IV. R~reating Shorelines
255
Basically, there are two main features which influence the possibilities available
for the execution method : the distance between the borrow area and the
reclamation site, and the requirement for nearshore dumping or beach
replenishment. The former determines whether direct pumping from the borrow
area to the reclamation site is feasible, while the latter determines whether direct
pumping with hopper dredgers or barges is needed.
When fill material is required in the nearshore zone but, due to wave conditions,
it is not feasible to dump in this zone with hopper dredgers or barges, a rainbowsystem can be used which entails jetting the sand-water mixture under
approximately 45 ° from a hopper dredger or from a stationary dredger (equipped
if necessary with a flexible floating pipeline and a moored nozzle barge).
Distances up to 75 m (274 t) can be reached. However, it is difficult to control
the dumping process.
3.1.7. 4.1 Direct dumping in the nearshore zone
Or.
Conditions
Very good sea and weather conditions are required. The final level depends
upon the draught (draft) of the loaded vessels which have to enter the area
to dump their load.
Equipment and execution :
This method can be performed by trailing suction hopper dredgers capable
of shallow dumping. Hopper capacity of the vessels is limited and systems
may not have protruding bottom doors such as sliding bottom doors or split
hull hopper dredgers.
Dumping by barges loaded by a stationary suction dredger is also a solution
if sea conditions make it possible. Seaworthy barges, however, will always
be required. By using barges, the minimum required water depth can be
decreased.
Monitoring is needed. Survey and dumping vessels should be equipped with
radio positioning systems.
3.1.7.4.2 Direct pumping to the beach area
The methods proposed depend upon the location of the borrow area.
Or.
When the borrow area is at sea, trailing suction hopper dredgers should be
used. The vessel loads at sea, sails to a mooring point as near as possible to
the beach area and pumps its load ashore.
255
Basically, there are two main features which influence the possibilities available
for the execution method : the distance between the borrow area and the
reclamation site, and the requirement for nearshore dumping or beach
replenishment. The former determines whether direct pumping from the borrow
area to the reclamation site is feasible, while the latter determines whether direct
pumping with hopper dredgers or barges is needed.
When fill material is required in the nearshore zone but, due to wave conditions,
it is not feasible to dump in this zone with hopper dredgers or barges, a rainbowsystem can be used which entails jetting the sand-water mixture under
approximately 45 ° from a hopper dredger or from a stationary dredger (equipped
if necessary with a flexible floating pipeline and a moored nozzle barge).
Distances up to 75 m (274 t) can be reached. However, it is difficult to control
the dumping process.
3.1.7. 4.1 Direct dumping in the nearshore zone
Or.
Conditions
Very good sea and weather conditions are required. The final level depends
upon the draught (draft) of the loaded vessels which have to enter the area
to dump their load.
Equipment and execution :
This method can be performed by trailing suction hopper dredgers capable
of shallow dumping. Hopper capacity of the vessels is limited and systems
may not have protruding bottom doors such as sliding bottom doors or split
hull hopper dredgers.
Dumping by barges loaded by a stationary suction dredger is also a solution
if sea conditions make it possible. Seaworthy barges, however, will always
be required. By using barges, the minimum required water depth can be
decreased.
Monitoring is needed. Survey and dumping vessels should be equipped with
radio positioning systems.
3.1.7.4.2 Direct pumping to the beach area
The methods proposed depend upon the location of the borrow area.
Or.
When the borrow area is at sea, trailing suction hopper dredgers should be
used. The vessel loads at sea, sails to a mooring point as near as possible to
the beach area and pumps its load ashore.