Selection of Site-specific Stabilization Techniques
entire riparian corridor is wooded, though, then neither stabilization work nor
continued erosion of the bank would have significantly impacted the character
of vegetation adjacent to the streambank. However, if the adjacent land was
agricultural, with only a narrow band of native riparian vegetation, then
continued erosion would have destroyed that native vegetation. A positive
effect of bank protection work could then be claimed, even if some
destruction of streamside vegetation accompanied it, particularly if the bank
was revegetated with environmentally beneficial plants as part of the work.
However, woody vegetation felled by erosion would have provided aquatic
food and cover, which will no longer be the case once the bank is stabilized.
Aquatic cover can be deliberately added as part of the work, but still the bank
substrate is irretrievably altered by the work, as is the input of organic
material from fallen vegetation. An ironic climax is sometimes reached when
the land adjacent to the stream is developed for man's use once the threat of
channel migration is removed.
Indirect protection methods may not change aquatic and terrestrial habitat
initially, and often can be considered to improve aquatic habitat initially by the
provision of cover and diversity of hydraulic conditions. However,
subsequent deposition may destroy some or all of the "improved" aquatic
habitat, but the vegetative growth which accompanies the deposition provides
terrestrial habitat and a source of organic material. If the deposition becomes
relatively flood-free, though, clearing for agriculture may follow, with the end
result in extreme cases being the conversion of aquatic habitat to agricultural
land.
Dealing with these complexities is best approached by classifying potential impacts,
either temporally or by type of impact. One valid approach to the selection of preferred bank
stabilization methods is to classify potential impacts into the following categories:
Aquatic wildlife habitat;
Terrestrial wildlife habitat;
Recreation;
Aesthetics; and
Cultural resources.
5.2.1.1 Aquatic Wildlife Habitat
Aquatic habitat may be improved or damaged by bank stabilization work. Potential
impacts are as follows:
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