Appendix B: Bioengineering for Streambank Erosion Control -- Guidelines
Brush layering (branch packing) was used successfully on the Little Patuxent River in
Maryland (Figure 30). There, it was used in combination with live facines (wattles) and live
pegs (Bowers, 1992). Rock riprap was placed at the toe of the streambank for added
protection. Bowers (1992) reported that the top growth of the live facines, live branches in
the branch layering, and live pegs (live stakes or cuttings) provide coverage of and protect
the streambank during storm events. The species used included black willow and silky
dogwood. Branch layering and live facines were used in the low energy zones of the river,
i.e., along the beginning and end of outside meanders. For the areas where the thalweg came
in contact with the streambank on the outside of the meander, root wads were used for
protection and stabilization (Bowers, 1992).
Vegetative geogrid. This is a system that can be used in the splash zone and actually
extend further up the bank into the bank and possibly terrace zones. The system is sometimes
also referred to as "fabric encapsulated soil." It consists of successive walls of several lifts
of fabric reinforcement. In between the lifts are placed 5- to 10-ft long live willow whips.
This system is described by Miller (1992) and was used successfully on Acid Brook in New
Jersey. It was also used on the Upper Truckee River near South Lake Tahoe along with a
few other treatments and will be discussed in more detail in Volume II. The design, according
to Miller, is based on a dual fabric system modeled after synthetic fabric retaining walls used
by engineers for road embankments and bridge abutments. The generic system is shown in
Figure 31. Two layers of coconut fiber-based fabric provide both structural strength and
resistance to piping of fine material. Piping is that process where internal erosion of soils
occur; that is, water seeps in from above through a porous layer of soil, such as sand lenses,
and erodes that layer from where it enters to where it exits further down slope. The inner
layer is a loose coconut fiber blanket held together by synthetic mesh netting and is used to
trap finds and prevent piping. The outer layer is a strong, woven coir fabric to provide
structural support. Sometimes, the latter fabric is substituted by even stronger, more durable
synthetic materials, that are formed by a matrix of geosynthetic bands. The disadvantage of
the latter materials, however, is that they are not very biodegradable. Of course, vegetation
would mask the materials so they are not visible.
Miller (1992) describes building the lifts of fabric-reinforcement as follows:
"To build the streambanks, we would first lay down a layer of each fabric in the
appropriate location. We'd place fill material, compact it, and wrap the exposed fabric
over the face of the fill. The fabric would be keyed back under the next layer with
wooden stakes. We'd progress upwards from layer to layer, whether the slopes were
vertical or at a 3:1 slope."
B-49
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