Surface Armor for Erosion Protection
Longitudinal peaked stone toe protection is easily combined with vegetative treatments for
a composite design (Figure 7.9).
The centerline of the longitudinal peak stone toe protection should be constructed
along a smooth alignment, preferably with a uniform radius of curvature throughout the bend.
The upstream and downstream ends of the structure should be protected against flanking and
Where the bank materials are highly erodible, and the adequacy of an unsupported
stone placed along the toe of the bank may be marginal, stone dikes can be placed at intervals
as "tiebacks" to prevent erosion from forming behind the structure. A spacing of one to two
multiples of channel width can be used between tiebacks. At the very least, a tieback at the
downstream limit of the structure is recommended.
Longitudinal Stone Fill Toe Protection. With longitudinal stone fill toe protection,
a top elevation and crown width for the stone are specified, along with bank grading and/or
filling to provide for a consistent cross-section of stone. The finished product could just as
easily be classified as a thickened stone armor to provide a launchable toe, with the top
elevation of the armor being well below top bank elevation. In fact, this method is sometimes
referred to as reinforced revetment. There are two basic configurations of longitudinal stone
fill toe protection. One method is to place the toefill stone adjacent to the high bank with the
tieback stone fill placed in trenches excavated into the high bank as shown in Figure 7.10. In
some instances it may be necessary to place the toefill stone riverward of the high bank as
shown in Figure 7.11. Longitudinal stone fill toe protection is often used as the toe
protection with other methods for upper bank protection.
Longitudinal stone fill toe protection can be "notched" in the same manner as a
transverse dike or retard in order to provide an aquatic connection between the main channel
and the area between the structure and the bank slope.
7.2 OTHER SELF-ADJUSTING ARMOR
Some armor materials other than stone which have the ability to adjust to scour,
settlement, or surface irregularities are:
Sacks filled with earth, sand, and/or cement; and
Materials which have been occasionally used in the past, but which have serious