216
R.H. Charlier and Chr. P. De Meyer
Design and construction of artificial seaweeds varies depending upon the
projected use : either for an artificial reef for anti-erosion coastal protection, or to
reduce scouring of footings of at-sea structures and pipelines. Conclusions
reached by workers at Scripps Institution of Oceanography (California) are that at
fundamental frequency the reef has no significant effect on wave energy, though
it absorbs significantly such energy at higher harmonies. Besides inadequate
anchoring units are fast buried by scouring action when mass transport is
important, and when they can resist it, they suffer from scour around the anchor,
bury themselves into the sand and cause no accretion. Observed beach profile
changes were not due to reef implantation.
The Nicolon gas injected polypropylene weed was used as early as 1973 to
counter scour in The Netherlands. In 5 out of II sites positive results were
registered. Experiments were conducted around drilling platforms ; claims of
reduced scour were made.
Erosion reduction experiments were already tried in 1963 in the Danish North
Sea Coast, followed by others in the United States (Ocean City NJ, Wallops
Island VA), Great Britain and France (Saintes Marie de la Mer) ; all failed due to
anchoring problems. In France, an apparent success in calmer waters was
eventually disputed and considered anti-scour action. Of the numerous later tests
two were hailed as successes but challenged afterwards : at Cape Hatteras SC the
results were attributed to shoreline modification and at Long Beach CA profiling
showed erosion over the reef.
Significant changes in elongation, strength weight and flotation showed among
seven to thirteen month old samples. Seascape completely failed within eight to
20 months of installation, depending on the type of wave energy, environment
and local water quality conditions. If it at first appears cost effective, annual
replacement costs render the technology a cost-ineffective solution to erosion in
Barbados. Seascape (R) Synthetic Seaweed (SSS) has been promoted in the
United States since 1981 as a measure of controlling shoreline erosion. Made of
spun bound polypropylene, the units consist of a weighting anchor tube, a mass of
vertically floating fronds to capture sand, and foam attachments to improve
buoyancy of fronds and to facilitate recovery after flexing. Fronds reduce current
flow so as to allow sand to drop from the water column to form an offshore sand
bar which reduces wave energy and prevents loss of sand to the offshore.
Therefore sand must be available, stirred up, and in suspension.
Reports by Hall, Leadon, Spencer and others concluded from projects conducted
up to 1985 that, neither inside or outside seaweed "sheltered" areas, is there any
meaningful beach profile modification and state that there is "not a single
documented case where artificial seaweed has been successful in controlling
shoreline erosion."
R.H. Charlier and Chr. P. De Meyer
Design and construction of artificial seaweeds varies depending upon the
projected use : either for an artificial reef for anti-erosion coastal protection, or to
reduce scouring of footings of at-sea structures and pipelines. Conclusions
reached by workers at Scripps Institution of Oceanography (California) are that at
fundamental frequency the reef has no significant effect on wave energy, though
it absorbs significantly such energy at higher harmonies. Besides inadequate
anchoring units are fast buried by scouring action when mass transport is
important, and when they can resist it, they suffer from scour around the anchor,
bury themselves into the sand and cause no accretion. Observed beach profile
changes were not due to reef implantation.
The Nicolon gas injected polypropylene weed was used as early as 1973 to
counter scour in The Netherlands. In 5 out of II sites positive results were
registered. Experiments were conducted around drilling platforms ; claims of
reduced scour were made.
Erosion reduction experiments were already tried in 1963 in the Danish North
Sea Coast, followed by others in the United States (Ocean City NJ, Wallops
Island VA), Great Britain and France (Saintes Marie de la Mer) ; all failed due to
anchoring problems. In France, an apparent success in calmer waters was
eventually disputed and considered anti-scour action. Of the numerous later tests
two were hailed as successes but challenged afterwards : at Cape Hatteras SC the
results were attributed to shoreline modification and at Long Beach CA profiling
showed erosion over the reef.
Significant changes in elongation, strength weight and flotation showed among
seven to thirteen month old samples. Seascape completely failed within eight to
20 months of installation, depending on the type of wave energy, environment
and local water quality conditions. If it at first appears cost effective, annual
replacement costs render the technology a cost-ineffective solution to erosion in
Barbados. Seascape (R) Synthetic Seaweed (SSS) has been promoted in the
United States since 1981 as a measure of controlling shoreline erosion. Made of
spun bound polypropylene, the units consist of a weighting anchor tube, a mass of
vertically floating fronds to capture sand, and foam attachments to improve
buoyancy of fronds and to facilitate recovery after flexing. Fronds reduce current
flow so as to allow sand to drop from the water column to form an offshore sand
bar which reduces wave energy and prevents loss of sand to the offshore.
Therefore sand must be available, stirred up, and in suspension.
Reports by Hall, Leadon, Spencer and others concluded from projects conducted
up to 1985 that, neither inside or outside seaweed "sheltered" areas, is there any
meaningful beach profile modification and state that there is "not a single
documented case where artificial seaweed has been successful in controlling
shoreline erosion."