Stabilizing Stream-Bridge Crossings with Soil Bioengineering Techniques: A Texas Department of Transportation Demonstration Project

This paper documents the design process of streambank soil bioengineering demonstration projects in a research project sponsored by Texas Department of Transportation (TxDOT). During 1998 and 2002, Texas Transportation Institute was conducting the research project with a task of designing several streambank soil bioengineering projects. A total of 22 bridge and stream crossings in 9 TxDOT districts were visited and assessed. Rarely did the research team observe that streams were in dynamic equilibrium if bridge structures severely interfered with the streams. Numerous streambank failures were observed and modes of failure were categorized. The research team concluded that most streambank failures can be attributed to the treatment of the edge between the built and natural environment. Failure sites almost always have rigid treatments such as concrete riprap on the boundary between the bridge structure and the stream. Fixed, rigid edges severely limited any self-adjustment of the stream to respond to the flow energy, and therefore, often failed. Soil bioengineering offers an alternative to “soften” the edge between built and natural environment. This paper provides lessons to transportation professionals from the research team’s experience in assessing streambank failures, analyzing failure causes and modes, designing demonstration projects, and monitoring the built streambank project.