The South's big land puzzle: putting the Roanoke back together again

By Catherine Amos

     The Roanoke River, named by North Carolina Native Americans as the “River of Death” because of its spring floods, is now suffering loss of its ecosystem from the effects of dams upstream.

     In a strategy that is being implemented across the country, The Nature Conservancy is trying to reduce the negative effects of dams on the Lower Roanoke.

     Sam Pearsall, director of science at the North Carolina Chapter of The Nature Conservancy, spearheaded research on the effects of three dams on the river, which flows for 137 miles from southern Virginia into northeastern North Carolina.

     The approach has been applied to other rivers, such as the Savannah and the Altahama rivers in Georgia and the Pee Dee and Congaree rivers in South Carolina.

     “We’ve picked [the Roanoke River] up because of all the ecologically important things there,” Pearsall said. “We selected it for conservation for its own sake. And in order to do that, we had to resolve the flood issue.”

     The Conservancy purchased 10,626 acres from the Georgia-Pacific Corporation in North Carolina to create the Roanoke River National Wildlife Refuge in 1989. In 1994, TNC began managing another 21,000 acres along with Georgia-Pacific, and in 2006, TNC purchased an additional 22,000 acres along the Roanoke from International Paper as part of the largest land conservation project in the southern United States.

     The Nature Conservancy’s main concern is that because the dams regulate the river flow, there is too much water at the wrong time of year in the floodplains of the river, which is causing damage to the ecosystems miles downstream, Pearsall said.

     The conservancy’s goal is a program of “active adaptive management” for the dams on the Roanoke River, so that the dam operators will work in conjunction with the river to help it rather than harm it further.

     The natural floods that claimed human life in the past also gave life to the river environment. The floodwaters, heavy in silt, spread rich soil over the forest floor. Flooded bottomland forests also add vast organic matter to the river, such as decaying leaves.

     The Roanoke River provides habitat for one of the largest and least fragmented bottomland forests in the mid-Atlantic region. The river is also home to more than 200 species of birds, including the bald eagle. When habitats are damaged because of irregular flooding, species are affected as well.

     The three dams on the Roanoke fall across the state line, and include the Kerr Dam (in southern Virginia), owned and operated by the United States Army Corps of Engineers, the Lake Gaston Dam and the Roanoke Rapids Dam, both owned and operated by Dominion North Carolina Power (both in northern North Carolina).

     Kerr Dam, the largest of the three, was finished in 1953 mainly as a flood control project, but for hydropower generation as well. The two smaller reservoirs were built immediately downstream of Kerr for power production. Roanoke Rapids Dam was finished in 1955, 42 miles downstream from Kerr, and Lake Gaston Dam was finished in 1963, built in between Kerr and Roanoke Rapids.

     Jean Richter, a refuge biologist for the Roanoke River National Wildlife Refuge, worked with Dominion, in regulating control of the two lower dams to continue to produce hydropower and control floods, but also allow water releases that mimic natural floods. Richter explained that the Corps regulates the river so that there are no longer any big floods. But, the problem is that there are no “medium floods” either.

     Water naturally flows through Roanoke River anywhere between 57 and 991 cubic meters per second, according to Pearsall. The Kerr Dam, however, maintains a continuous flow at 566 cubic meters per second, which significantly alters the natural flood process.

     “They’ve regulated that river to the point that it’s just a straight line at times,” Richter said. “It’s the same flow, the same flow, the same flow. They’ve taken that variability away in a sense.”

     Downstream, Dominion re-regulates the river yet again. As a result, there are big ecological changes, such as the reduction of certain trees that cannot sustain the steady flows, but both Pearsall and Richter explained that it takes time to track those changes. There is no baseline data that was gathered on the environment downstream prior to the construction of the dams, but there are environmental clues.

     Because of some hundred-year-old trees and the location of old and new plants, Richter said they have an idea of what the floodplain looked like. For instance, oaks were once common.

     Comparing that to the current forest population of sycamores and maples is starting to tell how the dams are impacting them. By observing the new growth of trees on the forest floor and the old trees still there, biologists can start to see how plants fare in different flood situations caused by the dams.

     The oak tree, for example, cannot tolerate being in the water for weeks at a time, and so it dies. Other trees, like the sweet gum, sycamore and the red maple thrive, but when the oaks are dying out, a component of the forest is lost, Richter said. The forest community dictates what kinds of wildlife are present, and changes in the shape of the river have implications for fisheries and aquatic life as well.

     When the general shape of the river changes, Richter said, fish are affected. When the flow of the river changes, often a steep vertical bank forms.

     “There’s a lot of fish and other little critters that can’t really use that steep vertical bank,” Richter said, “whereas if it’s a nicely sloped vegetative bank, it’s more appealing to fish for refuge and for foraging, too.”

     Water quality is also a key component of the health of the ecosystem. Pearsall explained that the way the river is regulated, water gets pushed onto the floodplains at the wrong time of year, where it sits and loses oxygen.

     When the flows are reduced at the dam, the flood water comes back into the river channel very low in oxygen, because when water sits untouched, the level of dissolved oxygen decreases. When the dissolved oxygen in the water is low, the acidity of the water rises, which is deadly for fish.

     “The dams have kind of messed up Mother Nature and how she would be sending flows down the river,” Richter said. “It’s not just for flood control, but for power production. In fact, it seems like power production supersedes flood control a lot of the time. Which is unfortunate, but that’s the reality of it.”

     Phil Townsend, a biologist and an associate professor at the University of Wisconsin, worked with Pearsall in conducting research on the Roanoke River. Townsend explained that he developed a hydrology model that allowed the researchers to look at different scenarios for operating the dams on the river and what areas would be flooded.

     “Because floodplains are floodplains, they have very subtle landscapes,” he said, as opposed to a mountainous area, where the environmental gradients are obvious.

     “You go into a floodplain and a matter of a few inches may be important to the forests and the vegetation,” Townsend said.

     Because of flooding, those few inches can make a big difference in terms of the types of trees that can grow there and how well they perform when they reproduce, he said. With the model he developed, Townsend was able to map the vegetation communities and flood extent to understand how the different types of forests respond to variations in flooding.

     “People think about floodplains and they think, ‘Oh they’re just swamps,’” he said. “But they actually have a lot of diversity. A lot of different types of trees and types of vegetation grow there.”

     To document the extent of the floods, the team on the Roanoke River used a data source called Synthetic Aperture Radar (SAR), which collects imagery of the floodplains from a satellite. Its radar beams can penetrate through forest canopies to measure surface water, rather than simply bouncing off the surface of the vegetation.

     “One way to see if something’s flooded is to put a gauge,” he said, “but you can’t gauge 125 miles of a river with a 5-mile-wide floodplain. You can’t do that. And so, you want to make maps of it, and the SAR is the only way we know of to actually map flooding beneath vegetation canopies.”

     Pearsall and Townsend’s research, “Adaptive Management of Flows in the Lower Roanoke River, North Carolina, USA” was published last year in the journal “Environmental Management.”

     Townsend acknowledged the risk that Pearsall and The Nature Conservancy took to finance the research because it had never been done before, and he is thrilled that their findings are being applied to other areas.

     “That’s the great pleasure for me in this whole process,” he said, “that people are using this to try and make better management decisions for a natural resource.