Appendix B: Bioengineering for Streambank Erosion Control -- Guidelines
Bioengineering projects need to be observed early after project construction for signs of
plant survival and development, as well as for streambank integrity. At least qualitative
monitoring should be done to assure that detrimental phenomena do not jeopardize the
project. For instance, Court Creek, Illinois, one of the project case studies discussed in
Volume II, had an infestation of spider mites. Within a month or so after planting, spider
mites had damaged almost all of the leaves on the willow that were being used for
stabilization. Without remedial spraying, project failure could have resulted. In another case
study, North River, Massachusetts (Volume II), a drought occurred the first year after
planting and killed much of the planted emergent aquatic vegetation. Remedial planting had
to be done the following year to compensate for drought mortality. Also, along with
vegetative development, streambank integrity needs to be observed to ensure that unraveling
of the bank is not occurring from such actions as undercutting of the toe or flanking at the
upper or lower ends of the treated section. If this is occurring, then corrective measures need
to be taken immediately, such as placing more rock or some other hard structure in those
places. Projects should be monitored at least a couple of years after development at a
minimum. Preferably, they should be monitored through 1-2 flood events where currents are
directed on the treated bank. One can then assess whether the site remains stable or unravels.
In the latter case, remediation can occur. Site monitoring in bioengineering projects should
be written into the contract specifications so that early remediation does not become a part
of operational and maintenance costs, which often have to be budgeted separately within
many agencies.
Direct Documentation of Erosion Protection
Aerial Photographic Monitoring. Each bioengineering reach and associated treatment,
e.g., rock toe with brush matting, vegetative geogrid, should be monitored for erosion directly
by use of aerial photogrammetric techniques. This will allow evaluation of changes occuring
at the land-water interface providing the procedures discussed below are used.
Aerial photo coverage should be flown at least twice a year for the first 2-3 years or
immediately after a flood event. Suggested times are in the spring and in the fall. Low-water
periods are preferable. Photo flights should be highly controlled; that is, the scale of repeated
flights must be the same. A suggested scale is 1:1,000. Also, three ground control points of
known location and dimensions should be used per frame to provide accurate
photogrammetric measurements and these should be orthogonally corrected when processed
to negate distortion. Recommended film type in priority order is: (1) color infrared and (2)
color. To allow comparisons of repeated photo coverage, flights must be made during low
water periods and when river water levels correspond to each other; that is, at or below
previous photographic periods. Overlays can be made on the photos which will delineate the
water-interface boundary. Subsequent overlays can be compared showing any changes in the
water-interface boundary (see Figure 44). Photographic measurements can then be made on
the overlays to determine amount of surface area lost to erosion.
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