing otherwise quality habitat. The Appalachian elktoe mussel is found both above and below the dam, and removal will help reconnect the bisected population. Fish surveys have documented greater diversity below the dam than above, including 10 species not found above the dam at all. Dam removal will provide access to upstream habitat not only to these fish, but also the sicklefin redhorse. This migratory fish is found in the lower reaches of the Tuckasegee River and is the focus of efforts to boost its numbers, including creating a population that will swim further up the river, into habitat made available by dam removal.
For the past century, nearly a mile of the river has sat impounded behind Dillsboro Dam. In this reach, sediment has settled on the stream bottom, covering the natural sand and rock bottom that supports native life. Water at the bottom of the reservoir is also lower in oxygen and colder than free-flowing river water. The biological impact of the reservoir can be seen in the fact the Appalachian elktoe is found above and below, but not in the reservoir, and biologists found 11 species of fish in the reservoir, while the river immediately below the dam had 38 species and the river stretch above had 24. Restoring the reservoir to a free-flowing river will make this reach usable to a suite of native fish and other aquatic animals.
To protect the endangered elktoe mussel during demolition, teams of biologists collected mussels from the area immediately below the dam and moved them upstream out of harm’s way. In total, 1137 elktoes were collected. There were 54 specimens of wavy-rayed lampmussel also collected and moved. After the dam is removed and the river becomes stable, the mussels will be returned.
Another short-term concern has been addressing the 100,000 cubic yards of sediment estimated to rest behind the dam. The Service tested the sediment, finding no contaminants of concern. 63,000 cubic yards of sediment were dredged and deposited at an upland site, with more to be removed during demolition. Most of the sediment not dredged will be stabilized in place on the newly exposed riverbanks, secured by landscaping using native plants. Some minor amounts sediment will be gradually released during demolition, eventually settling into the next reservoir downstream, one of the largest in North Carolina, where it will not have a noticeable impact.
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