|
|
||
 Appendix B: Bioengineering for Streambank Erosion Control -- Guidelines
Indirect Documentation of Erosion Protection
Erosion protection is assumed to be offered by the vegetation if the plants are surviving
and developing; that is covering the site. The development of the vegetation needs to be
monitored and possibly correlated, at least from a visual standpoint to the degree of erosion
or lack of erosion taking place on the treated streambank. One would assume, for example,
that vegetative plantings are doing a good job if the vegetation is growing well in all elevation
zones in the project area and if the stream is not undercutting the treatments, flanking them,
or scouring them to the point of failure.
Aftercare
As mentioned above, early monitoring may mean some early remediation and maintenance
just to ensure long-term viability. What does this early remediation and maintenance mean?
Does this constitute periodic irrigation or repeated fertilizer application? Not as a regular
rule. However, plants should be well watered immediately after planting. Bioengineering
projects are normally installed at a time of the year, such as early spring, where precipitation
is sufficient to allow the planted vegetation to sprout roots and stems and obtain a foothold
in their environment. Or, they are installed in the late fall during dormancy. Repeated
irrigation is not needed then. Hopefully, fertilizer and other soil treatments were applied
before or during planting, if needed, and they should not be required again, unless unusual
circumstances prevail.
Possible aftercare requirements may mean bolstering a particular treatment with additional
plant or even inert materials after an immediate flood event. Flooding may have caused some
plants to wash out before they had a chance to secure themselves with their roots. Hopefully,
engineered materials, such as wire, stakes, geotextile coverings, rock toes, etc. would have
helped hold the plants and soil until the plants become established, but sometimes any one of
these materials, either plants or inert materials, may need bolstering.
Other aftercare measures, as mentioned above, may mean treating plants with an
insecticide or fungicide if insects or disease is widely prevalent. Usually, this will be the
exception rather than the rule. One can overcome widespread insect or disease damage by
emphasizing a wide diversity of plants in the plant mix so that if one species is attacked, the
whole vegetative treatment will not be jeopardized. Beaver and herbivores, such as geese,
may be a problem in some cases by feeding on woody and emergent aquatic plants,
respectively. Beaver will often chew off the upper part of willow and poplar cuttings, but
these can resprout and still perform satisfactorily if the complete cutting or stem is not
chewed off or dislodged. In some cases, where beaver are known to be in the area, then a
trapping program may be advised. Waterfowl, such as geese, like to grub out emergent
aquatic plants as well as feed on the upper parts. Temporary fence corridors made out of
wooden slats with tiered twine attached to the slats have been shown to prevent geese from
feeding on emergent aquatic plants. They do not like to feel trapped inside narrow confines
where they cannot escape quickly.
B-81
|
||
|
||
