Stream Restoration and Soil Bioengineering

Angela Akridge, P.E., Joseph D. Eigel, Ph.D., P.E., and J. George Athanasakes, P.E.

The concepts of clean water and a green environment in a growing community are central to the Louisville and Jefferson County Metropolitan Sewer District's (MSD) vision of putting its customers first. Making the vision a reality means restoring the function and value of streams in Kentucky's largest urban area. To do this, MSD has implemented a policy that makes stream restoration through natural channel design and soil bioengineering the preferred way to protect streambanks and slopes across Jefferson County.

Natural channel design considers the function and stability of natural streams and their floodplains. Successful designs ensure that the system is healthy, productive, and sustainable. Soil bioengineering techniques are used within natural channel designs to stabilize and re-vegetate streambanks and to enhance habitat.

Soil bioengineering uses living plant material to stabilize streambanks and unstable slopes.  Soil bioengineering installations are designed considering soil characteristics, the stream's physical structure, hydrologic conditions, and climate. Soil bioengineering reduces erosion control maintenance costs, improves wildlife habitat, helps restore the function of riparian ecosystems, and improves stream aesthetics.

Native plant species that thrive along streams develop deep roots that reinforce the soil that forms streambanks. Their foliage provides resistance that lowers flow velocities, thus reducing shear stresses on the bank. As flows rise and foliage bends over, it acts to armor the soil surface. Foliage also provides shade to keep streams cool and provides food and shelter for waterfowl, mammals, and amphibians living along the stream. Rocks and boulders placed in the streambed create riffles that provide habitat for macroinvertebrates, a vital component of the food chain, and induce turbulence that aerates the stream, raising dissolved oxygen levels that are critical for fish survival.

Soil bioengineering techniques apply to a wide range of projects, from repairing an isolated bank failure to completely restoring a stream where natural meanders, riffles, and pools are created following the principles of fluvial geomorphology. Fluvial geomorphology deals with the interactions and processes that affect the flow of water across the earth. Depending upon the site, major stream restorations may not be practical on every urban stream segment. In those situations, soil bioengineering can provide significant habitat and water quality improvements.

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