4. Coastal Erosion and Protection Measures Including Case Studies
117
The other method, i.e., the Dutch Design, discussed by Verhagen [1992]
is widely adopted in many European countries. Based on this method, the
following basic steps should be considered for designing a beach nourishment project.
• Perform Coastal measurements (preferably for a decade).
• Calculate the “loss of sand” in m3/year per Coastal section.
• Add 40% loss.
• Multiply this quantity with a convenient lifetime (say, five years).
• Place this quantity somewhere on the beach between the low-waterminus-l-meter line and the dune foot.
This method is simple and straightforward and does not require mathematical models and wave (or wind) data, but good quality measurements of
the position of the coastline are essential. The above method is based on the
assumption that the beach nourishment has no influence on the long-term
natural behaviour of the coast. Or in other words, the érosion rate before
nourishment equals the érosion rate after nourishment [Verhagen, 1992].
There are four main methods for artificial beach nourishment namely,
offshore Dredging, Direct Placement, Bypass System and trickle Charge.
The offshore dredging method is dredging the sand in the offshore by
a cutter-suction or a trailing suction hopper dredger and placed on the
affected beach that has been experiencing érosion due to storms or wave
action. This method can be accomplished either by Rainbow Pump Method
or pipelines Linked Method. The rainbow method being commonly adopted
in which, a hopper dredge is usually used to dredge and retain it as slurry
as the sand required is to be sprayed onto the required affected area to be
replenished through a nozzle. Since the path of the sprayed slurry resembles
a rainbow it has derived the name. The pipelines linked method is adopted
at locations where the dredgers do not hâve enough draft to dispose the
dredged spoil from the océan. The pipeline is extended from a dredger which
is moored at a certain distance from the shoreline. This type of dredging
System can be used with cutter suction dredgers as well as hopper suction
dredgers. The pipeline can be mounted on a trestle or on a floating barge.
The direct placement method is the transfer of sand the characteristics
of which being quite similar to that at the site to be replenished. This is
achieved by mechanical means through conveyor belts, bulldozers, etc., from
identified sources either from offshore or from land. At locations structures
intercepting the free passage of the littoral drift alongshore, the sand from
117
The other method, i.e., the Dutch Design, discussed by Verhagen [1992]
is widely adopted in many European countries. Based on this method, the
following basic steps should be considered for designing a beach nourishment project.
• Perform Coastal measurements (preferably for a decade).
• Calculate the “loss of sand” in m3/year per Coastal section.
• Add 40% loss.
• Multiply this quantity with a convenient lifetime (say, five years).
• Place this quantity somewhere on the beach between the low-waterminus-l-meter line and the dune foot.
This method is simple and straightforward and does not require mathematical models and wave (or wind) data, but good quality measurements of
the position of the coastline are essential. The above method is based on the
assumption that the beach nourishment has no influence on the long-term
natural behaviour of the coast. Or in other words, the érosion rate before
nourishment equals the érosion rate after nourishment [Verhagen, 1992].
There are four main methods for artificial beach nourishment namely,
offshore Dredging, Direct Placement, Bypass System and trickle Charge.
The offshore dredging method is dredging the sand in the offshore by
a cutter-suction or a trailing suction hopper dredger and placed on the
affected beach that has been experiencing érosion due to storms or wave
action. This method can be accomplished either by Rainbow Pump Method
or pipelines Linked Method. The rainbow method being commonly adopted
in which, a hopper dredge is usually used to dredge and retain it as slurry
as the sand required is to be sprayed onto the required affected area to be
replenished through a nozzle. Since the path of the sprayed slurry resembles
a rainbow it has derived the name. The pipelines linked method is adopted
at locations where the dredgers do not hâve enough draft to dispose the
dredged spoil from the océan. The pipeline is extended from a dredger which
is moored at a certain distance from the shoreline. This type of dredging
System can be used with cutter suction dredgers as well as hopper suction
dredgers. The pipeline can be mounted on a trestle or on a floating barge.
The direct placement method is the transfer of sand the characteristics
of which being quite similar to that at the site to be replenished. This is
achieved by mechanical means through conveyor belts, bulldozers, etc., from
identified sources either from offshore or from land. At locations structures
intercepting the free passage of the littoral drift alongshore, the sand from