Earlier this year, Jake Tomlinson with Penn State’s Center for Agricultural Conservation Assistance Training presented a session on streambank stabilization and what implementation of it looks like on the farm.
Stream erosion is naturally occurring, though sometimes expedited by certain stressors. The stream body is either in a state of equilibrium (the stream erosion is being equally distributed and the water flow is normal) or disequilibrium (the stream body is experiencing excessive erosion in certain areas and excessive sedimentary collection in others) at all times.
Erosion can be caused by several factors. The slope and depth of the stream can increase its erosive power. Disconnection from the floodplain can increase water velocity, leading to erosion of the stream bed and the embankment. This disconnection can be triggered by altered channels (building structures, roads and other diversions obstructing water flow), animal traffic and increased frequency and intensity of storms.
It’s helpful to know how all of the components of the stream’s system work together. The baseflow is the lowest elevation of flow; the bankfull is the elevation at which the primary stream body is filled with water. The flood plain is the immediate field area next to the bankfull boundary.
Understanding all of these components is valuable to diagnosing stress points more susceptible to erosion. Implementing grade controls and armoring for the bed and bank structures (tree planting and implementation of other vegetation growth, for example) can fortify these stress points and increase resistance to erosion.
There are several biological and economic benefits that arise from erosion mitigation. It can decrease nutrient and pollutant pooling. It can protect and restore riparian habitat – and improve animal health. Improved water flow will reduce sediment accumulation at points of stress. Mitigation efforts can lessen the impact of flooding events. It can help protect property and allow continued access for both humans and livestock over a long time.
Building an action plan requires careful planning. “We can’t just fire up the dozer,” Tomlinson said.
The root cause of the issue(s) must be identified. Biological factors must be catalogued: water quality, stream classification, instream habitat, etc. Regulations must be studied – what regulations are going to drive the kind of restoration and conservation work the landowner is looking to accomplish.
Tomlinson noted several tools that are helpful in assessing stream conditions, like the EPA’s “Rapid Bioassessment Protocols for Uses in Streams and Wadeable Rivers.”
Beginning with stream crossings as a mitigation effort: “Their purpose is to limit animals’ access to the riparian corridor and to prevent congregation, both of the animals themselves and the pooling of nutrients and other inputs,” Tomlinson explained.
Streambank stabilization provides myriad benefits to landowners, livestock and local wildlife. Photo by Courtney Llewellyn
Stream crossings have many benefits, ranging from providing continued access to all fields and pastures to improved animal health and quality to improved stream health and continued passage for fish and aquatic organisms.
There are three types of crossings: the ramp (one side’s approach is stabilized to allow access to the body of water), the ford (stabilized approaches on both sides and stabilization/reinforcement through the streambed where necessary) and the culvert/bridge (typically in high traffic contexts).
There are several design considerations when approaching construction: the purpose and location of the stream crossing; the consistency/structure of the stream bed; the watershed size; the bankfull dimensions; and more. Those factors will steer what kind of crossing structure is appropriate.
Streambank stabilization efforts can be a little more complicated.
The deflector is a large triangular structure, anchored in the streambank, that provides localized stabilization. It is positioned 30º upstream and 60º downstream and is one-third of the channel width. There are multiple types of deflector: the stone or sawtooth deflector, the log-framed deflector (the stone is reinforced with several logs), the root wad deflector (comprised of various mature trees and their root balls) and the log vane (comprised of several pinned logs).
The rock vane and J-hook system is constructed entirely out of rock and comes in handy in larger stream bodies with greater energy levels. Its unique J-shaped structure creates a plunge pool at the center of the channel which is great for the native aquatic life. The modified mud sill uses logs to help secure the face of the embankment – perfect for streams with steep, eroded banks. It’s unique in that it can be used in a straight or curved flow.
The root wad barricade is an extended network of several connected root systems providing immediate, stable protection while also creating habitat for local wildlife and insect life. The cross vane is typically constructed from stone or logs and traverses the full width of the channel. It is ideal for providing grade control for crossings, cross pipes or incised channels.
Tomlinson also mentioned some “newer work that’s going on out there,” such as the large wood addition, which uses root wads and whole trees to provide stability. He noted, “If a source of trees is onsite, this method can be very cost effective.”
The “chop-and-drop” large wood addition is useful in headwater systems – but not often practical for pasture or cropland.
Lastly, the rip rap shotgun, a structural practice, provides stability through several different elements, typically protecting infrastructure such as homes, businesses, bridges, etc.
The design considerations mirror those of stream crossings. What are you trying to accomplish? What are some of the biological concerns? What are the minimum design standards that need to be met to meet and access financial assistance thresholds and permitting requirements?
Financial assistance for streambank stabilization is available and typically varies depending on the structure’s size and the extent of the project. Permitting varies by state.
Technical and financial assistance is available through a variety of avenues, covering everything from design consultation to local permitting needs. Look to local county conservation districts, NRCS and/or nonprofit NGOs like Trout Unlimited.
by Andy Haman
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