Selection and Design of Channel Rehabilitation Methods
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.
Quantitative guidance for the use of vegetation in streambank protection is limited, although there
has been progress through recent research. Most vegetative measures have constraints on the season of
the year in which installation can be performed. This shortcoming can be mitigated to some degree by
advance planning or by developing more than one option for vegetative treatment.
In arid regions, vegetation can reduce soil moisture which may be a concern. However, this is not
likely to be a serious concern if the native plant ecosystem was considered in the initial selection of
vegetative species.
Vegetative treatments often require significant maintenance and management to prevent the
following problems:
Growth of vegetation causing a reduction in flood conveyance or causing erosive increases
in velocity in adjacent unvegetated areas;
Trunks of woody vegetation or clumps of brushy vegetation on armor revetment causing
local flow anomalies which may damage the armor;
Large trees threatening the integrity of structural protection by root invasion or by toppling
and damaging the protection works, or by toppling and directing flow into an adjacent
unprotected bank; and
Roots infiltrating and interfering with internal bank drainage systems, or causing excess
infiltration of water into the bank.
Many of these problems may be avoided through selection of the appropriate type, and species
of vegetation for the purpose. However, designers rarely have the practical experience or formal training
in biotechnology to make such selections and expert advice must be obtained from qualified individuals in
plant biology and bioengineering.
6.2
GRADE CONTROL
Implementation of bank stabilization measures without proper consideration of the stability of the
bed can result in costly maintenance problems and failure of structures. The stability of the bed is an
essential component of any channel stabilization scheme. Bank stabilization measures are generally
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