DREDGING
Dredging is the process by which sediments and debris are removed from the bottom of shipping
channels, rivers, harbors, and other water bodies
It is a technique, often used to keep waterways navigable and creates an anti-sludge pathway for boats.
It is also used as a way to replenish sand on some public beaches, where sand has been lost because of
coastal erosion.
Dredger is an apparatus for bringing up objects, sand or mud from a river or a seabed by scooping &
dragging.
Factors that affect dredge production
• Material characteristic
• Discharge pipe length
• Termination elevation
• Digging depth
• Dredge pump location on the dredge
Material characteristics
Dredge performance Is a function of the slurry specific gravity. The higher the specific gravity, the higher
the production.
Discharge pipe length
As a dredger moves farther away from the discharge point, the pump speed is increased to maintain a
proper slurry velocity within the pipeline. Once maximum pump speed has been achieved, further
increasing the discharge distance causes the cost per ton of material move to rise while production
declines
Digging depth
At deeper depths it takes more energy to overcome two things, lifting of material from the deeper
depth up to the pump and increased friction due to a longer suction pipe. The negative impact of
production is minimal when suction head loss is less than 9m
Dredging pump location on the dredge
A dredge with a hull mounted pump will produce less material as the digging depth increases.
The available energy/pressure for a hull pump is only one atmosphere. for a submerged pump the
available energy /pressure is one atmosphere plus the pressure provided by depth of water above the
pump inlet.
Other factors that may affect dredge production include atmospheric pressure, design and condition of dredge and
supporting equipment, skill of management and operation staff.
Uses of dredgers
1) Capital: Dredging is carried out to create a new harbor, berth or waterway, or to deepen existing
facilities in order to allow larger ships access. This work is usually done by using a cutter suction dredge
or large trailing suction hopper dredge.
Dredging Kiprotich 2021©
, 2) Preparatory: This excavation work is prepared for future bridges, piers or docks/wharves, often
connected with foundation work.
3) Maintenance: Dredging maintain navigable waterways or channels which becomes silted with the
passage of time, due to sedimented sand and mud, makes them too shallow for navigation. This is often
carried out with a trailing suction hopper dredge. Mostly dredging is used for this purpose.
4) Land Reclamation: Dredging to mine sand, clay or rock from the seabed and using it to construct new
land elsewhere. This is performed by a cutter- suction dredge or trailing suction hopper dredge.
5) Harvesting materials: Dredging sediment for elements like gold, diamonds or other valuable trace
substances.
6) Seabed mining: It can be used probably in future for recovering natural metal ore nodules from the
sea abyssal’s plains.
7) Construction materials: Dredging sand and gravels from offshore licensed regions can be used in
construction industry, principally for use in concrete.
8) Beach Nourishment: Mining sand offshore and placing on a beach, is used to replace sand eroded by
storms or wave action. This is done to enhance the protective function of the beaches.
9) Flood Prevention: This can help to increase channel depth and therefore increase a channel's
capacity for carrying water.
10) Contaminant Remediation: To reclaim the areas affected by chemical spills, storm water surges
(with urban runoff) and other soil contaminations, including silt from sewage sludge and from decayed
matter, like wilted plants. Disposal becomes a proportionally large factor in these operations.
USES OF DREDGING
Dredging, is used for a number of purposes such as:
Waterway Maintenance: Dredging is an important waterway maintenance step, which is probably its
most important application. By removing the accumulated debris, dredging can restore the waterway to
its original depth and condition. Dredging also removes dead vegetation, pollutants, and trash that have
gathered in these areas.
Create waterways: Many ports are building new waterways with dredging to reach new trade centers
and improve the efficiency of the transport of goods. Dredging ensures cargo vessels of all sizes can dock
and do not run aground.
Excavation: Sediment removal plays an important role in the preparation for construction projects such
as bridges, docks and piers by performing the necessary underwater excavation work.
Dredging Kiprotich 2021©
Dredging is the process by which sediments and debris are removed from the bottom of shipping
channels, rivers, harbors, and other water bodies
It is a technique, often used to keep waterways navigable and creates an anti-sludge pathway for boats.
It is also used as a way to replenish sand on some public beaches, where sand has been lost because of
coastal erosion.
Dredger is an apparatus for bringing up objects, sand or mud from a river or a seabed by scooping &
dragging.
Factors that affect dredge production
• Material characteristic
• Discharge pipe length
• Termination elevation
• Digging depth
• Dredge pump location on the dredge
Material characteristics
Dredge performance Is a function of the slurry specific gravity. The higher the specific gravity, the higher
the production.
Discharge pipe length
As a dredger moves farther away from the discharge point, the pump speed is increased to maintain a
proper slurry velocity within the pipeline. Once maximum pump speed has been achieved, further
increasing the discharge distance causes the cost per ton of material move to rise while production
declines
Digging depth
At deeper depths it takes more energy to overcome two things, lifting of material from the deeper
depth up to the pump and increased friction due to a longer suction pipe. The negative impact of
production is minimal when suction head loss is less than 9m
Dredging pump location on the dredge
A dredge with a hull mounted pump will produce less material as the digging depth increases.
The available energy/pressure for a hull pump is only one atmosphere. for a submerged pump the
available energy /pressure is one atmosphere plus the pressure provided by depth of water above the
pump inlet.
Other factors that may affect dredge production include atmospheric pressure, design and condition of dredge and
supporting equipment, skill of management and operation staff.
Uses of dredgers
1) Capital: Dredging is carried out to create a new harbor, berth or waterway, or to deepen existing
facilities in order to allow larger ships access. This work is usually done by using a cutter suction dredge
or large trailing suction hopper dredge.
Dredging Kiprotich 2021©
, 2) Preparatory: This excavation work is prepared for future bridges, piers or docks/wharves, often
connected with foundation work.
3) Maintenance: Dredging maintain navigable waterways or channels which becomes silted with the
passage of time, due to sedimented sand and mud, makes them too shallow for navigation. This is often
carried out with a trailing suction hopper dredge. Mostly dredging is used for this purpose.
4) Land Reclamation: Dredging to mine sand, clay or rock from the seabed and using it to construct new
land elsewhere. This is performed by a cutter- suction dredge or trailing suction hopper dredge.
5) Harvesting materials: Dredging sediment for elements like gold, diamonds or other valuable trace
substances.
6) Seabed mining: It can be used probably in future for recovering natural metal ore nodules from the
sea abyssal’s plains.
7) Construction materials: Dredging sand and gravels from offshore licensed regions can be used in
construction industry, principally for use in concrete.
8) Beach Nourishment: Mining sand offshore and placing on a beach, is used to replace sand eroded by
storms or wave action. This is done to enhance the protective function of the beaches.
9) Flood Prevention: This can help to increase channel depth and therefore increase a channel's
capacity for carrying water.
10) Contaminant Remediation: To reclaim the areas affected by chemical spills, storm water surges
(with urban runoff) and other soil contaminations, including silt from sewage sludge and from decayed
matter, like wilted plants. Disposal becomes a proportionally large factor in these operations.
USES OF DREDGING
Dredging, is used for a number of purposes such as:
Waterway Maintenance: Dredging is an important waterway maintenance step, which is probably its
most important application. By removing the accumulated debris, dredging can restore the waterway to
its original depth and condition. Dredging also removes dead vegetation, pollutants, and trash that have
gathered in these areas.
Create waterways: Many ports are building new waterways with dredging to reach new trade centers
and improve the efficiency of the transport of goods. Dredging ensures cargo vessels of all sizes can dock
and do not run aground.
Excavation: Sediment removal plays an important role in the preparation for construction projects such
as bridges, docks and piers by performing the necessary underwater excavation work.
Dredging Kiprotich 2021©
