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Appendix B: Bioengineering for Streambank Erosion Control -- Guidelines
wedge of the stake actually compresses the wire to hold the brush down. Wattling is a cigar-
shaped bundle of live, shrubby material made from species that root very quickly from the
stem, such as willow and some species of dogwood and alder. These bundles are laid over
the basal ends of the brushmattress material that was placed in the ditch and staked. The
procedure of making wattling bundles and installing them over the brushmattress material is
presented in more detail below (These procedures are modified after Leiser (1994).
Wattling bundles may vary in length, depending on materials available. Bundles taper at
the ends and this is achieved by alternately (randomly) placing each stem so that about one-
half of the basal ends are at each end of the bundle. When compressed firmly and tied, each
bundle is about 15 to 20-cm in diameter in the middle. Bundles should be tied with either
hemp binder twine or can be fastened and compressed by wrapping "pigtails" around the
bundle. Pigtails are commonly used to fasten rebar together. If tied with binder twine, a
minimum of two wraps should be used in combination with a non-slipping knot, such as a
square knot. Tying of bundles should be done on about 38-cm centers. Wattling bundles
should be staked firmly in place with vertical stakes on the downhill side of the wattling not
more than 90 cm on center and with the wedge of the stake pointing upslope. Also, stakes
should be installed through the bundles at about the same distance, but slightly off-set and
turned around so their wedge points downslope. In this way, the wedged stakes, in tandem,
compress the wattling very firmly. Where bundles overlap, an additional pair of stakes should
be used at the midpoint of the overlap. The overlap should be staked with one pair of stakes
through the ends of both bundles while on the inside of the end tie of each bundle. Figures
26 a-b show a schematic of a brushmattress and wattling. Figures 27 a-c show a sequence
of installing a brushmattress with wattling at a workshop. It should be noted that because of
the workshop setting at a mild time of the year, non-dormant vegetative material is being
used. Normally, one would preferably use dormant material.
Both brushmattress and wattling should be covered immediately with soil and tamped.
Soil should be worked into both the brushmattress and wattling by by both tamping and
walking on it. All but the edges of the brushmattress should be covered with soil and about
75 percent of the wattling should be covered leaving some of each exposed to facilitate
sprouting of stems rather than roots.
A brushmattress without any rock toe was used on the North River, Massachusetts, and
performed quite well for two growing seasons until unraveling started to occur, again because
of a lack of toe and upper and lower end protection. This was in a reach where a bankfull
discharge was experienced with an associated average bankfull velocity
B-44

 


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