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Encyclopedia > Dredge

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For other uses, see Dredge (disambiguation).

Dredging is miscellaneous excavation-type work or operation usually carried out underwater, in shallow sea or fresh water area. Image File history File links Information_icon. ... Shortcut: WP:CU Marking articles for cleanup This page is undergoing a transition to an easier-to-maintain format. ... This Manual of Style has the simple purpose of making things easy to read by following a consistent format — it is a style guide. ... Dredge or dredging may refer to: Dredge, underwater excavation work. ... Excavation is the best-known and most commonly used technique within the science of archaeology. ... For the village on the Isle of Wight, see Freshwater, Isle of Wight. ...


A dredge is a device for scraping or sucking the seabed, used for dredging.


A dredger is a ship or boat equipped with a dredge.


In American usage any floating vessel equipped with dredging equipment is called a dredge.


Types of dredging

  • Capital dredging: carried out to create a new harbor or berth or waterway, or deepen an existing one in order to allow larger ships to use it. It is usually carried out with a cutter-suction dredge.
  • Maintenance dredging: deepening navigable waterways which have become silted with the passage of time, due to sand and mud deposited by water currents, until they may become too shallow for navigation. This is often carried out with a trailing suction hopper dredge. Most dredging is for this purpose.
  • Land reclamation: mining sand, clay or rock from the seabed and using it to construct new land. This is typically performed by a cutter-suction dredge or trailing suction hopper dredge.
  • Beach Nourishment: mining sand offshore and placing on a beach to replace sand eroded by storms or wave action. This is done to enhance the recreational and protective function of the beaches. This is typically performed by a cutter-suction dredge or trailing suction hopper dredge.
  • Removing trash and debris from the bottoms of rivers and canals and harbors.
  • Getting useful material from the seabed. One possible type in the future, is recovering natural metal ore nodules from the abyssal plains.
  • Contaminant remediation. Dredging is often used to reclimate areas affected by chemical spills, storm water surges (with urban runoff), and other soil contaminations. Disposal becomes an aproportionatly large factor in these operations.
  • Anti-eutrophication. Dredging is an (expensive) option for the remediation of eutrophied (or de-oxygenated) water bodies. As artificialy elevated phosphorus levels in the sediment aggrivate the eutrophication process, controlled sediment removal is occasionally the only option for the reclimation of still waters.

A harbor or harbour (see spelling differences), or haven, is a place where ships may shelter from the weather or are stored. ... Land reclamation is either of two distinct practices. ... Iron ore (Banded iron formation) Manganese ore Lead ore Gold ore An ore is a volume of rock containing components or minerals in a mode of occurrence which renders it valuable for mining. ... Abyssal plains are flat or very gently sloping areas of the deep ocean basin floor. ... Eutrophication is apparent as increased turbidity in the northern part of the Caspian Sea, imaged from orbit. ...

Suction dredgers

These operate by sucking through a long tube, like some vacuum cleaners. A plain suction dredger has no tool at the end of the suction pipe to disturb the material. Regular vacuum cleaner for home use. ...


Trailing suction hopper dredger

A trailing suction hopper dredger or TSHD trails its suction pipe when working, and loads the dredge spoil into one or more hoppers in the vessel. When the hoppers are full the TSHD sails to a disposal area and either dumps the material through doors in the hull or pumps the material out of the hoppers.


Cutter-suction dredger

In a cutter-suction dredger or CSD, the suction tube has a cutter head at the suction inlet, to loosen the earth and transport it to the suction mouth. The cutter can also be used for hard surface materials like gravel or rock. The dredged soil is usually sucked up by a wear resistant centrifugal pump and discharged through a pipe line or to a barge. In recent years dredgers with more powerful cutters have been built in order to excavate harder and harder rock without blasting. The two largest cutter suction dredgers in the world are Deme's D'Artagnan (28,200 kW total installed power), and Jan De Nul's J.F.J. DeNul (27,240 kW).


Auger suction dredger

This works like a cutter suction dredger, but the cutting tool is a rotating Archimedean screw set at right angles to the suction pipe. Archimedess screw (also the Archimedean screw) is one of several inventions and discoveries reputed to have been made by Archimedes. ...


Jet-lift dredger

This uses the Venturi effect of a concentrated high-speed stream of water to pull the nearby water, together with bed material, into a pipe. A Venturi meter is shown in a diagram, the pressure in 1 conditions is higher than 2, and the relationship between the fluid speed in 2 and 1 respectively, is the same as for pressure. ...


Air-lift dredger

An Airlift (dredging device) is a type of small suction dredge. It is sometimes used like other dredges. At other times, often an airlift is used handheld underwater by a diver. It works by blowing air into the pipe, and dragging water with it. An Airlift is device based on a pipe, used in nautical archaeology to suck small objects, sand and mud from the sea bed and to transport the resulting debris upwards and away from its source. ... A diver is an person who practices scuba diving or surface supplied diving. ...


Bucket dredger

A bucket dredger is a dredger equipped with a bucket dredge, which is a device that picks up sediment by mechanical means, often with many buckets attached to a wheel or chain. Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. ... A driving wheel on a steam locomotive. ...


Some bucket dredgers and grab dredgers are powerful enough to rip out coral reef to make a shipping channel. Some of the biodiversity of a coral reef. ...


Grab dredger

A grab dredger picks up seabed material with a clamshell grab, which hangs from an onboard crane, or is carried by a hydraulic arm, or is mounted like on a dragline. This technique is often used in excavation of bay mud. They are also known as 'Priestman Grabs'. Huge Manitowok 4600 Heavy lift Dragline at the SNS Project, 2005. ... Richardson Bay mudflats of are exposed layers of bay mud Bay mud consists of thick deposits of soft, unconsolidated silty clay, which is saturated with water; these soil layers are situated at the bottom of certain estuaries, which are normally in temperate regions that have experienced cyclical glacial cycles. ...


Backhoe/dipper dredge

A backhoe/dipper dredge has a backhoe like on some excavators. A crude but usable backhoe dredger can be made by mounting a land-type backhoe excavator on a pontoon. Picture 1:Backhoe used for work on the street Picture 2:Skid loader with bucket replaced by backhoe attachment A backhoe, also called a rear actor or back actor, is a piece of excavating equipment consisting of a digging bucket on the end of an articulated arm (also called a... A tracked excavator by Daewoo. ... Picture 1:Backhoe used for work on the street Picture 2:Skid loader with bucket replaced by backhoe attachment A backhoe, also called a rear actor or back actor, is a piece of excavating equipment consisting of a digging bucket on the end of an articulated arm (also called a... A tracked excavator by Daewoo. ... A pontoon boat, like this small pleasure boat, typically floats and balances by means of two pontoons oriented in the direction of travel. ...


The two largest backhoe dredgers in the world are Tauracavor and New York. Both feature a barge mounted excavator.


Water injection dredger

A water injection dredger injects water in a small jet under low pressure (low pressure because the sediment should not explode into the surrounding waters, rather it is carefully moved to another location) into the seabed to bring the sediment in suspension, which then becomes a turbidity current, which flows away downslope, is moved by a second burst of water from the WID or is carried away in natural currents. Opposition claims that Water Injection Dredging is not a natural way of dredging while the side of the WID claims otherwise. As a side note: Water injection results in a lot of sediment in the water which makes measurement with most hydrographic equipment (for instance: singlebeam echosounder) difficult and should make use of filtering to produce better results. A turbidity current or density current is a current of of rapidly moving, sediment-laden water moving down a slope through air, water, or another fluid. ...


Pneumatic dredger

Here, there is a chamber with inlets. The water is pumped out of it with the inlets closed. The inlets are then opened to let material in. The chamber is then pumped empty. The cycle is repeated. It is usually suspended from a crane on land or from a small pontoon or barge. Its effectiveness depends on depth pressure.


Bed leveler

This is a bar or blade which is pulled over the seabed behind any suitable ship or boat. It has the effect of a bulldozer. A Caterpillar D10N bulldozer at work A bulldozer is a very powerful crawler (caterpillar tracked tractor) equipped with a blade. ...


Krabbelaar

This is an early type of dredger which was formerly used in shallow water in the Netherlands. It was a flat-bottomed boat with spikes sticking out of its bottom. As tide current pulled the boat, the spikes scraped seabed material loose, and the tide current washed the material away, hopefully to deeper water. Krabbelaar is Dutch for "scratcher".


Fishing dredges

There are types of dredges used for collecting scallops or oysters from the seabed. They tend to have the form of a scoop made of chain mesh. They are towed by a fishing boat. Scallop dredging is very destructive to the seabed, and nowadays is often replaced by scuba diving to collect the scallops. Genera See text. ... Crassostrea gigas, Marennes-Oléron Crassostrea gigas, Marennes-Oléron Crassostrea gigas, Marennes-Oléron, opened The name oyster is used for a number of different groups of mollusks which grow for the most part in marine or brackish water. ... A fishing boat can range from two-person pleasure fishing boats up to 7-8 ton commercial fishers that can haul in over a billion fish at one time. ... Scuba divers exploring fish and coral. ...


Amphibious dredger

Some of these are any of the above types of dredger, which can operate normally, or by extending legs so it stands on the seabed with its hull out of the water. Some forms can go on land.


Some of these are land-type backhoe excavators whose wheels are on long hinged legs so it can drive into shallow water and keep its cab out of water. Some of these may not have a floatable hull and, if so, cannot work in deep water. Picture 1:Backhoe used for work on the street Picture 2:Skid loader with bucket replaced by backhoe attachment A backhoe, also called a rear actor or back actor, is a piece of excavating equipment consisting of a digging bucket on the end of an articulated arm (also called a... A tracked excavator by Daewoo. ...

  • Oliver Evans (1755-1819) in 1804 invented an amphibious dredger which was America's first steam-powered road vehicle.

Oliver Evans Oliver Evans (13 September 1755 – 15 April 1819) was a United States inventor. ... Oliver Evans Oliver Evans (13 September 1755 – 15 April 1819) was a United States inventor. ...

Submersible dredger

These are usually used to recover useful materials from the seabed. Many of them travel on caterpillar tracks. Caterpillar tracks are large (modular) tracks used on tanks, construction equipment and certain other off-road vehicles. ...


This link describes a type intended to walk on legs on the seabed. It is a summary of the article "Concept of a mathematical model for prediction of major design parameters of a submersible dredger/miner" by Sritama Sarkar, Neil Bose, Mridul Sarkar, and Dan Walker, in "3rd Indian National Conference on Harbour and Ocean Engineering, National Institute of Oceanography", Dona Paula, Goa 403 004 India, 7 - 9 December 2004: see http://www.nio.org for more information about publisher etc. For other uses, see Goa (disambiguation). ... A publisher is a person or entity which engages in the act of publishing. ...


Drag

In some police departments a small dredge (sometimes called a drag) is used to find and recover objects and bodies from underwater. The bodies may be murder victims, or people who committed suicide by drowning, or victims of accidents. It is sometimes pulled by men walking on the bank. Suicide (from Latin sui caedere, to kill oneself) is the act of willfully ending ones own life. ...


Disposal of the dredgings

In a "hopper dredger", the dredgings end up in a big onboard hold called a "hopper", which has doors in its bottom. The excess water in the dredgings is spilled off by sedimentation: as the mud and sand settle to the bottom of the hopper, the water is siphoned from the top and returned to the sea to reduce weight and increase the amount of dredgings that can be carried in one load. When the hopper is filled with slurry, the dredger stops dredging and goes to a dump site and opens the bottom hopper doors, dumping the slurry out. Or the hopper can be emptied from above. A suction hopper dredger is usually used for maintenance dredging. A slurry is a mixture, which comes in different varieties: Metal Slurry can be used in pipe fitting and other welding tasks, as well as slurry based bombs like the BLU-82. ...


Sometimes with a suction dredger the slurry of dredgings and water is pumped straight into pipes which deposit it on nearby land by pipes; or in barges (also called scows), which deposit it in the deep sea or on land. Self propelled barge carrying bulk crushed stone A barge is a flat-bottomed boat, built mainly for river and canal transport of heavy goods. ... A scow, in the original sense, is a flat bottomed boat with a blunt bow, often used to haul garbage or similar bulk freight; cf. ...


When contaminated (toxic) sediments are removed, or large volume inland disposal sites are unavailable, dredge sluries are reduced to dry solids via a process known as dewatering. Current dewatering techniques employ either centrifuges, large textile based filters or polymer flocculant / congealant based apparatus.


In many projects, slurry dewatering is performed in large inland settling pits, although this is becoming less and less proliferant as mechanical dewatering techniques continue to improve.


Similarly, many groups (most notable in east Asia) are performing research towards utilizing dewatered sediments for the production of concretes and construction block, although the high organic content (in many cases) of this material is a hindrance toward such ends.


History

WT Preston, a museum ship formerly a specialized river dredge, also called a "snagboat." The W.T. Preston is a specialized paddle steamer that operated as a river dredger, otherwise known as a snagboat, removing log jams and natural debris that prevented river navigation on several Puget Sound-area rivers, including the Skagit, Stillaguamish, and Snohomish rivers. ...


Images

See also

Wikimedia Commons has media related to:
Dredge ships

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