The major factor affecting species selection is the length of time required for the plant to
become established on the slope.
Water-tolerant grasses such as canarygrass (Phalaris), reedgrass (Calamagrostis), cordgrass
(Spartina), and fescue (Festuca) are effective in prevent erosion on upper banks which are
inundated from time to time and are primarily subject to erosion due to rainfall, overland flow,
and minor wave action. Along the lower bank, where erosive forces are high, grasses are
generally not effective as a protective measure; however, cattails (Typha), bulrushes (Scripus),
reeds (Phragmites), knotweed and smartweed (Plygonum), rushes (Juncus), and mannagrass
(Glyceria) are helpful in inducing deposition and reducing velocities in shallow water or wet
areas at the bank toe and in protecting the bank in some locations. Willows (Salix) are among
the most effective woody plants in protecting low banks because they are resilient, are
sufficiently dense to promote deposition of sediment, can withstand inundation, and become
established easily.
Grass can be planted by hand seeding, sodding, sprigging, or by mechanical broadcasting of
mulches consisting of seed, fertilizer, and other organic mixtures. Several commercial
manufacturers market economical erosion control matting that will hold the seed and soil in
place until new vegetation can become established. The matting is generally installed by hand
and secured to the bank where plantings have been made to prevent erosion, then a fence
should be placed along the top of bank. If livestock require access to the stream for watering
or crossing, gates should be placed in the fence at locations where the cattle will do the least
amount of damage to the planted bank; additionally, crossings should be fenced.
6.6.2 Bioengineering Countermeasures
The past few decades have seen increasing use of vegetation as a bank stabilizer. It has
been used primarily in stream restoration and rehabilitation projects and can be applied
independently or in combination with structural countermeasures. The term bioengineering
and is generally used to describe stream bank erosion countermeasures and bank
stabilization methods that incorporate vegetation.
Stabilization of eroding stream banks using vegetative countermeasures has proven
effective in many documented cases in Europe and the United States. However, the use of
bioengineering with respect to scour and stream instability at highway bridges is a relatively
new field. There is research being conducted in these fields, but these techniques have
generally not been tested specifically as a countermeasure to protect bridges in the river
environment.
Bioengineering erosion control is not suitable where flow velocities exceed the strength of
the bank material or where pore water pressure causes failures in the lower bank. In
contrast, bioengineering maybe suitable where some sort of engineered structural solution is
required, but the risk associated with using just vegetation is considered too high.
Nonetheless, this group of countermeasures is not as well accepted as the classical
engineering approaches to bridge stability.
Design of bioengineered countermeasures to minimize rates of stream bank erosion requires
accounting for hydrologic, hydraulic, geomorphic, geotechnical, vegetative, and construction
factors. Although most of the literature dealing with biotechnical engineering on rivers is
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