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Appendix B: Bioengineering for Streambank Erosion Control -- Guidelines
Monitoring and Aftercare
Most importantly, monitoring and necessary aftercare must be a part of any
bioengineering design and must be included in the plan of development and the
implementation stage. The intensity and frequency of monitoring and aftercare will depend
on site conditions, such as harshness of climate, probability of animal disturbance, high wave
or current conditions, etc., and on established success criteria.
On many sites, it is essential to protect plantings from damage by animals, such as Canada
geese (Branta canadensis), or beaver (Casta canadensis) and other mammals. The use of
irrigation may be required during aftercare and will improve growth and survival of plantings
that are installed during dry seasons and in dry soils. The decision about irrigation must be
made based on economics contrasting the need to irrigate with the cost of possible mortality
and the consequences of failing to obtain the desired erosion control and other functions. See
Part IV for more detail on monitoring.
Hard Structures and Bioengineering
Generally speaking, bioengineering is considered "a soft fix." This is not necessarily the
case. On first or second order streams, the sole use of vegetation with perhaps a little wire
and a few stakes for holding the vegetation until it is established makes bioengineering more
of a soft treatment. However, bioengineering is used also in combination with hard
structures. These hard structures are used to protect the toe of the bank from undercutting
and the flanks (ends of treatment) from eroding. The larger the stream or stronger the flow,
the more probable that hard structures will be incorporated into the bioengineering design
model. This is also true when risks become greater, such as when an expensive facility is
being threatened. As an example, a utility tower along a stream in Georgia1 was being
threatened by erosion. A rock revetment had previously been used in front of the tower, but
was washed out. A bioengineering treatment that incorporated live willow whips and a log
crib were installed to control erosion. Crib logs controlled undercutting and flanking while
the live willow whips installed between the log stringers developed and strengthened the
overall structure and gave it a "green" appearance.
In most of the case studies presented in Volume II, and in the references made to other
bioengineering streambank erosion control, hard structures such as rock riprap, log/tree
1
Ms. Robin Sotir, personal communication, President, Robin Sotir and Associates,
Marietta, Georgia
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