Vegetative Methods for Erosion Protection
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 that 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.
Vegetative treatments often require significant maintenance and management in order
to prevent the following problems:
Growth of vegetation causing a reduction in flood conveyance or causing
erosive increases in velocity in adjacent unvegetated areas.
Deterioration of the environmental function of the vegetation due to
mismanagement by adjacent landowners, vandalism, or natural causes.
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.
Roots infiltrating and interfering with internal bank drainage systems, or
causing excess infiltration of water into the bank.
In arid regions, vegetation's ability to reduce soil moisture 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. In any
event, a riparian strip of vegetation is not likely to harm the groundwater
resource enough to outweigh the positive values of the vegetation.
Many of these problems may be avoided through selection of the appropriate
type, and species or clone 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.
9.1.4 TYPICAL APPLICATIONS
Vegetation is most often used in conjunction with structural protection. Exceptions
may be made for very small waterways, for areas of low erosion activity, or for situations
where the consequences of failure are low and there is provision for rehabilitation in case of