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R.H. Charlier and Chr. P. De Meyer
Sea walls are built to prevent the coastline from further regression. A sea-wall
prevents erosion of the land behind ; it does not protect the shore in front of it.
They are most appropriate for boating and fishing ports. Revetments and
bulkheads play the same role. Revetment designates a facing placed on a bank or
bluff or other stone structure (fig. 22, 23, 24). Revetments are similar, for a
sloping coast, to sea walls, while bulkheads are used to prevent backshore
property of sliding into the surf zone, as happened, for instance on Long Island
(NY). Revetments are layers or blankets of strong, non-erodable material placed
on the shore. Stone revetments have been used, for instance, at Johns Pass,
Treasure Island (Florida). Revetments built on relatively gentle slopes are stable ;
they do not greatly interfere with littoral drift. Nevertheless they may induce local
erosion elsewhere ; this is particularly true if they are steep. While themselves
either porous or watertight, they are subject to scour at their toe where a rock
apron is best placed (fig. 25).
In the Netherlands, paved stones have been traditionally used as revetments
although asphalt revetments are not unusual. Studies were recently carded out
dealing with the relationships between external wind-wave pressures and
pressure gradients underneath the stones in sublayers of granular material. This
allows making a quantitative check of the revetment stability.
Asphalt may well become the more common material not only because of a
progressive shortage of paved stones but because it permits to complete work in a
shorter span of time. Asphalt concrete on sand is an approach that is followed on
a large scale along Dutch shores. Sea-walls and bulkheads must be high enough
to prevent overtopping, have a toe protected against scour, weep holes to relieve
pressure, be securely anchored and tied so as not to tip and defended against
percolation and run-off (fig. 25).
Bulkheads resist substantial wave forces by transmitting impact loads into the soil
behind the wall, but waves can rapidly destroy a bulkhead if the backfill is lost.
Unlike the bulkhead, a free standing wooden breakwater must rely on the
strength of its materials to resist wave impacts. Traditional wooden breakwaters
used for marina or harbor protection are designed as a total wave barrier with
minimal overtopping. To survive waves, they must be heavily constructed and
much more expensive than a bulkhead with a similar exposure.
R.H. Charlier and Chr. P. De Meyer
Sea walls are built to prevent the coastline from further regression. A sea-wall
prevents erosion of the land behind ; it does not protect the shore in front of it.
They are most appropriate for boating and fishing ports. Revetments and
bulkheads play the same role. Revetment designates a facing placed on a bank or
bluff or other stone structure (fig. 22, 23, 24). Revetments are similar, for a
sloping coast, to sea walls, while bulkheads are used to prevent backshore
property of sliding into the surf zone, as happened, for instance on Long Island
(NY). Revetments are layers or blankets of strong, non-erodable material placed
on the shore. Stone revetments have been used, for instance, at Johns Pass,
Treasure Island (Florida). Revetments built on relatively gentle slopes are stable ;
they do not greatly interfere with littoral drift. Nevertheless they may induce local
erosion elsewhere ; this is particularly true if they are steep. While themselves
either porous or watertight, they are subject to scour at their toe where a rock
apron is best placed (fig. 25).
In the Netherlands, paved stones have been traditionally used as revetments
although asphalt revetments are not unusual. Studies were recently carded out
dealing with the relationships between external wind-wave pressures and
pressure gradients underneath the stones in sublayers of granular material. This
allows making a quantitative check of the revetment stability.
Asphalt may well become the more common material not only because of a
progressive shortage of paved stones but because it permits to complete work in a
shorter span of time. Asphalt concrete on sand is an approach that is followed on
a large scale along Dutch shores. Sea-walls and bulkheads must be high enough
to prevent overtopping, have a toe protected against scour, weep holes to relieve
pressure, be securely anchored and tied so as not to tip and defended against
percolation and run-off (fig. 25).
Bulkheads resist substantial wave forces by transmitting impact loads into the soil
behind the wall, but waves can rapidly destroy a bulkhead if the backfill is lost.
Unlike the bulkhead, a free standing wooden breakwater must rely on the
strength of its materials to resist wave impacts. Traditional wooden breakwaters
used for marina or harbor protection are designed as a total wave barrier with
minimal overtopping. To survive waves, they must be heavily constructed and
much more expensive than a bulkhead with a similar exposure.