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Alabama DOT improves dewatering performance of silt fence

News | November 30, 2022 | By:

Using the Auburn University Erosion and Sediment Control Testing Facility (AU-ESCTF) and working on behalf of the Alabama DOT (ALDOT), J.B. Whitman, M.A Perez, W.C. Zech, and W.N. Donald improved the dewatering characteristics of silt fence. They performed structural analysis, design, and assessment of silt fence performance under current practices with a recommended alternative design that improved structural stability, facilitates site dewatering and drying from 24+ hours to four hours, and provides additional storage for subsequent runoff events with less risk of failure. 

Photo courtesy of Michael A. Perez, Ph.D., P.E., CPESC, Assistant Professor, Dept. of Civil & Environmental Engineering, Auburn University – Stormwater Research Facility

The AU-ESCTF allowed full-scale performance evaluations of sediment retention capabilities, water quality impacts, and effluent flow rates.  The recommended alternative design had little to no adverse effect on these performance factors when compared with current practices without dewatering capabilities. 

The design is easy to construct with minimal training and uses routinely available materials, board(s) to construct a dewatering board(s) with a weir, riprap and geotextile for outfall(s) and additional steel post for structural stability.  This design can endure through the life of a construction project and requires less guesswork than other complicated dewatering schemes.

ALDOT’s Richard Klinger, environmental construction engineer, embraced the new design and worked to develop a Standard Specification (665608) released in 2021. When asked why the design revisions were important, Klinger responded, “ALDOT strives to continuously improve our erosion and sediment control practices to keep pace with the ever-evolving environmental regulations. Our silt fence practice, at times, is our last line of defense and must be as strong as practicable while maintaining a high level of water quality.  The modified silt fence design, with reduced height, requires less material which is more environmentally friendly while delivering increased performance. 

“At times, field conditions may differ from the design, or an issue with the grading operation may cause unintended impoundment of the silt fence,” he continued. “The increased post spacing and the dewatering weir are utilized as a maintenance measure for these areas of unintended impoundment. The additional posts and dewatering weir can be installed in the existing silt fence without jeopardizing the structural integrity of the fence or having to completely remove sections and reinstalling. The dewatering weir is simple to construct, easy to install, and gives the contractor the ability to get back to work in these areas much quicker than with previous practices.”  

“This is just one of many examples where ALDOT’s investment in Auburn’s research continues to pay off,” added ALDOT’s Wade Henry, assistant state design engineer. “ALDOT is committed to continue to learn and practically apply that knowledge to evolve our erosion prevention best management practices so that we can address erosion in the most effective and efficient ways possible.”

If you would like to learn more about the innovative dewatering silt fence, the research report may be found in the ASCE Library.  If you have any questions you may contact the ALDOT’s Mr. Richard Klinger, Environmental Construction Engineer, Mr. Wade Henry, Assistant State Design Engineer, or Dr. Michael Perez, Auburn University.  One may also contact FHWA’s Mr. Brian Smith, Ecologist.

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