Success Story: Black Mountain Streambank Stabilization
Town of Black Mountain addresses streambank erosion with restoration efforts
*Disclaimer: In September 2024, Tropical Storm Helene caused historic rainfall across western North Carolina. Flash flooding and landslides caused devastating damage and loss of life. The storm caused severe flooding, and fast-moving floodwaters carried debris and sediment through the region’s rivers and streams, including the Swannanoa River in Black Mountain. The project described in this case study details the Town of Black Mountain’s efforts to manage streambank erosion and flooding before Helene. The status of this project is not yet known following Helene’s impacts. This case study will be updated with input from the Town of Black Mountain’s project managers as more information about storm impacts becomes available.
Project Purpose
Streambank erosion along the Swannanoa River in Black Mountain, N.C., was threating Veterans Park and the town’s wastewater facilities. Bank erosion and collapse were contributing to significant sediment pollution in the river, clogging waterflow and threatening wildlife. High water speeds in the channel and the frequency and intensity of precipitation caused and were worsened by the stream bank erosion and flash flooding. The Town wanted to find a way to restore the natural environment of the river and water quality while protecting the recreational land and infrastructure on its banks.
Quick Facts
- To address the erosion and flooding issues, the Town of Black Mountain began with the North Fork of the Swannanoa River. The Town had ownership of the land, which made permitting easier. In addition, the North Fork’s location adjacent to athletic fields meant construction was less invasive in this part of the stream.
- The project supported the Town’s goal of improving the water quality of the North Fork so that it could be removed from the list of impaired waters under Section 303(d) of the federal Clean Water Act. The NC Department of Environmental Quality (NC DEQ) identified the Swannanoa River as impaired in 1998 and listed its North Fork in Black Mountain as a 303(d) impaired water in 2006 and 2008. At the time, there were no long-term projects or staff in place to help restore the river and improve water quality.
- The project included bank stabilization, focusing on areas of the river that experienced substantial erosion, utilizing a soft approach of geolifts, riffle zones and existing cobble, creating a more natural bank to deflect the water off the bank. The method is an environmentally friendly way to address the erosion issues in the river, according to the planning director, and will invite habitat for native plants and animals (McCormick, 2021).
- The Town completed the Veterans Park streambank restoration project in August 2021, a few days before Tropical Storm Fred devastated the region.
- Tropical Storm Fred’s record rainfalls — not seen in the region in over 50 years — damaged the restoration project. Despite the significant setback, the Town was determined to repair the project so the stream could be removed from the impaired waters list (Town of Black Mountain, n.d.).
- NC DEQ reevaluates and reports on impaired waters every two years. As of 2022, the Swannanoa River remains on the list, but Town managers are hopeful the river will see significant improvements to its water quality by 2024.
Defining geolifts, riffle zones and impaired waters
Geolifts and riffle zones are bank stabilization tools. As compact soil and vegetation structures, geolifts catch soil and naturally rebuild stream banks. Riffle zones are areas of shallow, fast-moving water.
Impaired waters are stream or river segments and lakes that do not meet certain water quality standards established by the federal government. The term “303(d) list” is shorthand for the list of impaired or threatened waters required under Section 303(d) of the Clean Water Act. Learn more on the Environmental Protection Agency website.
Spotlight on Equity
While this project was not conducted in a disadvantaged community, the restoration of Swannanoa River headwaters is a health benefit to the entire French Broad River system. This type of project could be completed in residential areas to lessen impacts on disadvantaged
| Key Info | |
|---|---|
| Location | Black Mountain, N.C. |
| Estimated Costs | $158,000 |
| Published | March 1, 2024 |
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- In 2018, the Town of Black Mountain used grant funding to pay for engineering projects on the Swannanoa River. The streambank restoration project was designed and shovel-ready when it went to the Town Council for approval.
- The Town Council voted to restore the Veterans Park portion of the streambank along the Swannanoa River in December 2019.
- The Town received additional grant funding in 2019 and 2020 to implement the project from the NC DEQ Division of Water Resources, the Duke Energy Foundation and the Pigeon River Fund. The Town also committed funding to the project.
- Montreat College collaborated with the Town by putting a conservation easement on the land they owned on their side of the river. The easement allows restoration activities.
- Stream restoration began in May 2021, with a focus on stabilizing the eroded banks, lowering the bank slopes and repairing the stream bed using nature-based infrastructure.
- The restoration on the Black Mountain side of the river concluded in August 2021.
Tropical Storm Fred significantly damaged the project within one week of its completion. The structural elements built into the stream survived but some of the bank stabilization measures washed away due to the vegetation not having enough time to take hold. The Town has been working to repair and revegetate the affected streambanks since 2021. They hope to complete the work in 2024. Once the repairs are finished, the Town plans to monitor the project and replant vegetation along the slopes as needed to ensure bank stabilization.
The initial cost of the project was $112,968, covered in part by grants from the NC DEQ Division of Water Resources and the Duke Energy Foundation. To expand the project’s scope, the Town acquired additional funding, with the total cost coming to $158,000. Funding sources included:
- A $74,000 grant from the NC DEQ Division of Water Resources
- $50,000 from the Duke Energy Foundation
- $28,000 from the Pigeon River Fund
- $6,000 from the Town of Black Mountain
Town of Black Mountain; Montreat College
- The Town completed the 2,000-linear foot riverbank restoration project along the Swannanoa River. The project slowed river velocity and decreased erosion using geolifts and riffle zones. Both strategies help stabilize the banks. In addition to slowing the flow of water to reduce erosion, the project’s riffle zones provide habitat for invertebrates (McCormick, 2021).
- The Town opted to straighten a stretch of river with a hard bend. This portion of the river was contributing to significant sediment buildup in the stream. Removing the bend placed the stream in a more natural location and decreased erosion.
- The project removed sediment, large rocks and fallen trees from the river to slow sediment buildup. Workers moved river cobbles to the banks to help prevent further erosion.
- Where the project survived Tropical Storm Fred, the bank stabilization was successful in diminishing erosion (Bick, 2021).
- Project coordinators rescued and relocated five hellbender salamanders upstream of the restoration project (Bick, 2021). The area is not regularly surveyed so the hellbenders were a surprising find.
- Town staff have received feedback that residents now feel safer interacting with the river through fishing and watersport activities.
Black Mountain Planning Director Jessica Trotman recommends having contingency plans for severe weather. “It's not something you can control. Western North Carolina has a particularly narrow window to do these sorts of projects that overlaps with the hurricane season.” High intensity rainfall is becoming more common, so anticipating and planning for the potential impacts of heavy rain on the project will help ensure that ongoing work is not undercut by extreme weather.
Trotman also notes that playing the long game is important. Leveraging public dollars with larger funding sources can help smaller municipalities afford costly projects like this one.
Bick, A. (2021, August 17). Swannanoa River Enhancement at Veterans Park. Retrieved from Headwaters Engineering: https://headwaters-eng.com/2021/08/17/swannanoa-river-enhancement-at-veterans-park/
McCormick, F. (2021, May 14). Swannanoa River Restoration Project Set to Begin. Retrieved from The Valley Echo: https://www.thevalleyecho.com/all-news/swannanoa-river-restoration-project-set-to-begin
Town of Black Mountain. (n.d.). Veterans Park Stream Restoration. Retrieved from Town of Black Mountain: https://www.townofblackmountain.org/2818/Veterans-Park-Stream-Restoration