Learning from streambank failures at bridge crossings: A biotechnical streambank stabilization project in warm regions

In a biotechnical streambank stabilization project, researchers visited and assessed 22 bridge and stream crossings in east half of Texas of the United States. Researchers rarely observed streams in dynamic equilibrium if bridge structures severely interfered with the streams. Numerous streambank failures were observed and documented. A primary problem noted was the treatment of the edge between the built and natural environment. Failure sites almost always have rigid treatments such as concrete armor on the boundary between the bridge structure and the stream. Such a fixed, rigid treatment could not allow any self-adjustment of stream dimension or profile, which in turn resulted in failures on the bridge structures including piers and abutments. Biotechnical engineering offers an alternative to treat the edge between built and natural environment and provide a buffer to absorb erosive forces from the flow onto built structures. While these techniques are often used in the cooler areas of the United States, there are significant challenges to the application of this technology in warm regions, specifically in the Plant Hardiness Zones 8–10 defined by the U.S. Department of Agriculture. It is primarily because short dormant periods in warm regions restrict the construction period for implementing the live cutting technique, an important method in biotechnical engineering.This paper describes a streambank stabilization project implemented in Texas of the United States, where the research team assessed and analyzed streambank failure causes at bridge crossings in warm regions, and addressed warm region construction issues encountered during the project. The paper further discusses the design process, implemented result, and monitoring of the built biotechnical streambank stabilization project.