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 Surface Armor for Erosion Protection
stone to be placed, without creating a hazardous condition for construction personnel in the
interim.
Environmental or land use considerations may limit the area available for the disposal
of material excavated from the trench. Within those limitations, excavated material can be
placed either riverward or landward of the trench. If it is placed riverward of the trench, it
will be eroded away as the river channel migrates toward the revetment, although it should
be placed so that it does not cause geotechnical bank failures that might affect the integrity
of the stone in the trench before it launches. If it is placed landward of the trench, the
geotechnical design of the work should account for its presence, and proper routing of surface
drainage should be provided for. Unless it is certain that natural revegetation will occur on
the disposal area within a short time after completion of construction, vegetation should be
established as part of the construction operation. Since the disposal area will be built up
higher than the adjacent ground, habitat diversity can be improved by establishing species of
vegetation that are less tolerant of flooding than the existing species.
A portion of the excavated material can be placed so that it becomes an extension of
the bank slope, in order to provide a greater degree of control over the direction of flows at
river stages which would otherwise overtop the natural bank. This is more likely to be
desirable in cases where the channel alongside the revetment will be used by navigation traffic
than in cases where prevention of channel migration is the only project purpose. In such
cases, the material should be semi-compacted as it is placed, and then protected from erosion
as if it were part of the original bank.
7.1.3 WINDROW
7.1.3.1 Description
A windrow revetment is simply an extreme variation of a trenchfill revetment. A
windrow revetment consists of rock placed on the floodplain surface landward from the
existing bankline at a pre-determined location, beyond which additional erosion is to be
prevented as shown in Figures 7.3 through 7.6.
7.1.3.2 Advantages
A windrow has the same advantages as a trenchfill, and is even simpler to design and
construct.
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