Selection of Site-specific Stabilization Techniques
5.2.2.1 Preserve or Improve Wildlife Habitat
As with aesthetics, natural conditions may be viewed as the optimum habitat
condition, and as a general concept, work which disturbs natural conditions the least would
be favored. However, the degree to which various methods alter existing conditions, and
whether the alterations are desirable or not, depends to a great extent on specific geomorphic
and biologic site conditions. Still, the following concepts will be generally applicable to the
selection of a bank protection method:
Diversity is preferable to a more sterile, uniform environment, whether the
diversity be natural or created by man, as long as critical habitat types are
present (Henderson, 1986).
Armoring the streambank usually changes stream geometry and hydraulics less
than indirect protection, but alters the morphological characteristics and
environment of the bank more, removes more terrestrial and aquatic cover,
and provides less diversity. However, stone armor does provide valuable
substrate for many benthic organisms, and provides micro-cover for fish,
especially if the range of stone size in the specified gradation is large.
Deposition within the interstices of some armor materials may to some degree
replace in kind the natural bank material.
A "hybrid" or "zoned" approach where different armor materials are used for
different elevations on the bank, depending upon the streamflow
characteristics and bank erodibility, with vegetation usually being the upper
slope component, offers environmental and aesthetic benefits as well as
economy.
Indirect protection techniques leave much of the stream bank undisturbed,
although by definition, erosion must eventually cease, and deposition will
occur in some areas, thus the ultimate condition will unavoidably be altered
to some degree. The aquatic habitat provided by the structure itself and by
induced vegetation, and the terrestrial habitat provided by induced vegetation
will often be superior to natural cover.
Vegetation is almost universally considered to improve both aquatic and
terrestrial habitat conditions, although its value and suitability is highly
site-and-species specific. It can be used with almost any protection technique.
Providing geotechnical stability by placing fill against the bank, retained with
a structure of some type, will disturb less terrestrial habitat than excavating
the bank to a stable slope, although the cost may be greater. However, the
lower part of the structure will disturb some aquatic habitat, although this may
be offset by specifying a "borrow" area configuration which creates new
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