There are two terms used for engineering for stream banks. First, there is Soft Bio-engineering and then you have Hard engineering. The body of water and the type of erosion and other factors for consideration will help you decide which method to use and on occasion you may need to apply both methods. The Lewis & Clark Conservation District is more than happy to assist you with questions, put you in contact with the right people, and of course before any work begins you will need to obtain a permit.
Soft Bio-engineering Methods
Bio-engineering, biology and engineering come together through an array of techniques that temporarily stabilize soil until biological protection, such as roots and branches, can take over. Bio-engineering combines both the physical science and hydraulic principles with botany and aquatic biology to then implement design for both physical and living environments. Floodplain vegetation slows lateral movement and reduces overbank flood velocities (Montana Stream Permitting, 2001).
There is no set way to preform a bio-engineering project however, there are some key aspects and questions to ask that will lead you to success when implementing these techniques (see the Montana Stream Permitting Book for questions to ask). You have many considerations to take into account and they are all dependent on the natural body of water you need to do work on, the surrounding vegetation, and the type of erosion. An increasingly common practice used here in Montana is a willow soil lift. Stabilizing a bank through the use of conifer fancies, natural geotextile erosion control fabrics, and willow lifts. The willows must be dormant and native to the area when performing these projects to eliminate the transportation of invasive species. As far as cost goes, this method is extremely cost efficient and competitive with other methods. Willow soil lift projects are highly effective when executed properly and are a natural approach to protecting your land.
Hard Engineering Methods
There are many hard engineering methods, and again there is no set way to perform these methods. The goal when performing streambank restoration is to use Best Management Practices (BMPs) and to really understand the type of stream you are working with. A common hard engineering method used around the country is Rip-Rap. Rip-Rap should ONLY be used if the body of water has high flow rates and you need long-term durability. It is very hard for vegetation to become established within rocks and therefore this method should only be used if there aren’t other effective alternatives.
Methods in Combination
Is a rock-toe necessary? Sometimes, but not always. Can the flow of the stream work with bio-engineering? Depends. Can you integrate rock-tows and bio-engineering? Absolutely, but again it is dependent on the body of water you are working on. Is instability systemic or localized? If the stream or creek has a rocky substrate then you might want to begin with a rock-tow and add the willow lifts. If the substrate is smooth then you do not want a rock-toe.