*This is the third post in a continuing series on backyard stream management.*
Eroding streambanks are one of the most common landowner technical assistance calls that we receive at Cuyahoga SWCD. Often, homeowners cite the charm of the “little creek out back” as something that attracted them to the property. We hear stories of kids catching frogs in the creek and of being able to easily step across the creek in the past.
However, streambank erosion can quickly turn these natural backyard havens into hazards that are unsafe for kids, treacherous for adults and threatening to nearby infrastructure such as sheds, bridges or even houses.
In most instances, streambank erosion is the result of upstream changes in the watershed, such as increased impervious surfaces, channelized stream segments or improperly designed or installed culverts. While a true solution would be to address these upstream causes, such a solution usually lies somewhere between impractical and impossible for a private landowner experiencing streambank erosion.
Hard armoring, such as rip-rap, gabion baskets or walls are not generally recommended, as they often lead to additional erosion downstream or on the opposite bank, are expensive and difficult to install correctly, and negatively impact overall stream health.With that in mind, and recognizing that each situation is unique, here are some general recommendations for preventing and repairing streambank erosion at the site where it is occurring.
1. Don’t Mow, Grow! Maintain a vegetated buffer or “grow zone” along the stream. Forested streamside buffers protect you from the creek, and the creek from you. Generally, mowing should be discontinued within 25 feet of the creek. Fast-growing, aggressively rooting native trees and shrubs should be planted where possible adjacent to the streambanks. These roots help to anchor the soil and hold it in place. Even native grasses, sedges and wildflowers develop far more extensive root systems than standard turf grass. This vegetation should extend as far back as possible from the top of the bank. Examples of trees and shrubs to consider include sycamore, willows, pin oak, silky and gray dogwoods, witch hazel, box elder, choke cherry, and red maples. Recognizing that native species can be difficult to find, LEAPBio and Cleveland Metroparks maintain an online list of regional native plant nurseries here.
2. Relax the Streambank Angle. Actively eroding streambanks are often nearly vertical, or even undercut. Vertical streambanks are very susceptible to further erosion and bank failure such as slumping. Cutting the banks back to a 3:1 slope (or even 2:1depending on space constraints) reduces this risk. Newly-sculpted streambanks should be immediately revegetated with live willow stakes. Additional protection can be provided by anchoring live fascines at the base of the streambank and installing brush mattresses across the face of the streambank (see descriptions below in #4, Bioengineering).
3. Create a Bankfull Bench. If space is available, a bankfull bench can be created in areas where the streambank is being excavated to relax the slope. A bankfull bench is a small, relatively flat floodplain area that provides the creek with an area to store and filter water, and dissipate energy. It should be constructed so that the top of the bench is roughly the same height as the top of nearby sand or gravel bars. It should be vegetated in the same manner as the relaxed streambanks, as described above in #2.
4. Bioengineering. Even if relaxing the streambanks is not possible due to space constraints, or it would require removing infrastructure or large trees to do so, there are many bioengineering techniques still available. Live willow stakes can be installed in the streambank. They will take root, and the roots will help to hold the streambank soil in place, while the branches and leaves slow and divert the streamflow. Live fascines – bundles of willow, red-osier dogwood or sycamore live stakes, or a combination of these – can be anchored to the base of the streambank, where they will root and form a living line of defense against streambank erosion. Live stakes can be installed behind and above the live fascines. These practices also work to improve instream health for fish, amphibians and other animals that depend on the stream for survival. Installation of bioengineering practices is best done in late fall or early spring.
Additional Resources: The Ohio Department of Natural Resources has developed fact sheets for these and other practices as part of their Stream Management Guide series, available online here.
Blog Author: Jared Bartley, Rocky River Watershed Coordinator