Challenges to Streambank Stabilization
Eroding streambanks are a natural occurrence. When dynamic streams are left alone, they constantly change, eroding streambanks and altering the landscape. As we continue to develop our lands, this erosion can be accelerated, threaten public/private improvements, and/or increase the level of pollutants entering the streams. There are many ways to attempt to stabilize a streambank and every streambank must be evaluated to decide which options might be a viable solution.
Quick Fixes with Short Lifespans
Utilization of grouted riprap, loose riprap, and broken concrete slabs have been used for many years and can provide a short-term solution to an immediate threat. Many times, with this type of practice, the eroding bank changes location by moving downstream. It is also not uncommon for the erosion to move upstream, or under the stabilized areas and cause the riprap/concrete to be displaced. This accelerates the erosion that previously existed.
Long-term Solutions
Riprap is one of the most utilized and sustainable long-term solutions if properly engineered. One of the most critical elements of this solution is selecting the right size of rock for the application. Each stream has a different channel velocity that must be determined to select a gradation of rock that will not be dislodged. Proper keying techniques is a critical step as well.
There are several different ways to use riprap to minimize the quantity of material utilized.
Bendway Weirs are a possible riprap solution that should be considered for eroding banks that also have a sharp radius. This solution occasionally calls for heavier design involvement, but typically require less rock than other techniques, thereby reducing material costs. They can also provide the benefit of slowly healing the eroding bank such that it moves the thalweg back to a previous location. (The thalweg is the middle of the channel)
Longitudinal Peak Stone Toe Protection (LPSTP) is another way to utilize riprap to stabilize a bank. This method attempts to stop the undercutting of the toe of the slope thereby allowing the bank to slough off to the critical angle of repose of the bank material, which can then revegetate.
Experience is Critical
The best way to learn is from experience. There is something new to learn from every project. Since 2004, we have utilized these two solutions for several stabilization projects and have had great success. Most projects will require some follow up maintenance, but if done right the first time, it is normally a minor adjustment to the original plan. The pictures shown below are from a project on Center Creek in Jasper County, Missouri completed in 2017. The project included 9 bendway weirs and 350 lineal feet of LPSTP. Now, three years later, the eroding banks have stabilized and the two areas where the weirs were utilized have moved back towards the center of the creek. No maintenance has been done to date. However, there may need to be an adjustment made shortly to one weir as there is some slight erosion between the two most upstream weirs. The goal of this project was to stabilize the banks to reduce the sediment load being washed into the Spring River watershed. The project was partially funded with a Missouri Department of Natural Resources (MDNR) Stormwater Grant. Government agencies who were involved with the project included the Missouri Department of Conservation, MDNR, US Department of Agriculture, and the US Army Corps of Engineers.
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