Surface Armor for Erosion Protection
Channel Stabilization Works stated in 1965 that "Stone is the most commonly
used material for upper bank paving for revetment works, and in most cases
has proved superior to other materials because of durability and ability to
conform to minor irregularities in the slope" (ASCE, 1965). Since that time,
further development and application of manufactured proprietary armor
materials, and increasing emphasis on environmental considerations and the
use of vegetation for erosion control, has tempered that observation to some
degree. However, the favorable attributes of stone armor are not diminished
by the increasing availability of alternative materials. Furthermore, well-
graded stone can often be placed without a separate underlayment material,
because it provides permeability without exposing bank material. This
characteristic may be a crucial factor when comparing the economics of
alternative armor materials.
Disadvantages are: Stone may be more costly than other materials, depending
on its availability. It requires heavy equipment for efficient placement on large
projects. It may be considered unaesthetic for some locations, and may not
compare favorably with other materials in some environmental circumstances.
7.1.1 RIPRAP BLANKET
Detailed discussion of and design guidance for this most common form of stone armor
is provided in Appendix A. Environmental considerations pertinent to the use of riprap armor
are discussed in 5.2.2.
A trenchfill revetment, shown in Figures 7.1 and 7.2, is simply a standard stone armor
revetment with a massive stone toe. It is normally constructed in an excavated trench behind
the river bank, in anticipation that the river will complete the work by eroding to the
revetment, causing the stone toe to launch down and armor the subaqueous bank slope.
Material other than stone, such as broken soil-cement, has been used successfully and
may be less costly than stone, but careful design of the soil/cement mixture, and careful
monitoring of the material mixing, breaking, and placing operation is required.