Biotechnical engineering as an alternative to traditional engineering methods: A biotechnical streambank stabilization design approach
Introduction
In the US, traditional streambank stabilization applications such as channelization and hard-armoring techniques have been preferred as best standardized practice. Channelization reduces the meander of a stream channel to minimize the natural erosion process. Hard-armoring methods, such as stone riprap, concrete pavement, rock gabions, bulkheads made of steel, concrete or aluminum, sack revetments, asphalt mixes, and jetties, reinforce streambank shear strength (Keown, 1983). Many governmental agencies favored stone or concrete riprap because over time, a high degree of precision and confidence in construction has developed from research and analysis. In engineering viewpoints, these methods have been successful for their immediate protection of properties or infrastructure adjacent to the stream after projects were completed.
What was thought successful in the past is being re-evaluated in context of impacts resulting from excessive and rapid urbanization, and public awareness of these new environmental issues. Increasing failures of traditional channelization and armoring methods are generating questions as to whether traditional practices are appropriate in every setting. One specific situation that almost always guarantees a failure is the use of hard armoring only around bridge abutments and streambanks, upstream and downstream of a bridge. Fig. 1 demonstrates an occurrence of failure resulting from this type of situation. Concern about traditional methods increased in the 1970s. The interest in natural techniques called biotechnical engineering was raised, and the benefits and advantages of biotechnical engineering were gradually re-examined (Riley, 1998).
An assessment of failures reveals that many natural stream components critical to ecological benefits are removed when channelization and hard armoring take place. Pools, riffles, point bars and flood plains critical to riparian and aquatic habitats are diminished or eliminated when streams are straightened (see Fig. 2). Straightening channels increases velocity, and hard armoring removes vegetation that can cool water temperature, all of which makes it difficult for fish to survive. Detailed consequences and impacts on stream biota were summarized by Simpson et al. (1982). Those impacts include loss of riparian habitat, reduced diversity, loss of fish habitat, influence on fish reproduction process, etc.
In addition to the loss of ecological benefits, traditional methods may transfer scouring and erosion problems to another area of the stream, rather than heal the entire stream. Traditional methods are typically “point-focused” solutions that concentrate on exact areas that exhibit problem symptoms. These methods attempt to isolate a stream’s form from its process with the use of channelization or hard armoring. This method can conversely lead to violent interactions between form and process, such as excessive erosion and deposition. A stream’s dynamic equilibrium function is disrupted when traditional methods are used to force unnatural conditions on a stream and separate the stream’s physical form and the fluvial process. Channelization minimizes stream sinuosity and hard armoring reduces bank roughness, both of which eliminate a natural stream’s ability to dissipate flow energy, resulting in more serious erosion downstream.
The purpose of this study, was to investigate biotechnical streambank stabilization as an alternative to traditional engineering practice. The objective was to identify biotechnical techniques that can complement traditional engineering method’s weaknesses, and evaluate such techniques in their applicable conditions, cost, strength and limitations.
Section snippets
Identification of strengths and weaknesses of various streambank stabilization approaches
A stream is a complex system. A holistic approach to stream problems that incorporates knowledge from multiple disciplines and identifies strengths and weaknesses from different perspectives can create better solutions (FISRWG, 1998). The authors reviewed disciplines such as hydraulic and geotechnical engineering, fluvial geomorphology, hydrology, biology, ecology, botany, and landscape architecture for their contributions to streambank stabilization practices. From this review, the authors
Traditional engineering in streambank stabilization
Traditional methods employ conventional know-how to secure a streambank. While this practice is workable and has, over time, become easy to reproduce, it has not proven to be the best solution. One primary goal of traditional channel design is to produce a stable channel, which means the channel never changes its plan form and cross-sections (Lane, 1954). The purpose of this goal is often to protect existing properties or infrastructure near streams. However, problems resulting from increased
Conclusion
Measuring the success of a streambank stabilization project is an obscure task at best. In the context of traditional streambank stabilization methods, success is achieved through a singular emphasis on controlling the stream. Where we’ve tried to exert control without understanding the mechanisms at work, detrimental effects have manifested themselves in costly repairs, retrofitting projects, and erosion occurring elsewhere on the stream. Fluvial geomorphology shows promise and improvement
Acknowledgements
This study was part of the research project on “Regional applications for biotechnical methods of streambank stabilization in Texas” funded by the Texas Department of Transportation.
Ming-Han Li is an Associate Transportation Researcher for the Environmental Management Program of the Texas Transportation Institute (TTI). He has a multi-disciplinary education background, including a BS in agricultural engineering from National Taiwan University, an MS in civil engineering from the University of Texas, Austin and an MLA from Texas A&M University. Mr. Li’s research interests are in biotechnical engineering, hydraulics, hydrology and landscape ecology. Mr. Li is also a Lecturer
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Ming-Han Li is an Associate Transportation Researcher for the Environmental Management Program of the Texas Transportation Institute (TTI). He has a multi-disciplinary education background, including a BS in agricultural engineering from National Taiwan University, an MS in civil engineering from the University of Texas, Austin and an MLA from Texas A&M University. Mr. Li’s research interests are in biotechnical engineering, hydraulics, hydrology and landscape ecology. Mr. Li is also a Lecturer in the Department of Landscape Architecture and Urban Planning at Texas A&M University.
Karen E. Eddleman is a Research Associate for the Environmental Management Program of TTI. She holds a BA in English from Texas A&M University. Ms. Eddleman’s training in research techniques, technical writing, and technical editing enables her to contribute a broad range of skills to the research efforts undertaken by the Environmental Management Program of TTI. In addition to streambank stabilization, Ms. Eddleman has research experience in stormwater quality, erosion control, the public participation process for highway projects, and other areas related to the environment.