Figure 6.30. Permissible velocities of various protection materials as
a function of flow duration (Hewlett et al. 1987).
Notes to Figure:
Minimum superficial mass 135 kg/m (28 lb/ft )
Minimum nominal thickness 20 mm (0.8 inch)
Installed within 20 mm (0.8 inch) of soil surface, or in conjunction with a surface mesh
These graphs should only be used for erosion resistance to unidirectional flow. Values
are based on available experience and information at the date of this report.
5. All reinforced grass values assume well established, good grass cover.
6. Other criteria (such as short-term protection, ease of installation and management,
susceptibility to vandalism) must be considered in choice of reinforcement.
6.8.5 Overtopping Protection Systems
A number of material types and manufactured systems have been identified for use in
minimizing or preventing erosion of embankments subjected to overtopping flow. Listed
below are protection systems which have been the subject of various investigation over the
last several decades. These systems are described in detail in a summary report issued by
the ASCE Task Committee on Overtopping Protection (Oswalt et al. 1994):
Roller Compacted Concrete
Cast in Place Concrete
Articulating Concrete Blocks