220
R.H. Charlier and Chr. P. De Meyer
It has been suggested (J. De Rouck, op. cit.) to use HARO blocks, mentioned
earlier, instead of tetrapods, a.o. reasons because the quantity of concrete is then
reduced by approximately one fourth. This armoring element has a considerably
greater hydraulic stability than cubes and tetrapods, roughly the same as an
accropode (Anonymous, 1990, Accropode : The ideal block for efficient and
economic protection of breakwaters : Grenoble, Soc. Gren. A. Hydr.
SOGREAH), and has in many case a performance better than or equal to dolos.
Quadripods have been used as armor to reinforce breakwaters. The tetrapod is an
unreinforced nonblock concrete unit with four truncated conical legs projecting
radially from a center. Quadripods are a U.S. newer development of the French
product. The tribar is an assembly of three cylinders connected by three radial
arms. A dolo resembles a ship anchor ; its straight flukes shaped central shank
ends are replaced by triangular heads in a toskane. Modified cubes and hexapods
have also been tested. It should be recalled here that concrete armor units have
breakage problems which are not encountered with quarrystone.
The above listing of units is not comprehensive : about 40 types are in existence
(cf. Hudson, R.Y., 1974, Concrete armor units for protection against wave
attack. Report of the ad hoc Committee on Artificial Armor Units for Coastal
Structures : Vicksburg MS, U.S. Army Engineers Waterways Experiment Station
(Document H-74-2)). They were developed in ten different countries, principally
the United States, Great Britain, Japan and The Netherlands.
2.1.9
Others
Several other methods and designs have been proposed ; some are proprietary.
Beach nourishment (cf. section 3) and vegetation are among the most effective.
Timber cribs filled with brush constitute breakwaters that can allow vegetation to
become established. Vegetation stabilizes dunes and protects marshes, enhancing
simultaneously the environmental aesthetic attractiveness. Its roots and stems
traps fine sand and soil, and in marshes absorb some wave and current energy.
Types of plants must be carefully selected, and since they are usually less
resistant than the natives ones, sand fences should be used during their
colonisation period of the area.
Low retaining sills can also trap sand. Being submerged, they have no
unaesthetic effect. They create a beach at a height higher than the original level ;
such perched beaches are generally built where nourishment at the original level
would be very costly due to rapid removal of fill material. They do offer some
shore protection. Materials and designs are similar to those of breakwaters but
must be of interlocking tongue-and-groove elements or have filter material. The
beach itself can be artificially nourished (cf. 3) or be built from inshore wave
carded sand but then with risk of depletion on adjoining beaches.
R.H. Charlier and Chr. P. De Meyer
It has been suggested (J. De Rouck, op. cit.) to use HARO blocks, mentioned
earlier, instead of tetrapods, a.o. reasons because the quantity of concrete is then
reduced by approximately one fourth. This armoring element has a considerably
greater hydraulic stability than cubes and tetrapods, roughly the same as an
accropode (Anonymous, 1990, Accropode : The ideal block for efficient and
economic protection of breakwaters : Grenoble, Soc. Gren. A. Hydr.
SOGREAH), and has in many case a performance better than or equal to dolos.
Quadripods have been used as armor to reinforce breakwaters. The tetrapod is an
unreinforced nonblock concrete unit with four truncated conical legs projecting
radially from a center. Quadripods are a U.S. newer development of the French
product. The tribar is an assembly of three cylinders connected by three radial
arms. A dolo resembles a ship anchor ; its straight flukes shaped central shank
ends are replaced by triangular heads in a toskane. Modified cubes and hexapods
have also been tested. It should be recalled here that concrete armor units have
breakage problems which are not encountered with quarrystone.
The above listing of units is not comprehensive : about 40 types are in existence
(cf. Hudson, R.Y., 1974, Concrete armor units for protection against wave
attack. Report of the ad hoc Committee on Artificial Armor Units for Coastal
Structures : Vicksburg MS, U.S. Army Engineers Waterways Experiment Station
(Document H-74-2)). They were developed in ten different countries, principally
the United States, Great Britain, Japan and The Netherlands.
2.1.9
Others
Several other methods and designs have been proposed ; some are proprietary.
Beach nourishment (cf. section 3) and vegetation are among the most effective.
Timber cribs filled with brush constitute breakwaters that can allow vegetation to
become established. Vegetation stabilizes dunes and protects marshes, enhancing
simultaneously the environmental aesthetic attractiveness. Its roots and stems
traps fine sand and soil, and in marshes absorb some wave and current energy.
Types of plants must be carefully selected, and since they are usually less
resistant than the natives ones, sand fences should be used during their
colonisation period of the area.
Low retaining sills can also trap sand. Being submerged, they have no
unaesthetic effect. They create a beach at a height higher than the original level ;
such perched beaches are generally built where nourishment at the original level
would be very costly due to rapid removal of fill material. They do offer some
shore protection. Materials and designs are similar to those of breakwaters but
must be of interlocking tongue-and-groove elements or have filter material. The
beach itself can be artificially nourished (cf. 3) or be built from inshore wave
carded sand but then with risk of depletion on adjoining beaches.