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 Vegetative Methods for Erosion Protection
Many streambank protection projects include vegetation without conscious thought
by the designer, since native vegetation often establishes itself once the processes of bank
failure are stopped by structural means. However, if the potential for utilizing vegetation is
considered from the beginning, then the effectiveness, environmental aspects, and economy
of a project can often be significantly improved.
The general principles of erosion protection discussed in Chapter 6 are fully applicable
to vegetative work. In fact, because vegetative works are generally more vulnerable than
structural works, particular care must be taken to insure that the overall approach is sound.
Beyond those general principles, the details of successful use of vegetation are even more
site-specific than for structural bank protection. The terminology of the details can sometimes
be confusing, because the technology developed somewhat independently from region to
region over a long time period, whereas widespread interdisciplinary interest in the subject,
and broad dissemination of the technology, is fairly recent. Also, the many variations on the
basic techniques add some confusion to the terminology. However, the basic concepts are
straight-forward, and have international and timeless application.
9.1.2 ADVANTAGES
The two obvious advantages of vegetation as erosion protection are its environmental
attractions and its relatively low cost. A third and less obvious attraction is that it can
increase the safety factor of structural protection by enhancing the level of performance.
Because many types of vegetative treatment are labor intensive, the cost advantage will be
especially prominent in regions where labor is inexpensive, skilled in agriculture, and
conscientious.
9.1.3 DISADVANTAGES
Some characteristics which make vegetation effective and desirable in most situations
may be disadvantages in other situations. However, many of the following concerns will
either not be applicable for a specific project, or will be acceptable as compromises in light
of vegetation's merits.
The most serious shortcoming is that even well executed vegetative protection cannot
be planned and installed with the same degree of confidence, or with as high a safety factor,
as structural protection. This is not to say that vegetation will not be adequate, or will not
be more cost effective than structural protection in a specific situation, but is rather an
acknowledgement that structural protection can be designed to function under more severe
conditions of hydraulic and geotechnical instability than can vegetation. Vegetation is
especially vulnerable to extremes of weather and inundation before it becomes well
established.
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