Swannanoa River Restoration Project: Flooding causes setback
Although the Swannanoa River restoration project was near completion, nearly all the work has to be redone thanks to the recent flooding, according to Josh Harrold, Black Mountain town manager.
"I think a lot of that's due to it being so new and not having time to establish," Harrold said. "We're going to have to do some work out there to fix that."
Tropical Depression Fred brought the most rainfall to Buncombe County in more than 50 years, according to Jeff Robel from the National Centers for Environmental Information.
From Aug. 16-17, the county received 5.33 inches of rain — a two-day total surpassed only twice before on Oct. 4-5, 1964 when the area received 5.59 inches of rain and Aug. 21-22, 1967 with 5.44 inches of rain, Robel said.
As a result, the project, aimed at stabilizing a linear 1,700 foot section of the river at Veteran's Park, suffered a major setback as the river flooded its banks.
Having suffered bank erosion, degraded aquatic habitats, fine sediment pollution and loss of land, the project partnered the town of Black Mountain with Headwaters Engineering, the work being performed by Baker Grading & Landscaping.
"We added some grade control structures to the stream, did some flood plane grading to allow the water to get up and out of the streams to hopefully prevent future erosion," said Aaron Peacock of Baker Grading & Landscaping.
In addition to providing embankment repairs, Peacock said he was able to help relocate endangered species, rescuing five hellbender salamanders throughout the project.
Harrold said the restoration project was a continuation of the Upper Swannanoa River Watershed Management Plan from a few years ago. This initial plan contained a list of action items to improve the impaired waters and embankments.
According to Harrold, a long-term goal of the larger plan is to remove the section of the Swannanoa River from the EPA's 303(d) list, a catalog of impaired or threatened waters. Since the plan also addresses issues in the areas surrounding the river, the cleanup project has helped remedy much of the sediment loading, as well as runoff into the river.
"We're trying to set the stage for the river to adjust naturally over time with these earth work measures," said Andrew Bick, principal engineer for Headwaters Engineering.
In one section, where the river had become widened due to erosion, the sediment runoff had deteriorated so much of the bank that the earth work had to correct the dimensions of the river itself, according to Bick.
Through the use of bioengineering, only natural materials were used for this project, allowing for a longer-lasting effect once trees and shrubs are planted on the banks this coming winter. The root masses of the new plants, coupled with the natural materials, should hold more firmly and prevent erosion.
"In terms of stability, it's kind of like rebar and concrete," Bick said. "The root masses of those trees and shrubs help hold the soil in place."
Whereas in previous years the engineers may have utilized large rocks to armor the bank, this actually tends to transfer the issue downriver rather than provide a solution. The minimal stability of armoring also doesn't provide necessary resources for the habitat that trees and shrubs would provide in the form of shade over the river.
Bick said that repairs are planned and additional action will be necessary since the area experienced excessive flooding. As this was not a comprehensive restoration, meaning the work was focused on only the severely problematic areas, Bick said the area will continue to be monitored for the next several months with the contractors taking action when needed.
Looking ahead, the town plans to update the best management practices of stormwater so as to help clean the water before it ends up in the river. Harrold said measures such as this will be taken all around town in an effort to trap storm runoff before it enters the Swannanoa River.
The project finished nearly three weeks ahead of schedule, according to Bick. Due to the flooding, the engineers will assess the damage and return to the worksite to conduct repairs. Once repairs have been completed, new life can be planted along the banks of the river to cement the work in place.
"This has been a really good project, and we'll build on this success as we move forward," Harrold said.