Editing Dredging (section)

==Types==
===Suction dredgers===
[[Image:Pogłębiarka „Sawa”, głowica, Wisła, Saska Kępa, Warszawa 3.jpg|thumb|The [[dredge drag head]] of a suction dredge [[barge]] on the [[Vistula River]] in [[Warsaw, Poland]]]]
[[File:Sudging dredger Tuk87-47-10.jpg|thumb|sudging dredger in the [[Beaufort Sea]] used to build artificial islands for oil prospection]]
[[File:2022-10-06 01 Dredger PROVINCIA DE EL ORO NO I, III & IV.jpg|thumb|Cutter-suction dredger, ''Provincia de el Oro No 1'', in Puerto Bolivar, Ecuador]]
[[Image:Geopotes 14.jpg|thumb|The ''Geopotes 14'' lifting its boom on a canal in The Netherlands. (''gēopotēs'' is Greek for "that which drinks earth")]]
[[File:Berky Dredge King Typ 6780.jpg|thumb|alt=Dredge boat 'Dredge-King'|After collecting, the material can be transported to the shore via tube]]
{{For|suction-type excavation out of water|Suction excavator}}
These operate by sucking through a long tube like some [[vacuum cleaner]]s but on a larger scale.

A plain suction dredger has no tool at the end of the suction pipe to disturb the material.

====Trailing suction====
A trailing suction hopper dredger (TSHD) trails its suction pipe when working. The pipe, which is fitted with a [[dredge drag head]], 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. Some dredges also self-offload using drag buckets and conveyors.{{citation needed|date=July 2018}}

{{asof|2008}} the largest trailing suction hopper dredgers in the world were [[Jan De Nul]]'s ''Cristobal Colon'' (launched 4 July 2008<ref>{{cite web|url=http://www.sandandgravel.com/news/article.asp?v1=11114 |title=Jan de Nul's mega trailer Cristóbal Colón launched - Dredging News Online |publisher=Sandandgravel.com |date=7 July 2008 |access-date=14 June 2013}}</ref>) and her sister ship ''Leiv Eriksson'' (launched 4 September 2009<ref>{{cite web|url=http://www.sandandgravel.com/news/article.asp?v1=11221 |title=Keel-laying ceremony for Jan de Nul's Leiv Eiriksson held - Dredging News Online |publisher=Sandandgravel.com |date=1 September 2008 |access-date=14 June 2013}}</ref>). Main design specifications for the ''Cristobal Colon'' and the '' Leiv Eriksson'' are: 46,000&nbsp;cubic metre hopper and a design dredging depth of 155&nbsp;m.<ref>{{cite web|url=http://www.jandenul.com |title=Jan De Nul Group |publisher=Jandenul.com |date=7 June 2013 |access-date=14 June 2013}}</ref> Next largest is ''HAM 318'' ([[Van Oord]]) with its 37,293&nbsp;cubic metre hopper and a maximum dredging depth of 101&nbsp;m.

====Cutter-suction====
A cutter-suction dredger's (CSD) suction tube has a cutting mechanism at the suction inlet. The cutting mechanism loosens the bed material and transports it to the suction mouth. The dredged material is usually sucked up by a wear-resistant centrifugal pump and discharged either through a pipe line or to a barge. Cutter-suction dredgers are most often used in geological areas consisting of hard surface materials (for example gravel deposits or surface bedrock) where a standard suction dredger would be ineffective. They can, if sufficiently powerful, be used instead of underwater blasting.<ref>{{cite web | url=https://www.marinelog.com/index.php?option=com_k2&view=item&id=25244:deme-orders-worlds-most-powerful-cutter-suction-dredge&Itemid=257 | title=DEME orders world's most powerful cutter suction dredge | publisher=Marine Log | date=1 March 2017 | access-date=13 November 2018}}</ref>

{{As of|2024}}, the most powerful cutter-suction dredger in the world is [[DEME]]'s [[Spartacus (ship)|''Spartacus'']], which entered service in 2021.<ref>{{cite web | url=https://www.deme-group.com/news/deme-takes-delivery-spartacus-most-powerful-and-innovative-cutter-suction-dredger-world | title=DEME Takes Delivery of 'Spartacus' – The Most Powerful and Innovative Cutter Suction Dredger in the World | date=4 August 2021}}</ref>

====Auger suction====
The '''auger dredge system''' functions like a cutter suction dredger, but the cutting tool is a rotating [[Archimedean screw]] set at right angles to the suction pipe. Mud Cat invented the auger dredge in the 1970s.<ref>{{Cite web|url=http://www.mudcatdredge.com/our-history/|title = Mud Cat Dredges - Careers & Job Opportunities with Mud Cat}}</ref>

====Jet-lift====
These use the [[Venturi effect]] of a concentrated high-speed stream of water to pull the nearby water, together with bed material, into a pipe.

====Air-lift====
An [[Airlift (dredging device)|airlift]] is a type of small suction dredge. It is sometimes used like other dredges. At other times, an airlift is handheld underwater by a [[underwater diving|diver]].<ref name=RRR4672>{{cite book |author=Robbins, R |chapter=USAP Surface-Supplied Diving |editor=Lang, MA |editor2=Smith, NE |title=Proceedings of Advanced Scientific Diving Workshop |publisher=Smithsonian Institution |location=Washington, DC |year=2006 |chapter-url=http://archive.rubicon-foundation.org/4672 |access-date=5 April 2013 |archive-date=26 May 2014 |archive-url=https://web.archive.org/web/20140526013827/http://archive.rubicon-foundation.org/xmlui/handle/123456789/4672 |url-status=dead }}</ref> It works by blowing air into the pipe, and that air, being lighter than water, rises inside the pipe, dragging water with it.

===Mechanical dredgers ===
[[Image:Dredging technique schematic.png|thumb|Bucket dredging]]
Some bucket dredgers and grab dredgers are powerful enough to rip out coral to make a shipping channel through [[coral reef]]s.<ref name=mechanical>{{cite web |title=Mechanical Dredger |url=https://www.european-dredging.eu/Mechanical_dredger |website=www.european-dredging.eu |access-date=4 July 2018}}</ref>
[[File:ErfgoedLeiden LEI001016474 Baggervaartuig Hollandsch Diep 4..jpg|thumb|Old Dutch bucket dredging vessel ''Hollandsch Diep 4'']]

====Bucket dredgers====
A [[bucket (machine part)|bucket]] dredger is equipped with a bucket dredge, which is a device that picks up [[sediment]] by mechanical means, often with many circulating buckets attached to a wheel or [[Bucket chain excavator|chain]].<ref name=mechanical/>

====Grab dredgers====
[[File:Dredging the Gowanus Canal (05880).webm|thumb|A [[grab (tool)|grab]] dredger working in the [[Gowanus Canal]], a [[Superfund]] site in [[Brooklyn, New York City]]]]
A [[Grab (tool)|grab]] dredger picks up seabed material with a [[Clamshell bucket|clam shell bucket]], which hangs from an onboard crane or a [[crane barge]], or is carried by a hydraulic arm, or is mounted like on a [[dragline]]. This technique is often used in excavation of [[bay mud]]. Most of these dredges are crane barges with '''spuds''', steel piles that can be lowered and raised to position the dredge.<ref name=mechanical/>

====Backhoe/dipper dredgers====
A backhoe/dipper dredger has a [[backhoe]] like on some [[excavator]]s. A crude but usable backhoe dredger can be made by mounting a land-type backhoe excavator on a [[Pontoon (boat)|pontoon]]. The six largest backhoe dredgers in the world are currently the Vitruvius, the Mimar Sinan, Postnik Yakovlev (Jan De Nul), the Samson (DEME), the Simson and the Goliath (Van Oord).{{Citation needed|date=May 2010}} They featured [[barge]]-mounted excavators. Small backhoe dredgers can be track-mounted and work from the bank of ditches. A backhoe dredger is equipped with a half-open shell. The shell is filled moving towards the machine. Usually dredged material is loaded in barges. This machine is mainly used in harbours and other shallow water.<ref name=mechanical/>

'''Excavator dredge attachments'''

The excavator dredge attachment uses the characteristics of cutter-suction dredgers, consisting of cutter heads and a suction pump for transferring material. These hydraulic attachments mount onto the boom arm of an excavator allowing an operator to maneuver the attachment along the shoreline and in shallow water for dredging.

====Bed leveler====
[[File:Bertha being demonstrated on the Exeter Canal Basin - geograph.org.uk - 1055804.jpg|thumb|Steam dredger ''[[Bertha (drag boat)|Bertha]]'', built 1844, on a demonstration run in 1982]] This is a bar or blade which is pulled over the seabed behind any suitable ship or boat. It has an effect similar to that of a [[bulldozer]] on land. The chain-operated steam dredger ''[[Bertha (drag boat)|Bertha]]'', built in 1844 to a design by [[Isambard Kingdom Brunel|Brunel]] and {{asof|2009|lc=y}} was the oldest operational steam vessel in Britain, was of this type.<ref>{{cite web|url=http://www.worldofboats.org/boats/view/bertha/21/bertha|title=Bertha|work=World of Boats|publisher=Eyemouth Marine Centre|access-date=27 December 2009|location=[[Eyemouth]], Scotland|url-status=dead|archive-url=https://web.archive.org/web/20110604060413/http://www.worldofboats.org/boats/view/bertha/21/bertha|archive-date=4 June 2011}}</ref>

====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 the Dutch word for "scratcher".<ref>https://www.researchgate.net/publication/360967741_Sediment_deficit_and_morphological_change_of_the_Rhine-Meuse_river_mouth_attributed_to_multi-millennial_anthropogenic_impacts#pf7</ref>

====Water injection==== 
<!--How to classify?-->
A water injection dredger (WID) uses a small jet to inject water under low pressure (to prevent the sediment from exploding into the surrounding waters) into the seabed to bring the sediment in suspension, which then becomes a [[turbidity current]], which flows away down slope, is moved by a second burst of water from the WID or is carried away in natural currents. Water injection results in a lot of sediment in the water which makes measurement with most hydrographic equipment (for instance: singlebeam echosounders) difficult.
{{Further|Dredge valve}}

====Pneumatic====
These dredgers use a chamber with inlets, out of which the water is pumped with the inlets closed. It is usually suspended from a crane on land or from a small pontoon or barge. Its effectiveness depends on depth pressure.{{citation needed|date=July 2018}}

====Snagboat====
{{Main|Snagboat}}

A [[snagboat]] is designed to remove big debris such as dead trees and parts of trees from North America waterways.{{citation needed|date=July 2018}}

====Amphibious====
Some of these are any of the above types of dredger, which can operate normally, or by extending legs, also known as spuds, 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. [[Oliver Evans]] (1755–1819) in 1804 invented the Oruktor Amphibolos, an amphibious dredger which was America's first steam-powered road vehicle.<ref>{{cite book| last1 = Evans| first1 = Harold | last2 = Buckland | first2 = Gail | last3 = Lefer | first3 = David | year = 2006 | title = They Made America: From the Steam Engine to the Search Engine: Two Centuries of Innovators | publisher = Back Bay Books | location = Boston, MA | isbn = 0-316-01385-4 | ref = {{sfnRef|Evans, Buckland & Lefer}} | url = https://archive.org/details/theymadeamericaf00haro }}</ref>

====Submersible====
These are usually used to recover useful materials from the seabed. Many of them travel on [[continuous track]]. A unique variant<ref>{{cite web|url=http://www.nio.org/past_events/inchoe/dredging_eia.jsp#dredging_1 |title=National Institute of Oceanography, India |access-date=14 June 2013 |url-status=dead |archive-url=https://web.archive.org/web/20090112162856/http://www.nio.org/past_events/inchoe/dredging_eia.jsp#dredging_1 |archive-date=12 January 2009 }}</ref> is intended to walk on legs on the seabed.<ref>"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</ref>

====Fishing====
{{main|Fishing dredge}}[[File:Dedge haul including live clams and empty shells.jpg|thumb|Dredge haul including live clams and empty shells]]

Fishing dredges are used to collect various species of [[clam]]s, [[scallop]]s, [[oyster]]s or [[mussel]]s from the seabed. Some dredges are also designed to catch crabs, sea urchins, sea cucumbers, and conch. These dredges have the form of a scoop made of chain mesh, and are towed by a [[fishing boat]]. Clam-specific dredges can utilize hydraulic injection to target deeper into the sand.<ref>{{Cite web|url=http://safinacenter.org/2015/05/fishing-gear-101-dredges-the-bottom-scrapers/|archive-url=https://web.archive.org/web/20150526080221/http://safinacenter.org/2015/05/fishing-gear-101-dredges-the-bottom-scrapers/|url-status=dead|archive-date=26 May 2015|title=Fishing Gear 101: Dredges – The Bottom Scrapers|author=Kristjan F. Olgeirsson|date=19 May 2015|website=The Safina Center|language=en-US|access-date=2019-09-21}}{{clarify|reason=archived copies of  this url have a different author|date=October 2020}}</ref> Dredging can be destructive to the seabed and some scallop dredging has been replaced by collecting via [[scuba diving]].<ref name=SPUMS1991>{{cite journal |author=Walker, Margaret |title=What price Tasmanian scallops? A report of morbidity and mortality associated with the scallop diving season in Tasmania 1990. |journal=South Pacific Underwater Medicine Society Journal |year=1991 |volume=21 |issue=1 |url=http://archive.rubicon-foundation.org/9414 |access-date=16 July 2013 |archive-date=20 October 2013 |archive-url=https://web.archive.org/web/20131020041442/http://archive.rubicon-foundation.org/xmlui/handle/123456789/9414 |url-status=usurped }}</ref>

===Notable individual dredgers===
{{main|:Category:Dredgers}}
[[File:Dredger near the Dumbarton Bridge in California.JPG|thumb|[[Mallard II]] near the [[Dumbarton Bridge (California)|Dumbarton Bridge]] in 2021]]
As of June 2018, the largest dredger in Asia is {{MV|Tian Kun Hao}}, a {{convert|140|m|adj=on}} long dredger constructed in China, with a capacity of {{convert|6000|m3/hour}}.<ref name="xin">{{cite news |title=Asia's largest dredging vessel completes first sea trial |url=http://www.xinhuanet.com/english/2018-06/12/c_137249426_2.htm |archive-url=https://web.archive.org/web/20180613111953/http://www.xinhuanet.com/english/2018-06/12/c_137249426_2.htm |url-status=dead |archive-date=13 June 2018 |access-date=13 June 2018 |publisher=Xinhua |date=12 June 2018}}</ref>  An even larger dredger, retired in 1980, was the U.S. Army Corps of Engineers {{ship|USAV|Essayons|1949 ship|2}}, which was {{Convert|525.17|ft|m}} long.<ref>{{Cite book|url=http://hdl.handle.net/2027/uiug.30112008445915|title=The hopper dredge; its history, development and operation|series=Its Engineer manual, EM 1110-2-1410|publisher=Government Printing Office|year=1954|editor-last=Scheffauer|editor-first=Frederick C.|location=Washington, D.C.|hdl=2027/uiug.30112008445915}}</ref> The {{ship||Mallard II}}, a clamshell dredger that maintains [[levee]]s in [[San Francisco Bay]], has operated continuously since being built in 1936.<ref name="bcdc">{{cite web|url=https://bcdc.ca.gov/planning/reports/SaltPonds_Jun2005.pdf|title=Staff Report: Salt Ponds|publisher=San Francisco Bay Conservation and Development Commission|date=October 2005|access-date=2021-07-06|archive-date=2021-07-09|archive-url=https://web.archive.org/web/20210709183519/https://bcdc.ca.gov/planning/reports/SaltPonds_Jun2005.pdf|url-status=live}}</ref><ref name="twenty">{{cite web|url=https://www.southbayrestoration.org/sites/default/files/documents/2003.007.03edenlanding2020.12.18_bcdcoriginal_1.pdf|title=BCDC Permit NO. 2003.007.03|author=San Francisco Bay Conservation and Development Commission|publisher=California Department of Fish and Wildlife|date=2020-12-18}}</ref>{{rp|61}}

===Dredge monitoring software===
Dredgers are often equipped with dredge monitoring software to help the dredge operator position the dredger and monitor the current dredge level. The monitoring software often uses [[Real Time Kinematic]] satellite navigation to accurately record where the machine has been operating and to what depth the machine has dredged to.{{citation needed|date=August 2015}}