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 Appendix B: Bioengineering for Streambank Erosion Control -- Guidelines
The tree species also become taller and more massive. Trees are noted for their value in
stabilizing banks of streams and rivers (Seibert 1968; Leopold and Wolman, 1957; Wolman
and Leopold, 1957; Lindsey et al. 1961; and Sigafoos 1964). The trees have much deeper
roots than grasses and shrubs and can hold the upper bank together. The banks of some
rivers are not eroded for durations of 100 to 200 years because heavy tree roots bind the
alluvium of floodplains (Leopold et al. 1957; Wolman and Leopold 1957; and Sigafoos 1964).
A combination of trees, shrubs, and grasses in this zone will not only serve as an integrated
plant community for erosion control, but will improve wildlife habitat diversity and aesthetic
appeal.
Bioengineering Treatments
The entire streambank should be treated to furnish a maximum array of plants capable of
providing proper ground cover and root penetration for erosion protection, wildlife habitat,
water quality improvement, and many other benefits. At times, the planting sites or zones
may be quite narrow in width or difficult to distinguish depending on the geomorphology of
the stream. The entire bank in these cases should be treated as a systematic arrangement of
plants and treatment practices.
Toe Zone
This is the zone that will need to be protected from undercutting with treatments such as
stone or rock revetments, gabions, lunkers, log revetments, deflector dikes, cribs, rock and
geotextile rolls, root wads, or a combination of materials. The zone rarely has vegetation
employed in it alone, but when vegetation is employed, it is used in combination with
materials that extend below the normal flow of water and above it. The principle is to keep
high velocity currents from undercutting the bank either through armoring the bank or
deflecting the currents away from the site of concern. Vegetation can then be used either
above the armor or in between and above the deflecting structure.
Stone or rock revetments in a bioengineering application are used at the toe in the zone
below normal water levels and up to where normal water levels occur. Sometimes, the stone
is extended above where normal flow levels occur depending on the frequency and duration
of flooding above this level. Then, vegetation is placed above it in a bioengineering
application. Stream guage information helps in making this judgement. Unfortunately, there
are no set guidelines for how far up the bank to carry the revetment except to say that it
should be applied below the scour zone up to at least the level where water runs the majority
of the year. Engineering Manual 1110-2-1601, Change 1 (Corps of Engineers, 1994) gives
guidelines for riprap toe protection.
One such rock revetment for toe protection was used in conjunction with vegetation
above it on Crutcho Creek, Tinker Air Force Base, Oklahoma (Figure 7). In this example,
the creek is flashy and often reaches or exceeds the top of bank during the spring of each year
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