By Sandra Villasenor
While walking alongside a stream on your property or nearby park, have you noticed any rapid stream bank changes, especially after rain events? For instance, the stream channel widening, steeper slopes and missing chunks of the stream bank. Have you ever wondered what defines a healthy stream bank or river bank?
Around 100,000 people migrate to North Carolina every year. In response, more homes, apartment complexes, parking lots, and streets are constructed. The increase of impervious surfaces prevents rainwater from soaking into the ground and instead it becomes runoff, eventually flowing directly into waterways at a higher volume and velocity. Just 1” of rain falling on a one-acre parking lot can generate over 27,000 gallons of runoff into our urban streams! All of this stormwater runoff can cause streambanks to erode at a faster rate, especially streams that do not have a healthy riparian buffer.
What is a Riparian Buffer?
A riparian buffer is a vegetated area alongside streams, rivers, wetlands and lakes. A healthy riparian buffer contains a diversity of native trees, shrubs, grasses and flowering plants. Riparian buffers provide many benefits for human and ecological communities: improving water quality, streambank revitalization, regulating temperature, flood control, habitat for wildlife and aesthetic value. They act like a “sponge,” soaking in precipitation and filtering stormwater runoff. The riparian plants also help stabilize the streambank, with the roots holding the soil in place and reducing streambank erosion.
What does a Healthy Stream Look Like?
The 2020 Water Quality Assessment by the NC Department of Environmental Quality revealed that 70 percent of NC streams are impaired and need at least some form of streambank repair. Almost all urban streams need either streambank repair or reconstruction (requires engineering and permitting).
An example of a stream with a poor riparian buffer is Nasty Branch (Town Branch), located in the River Arts District. In some sections of the stream, the slope of the bank is steeper and shows land loss (missing chunks of land). A steep bank with no native vegetation will continue to erode and lose land. A mix of native trees, shrubs and tall grasses with deeper roots will help hold the soil to the banks. Just using turf grass is not helpful in stabilizing as the roots only grow a few inches into the soil. In other places, where willow and birch trees grow, the streambank is healthier.
Characteristics of a healthy stream, such as Buttermilk Creek in West Asheville, are stable banks with a gentler slope, native plant vegetation and a mix of pools and riffles. Pools are deep areas with slow water where fish and other aquatic animals like to hang out. Riffles are shallow areas with fast-running water that splashes over rocks.
Sandra Villasenor is currently an AmeriCorps Project Conserve member serving as the Watershed Coordinator at RiverLink, an environmental nonprofit with the mission of promoting the environmental and economic vitality of the French Broad River and its watershed. To learn more, visit RiverLink.org.
Tips & Practices to Help Protect Our Streams
• Refrain from mowing or cutting down vegetation. Give at least 15 feet of space between stream and mowed edge.
• Plant native streambank plants that are naturally adapted to grow near streams. Ask for native plants that are available from local growers and nurseries, and avoid invasive species. Emphasize that you want native species for landscaping and conservation purposes.
• Tall trees such as river birch (Betula nigra), yellow buckeye (Aesculus flava) and sycamore (Platanus occidentalis) are good for streambank stabilization.
• Smaller trees are also a good option. Some small tree species that stabilize quickly are box elder (Acer negundo), serviceberry (Amelanchier arborea) and spicebush (Lindera benzoin).
• When planting closer to the stream, consider planting shrubs that do well in wetter conditions, like sweetshrub (Calycanthus floridus) and buttonbush (Cephalanthus occidentalis).
• Placing livestakes, installed into the bank during the winter months (November to February), is also a good and cost-effective method. Livestakes are dormant cuttings from native trees and shrubs that will sprout during the spring.
• Consider planting during the fall to allow time for the roots to grow before the summer months.
Riparian buffers and native plants are important elements in helping to protect our waterways. For other resources on native riparian plants and streambank repair methods, visit the NC Cooperative Extention at content.ces.ncsu.edu and henderson.ces.ncsu.edu, and use the search bar to find specific information.