Examine individual changes

'{{Redirect|Dredge}} {{Redirect|Dredgers|the German municipality|Dreggers}} {{Use dmy dates|date=March 2015}} {{EngvarB|date=July 2018}} {{Use dmy dates|date=January 2018}} [[File:Dredge (PSF).png|thumb|A grab dredge]] '''Dredging''' is the operation of removing material from one part of the water environment and relocating it to another. In all but a few situations the excavation is undertaken by a specialist floating plant, known as a dredger. Dredging is carried out in many different locations and for many different purposes, but the main objectives are usually to recover material that has some value or use, or to create a greater depth of water.<ref name="About">{{cite web |title=EuDA - About dredging - Dredging |url=https://www.european-dredging.eu/Dredging |website=www.european-dredging.eu |accessdate=3 July 2018 |language=en}}</ref> ==Description== Dredging is the form of [[Earthworks (engineering)|excavation]] carried out underwater or partially underwater, in shallow waters or [[ocean dredging|ocean waters]]. It keeps waterways and ports navigable, and assists coastal protection, land reclamation and coastal redevelopment, by gathering up bottom [[sediment]]s and transporting it elsewhere. Dredging can be done to recover materials of commercial value; these may be high value minerals or sediments such as sand and gravel that are used by the construction industry.<ref name=rabobank/> Dredging is a four-part process: loosening the material, bringing the material to the surface (together extraction), transportation and disposal. <ref name="About"/> The material can be brought to the surface causing I am a hacker me doods by suction or mechanical means.<ref name="About"/> The extract can be disposed of locally or transported by barge or in a liquid suspension in kilometre long pipelines. Disposal can be to infill sites, or the material can this funny lmao be used constructively to replenish eroded sand that has been lost lol I like hacking its fun to [[coastal erosion]], or constructively create sea-walls, building land <ref name="About"/> or [[MV Tian Kun Hao|whole new landforms]] such as viable islands in [[coral atoll]]s.<ref name=TianKunHao>{{cite news |title=What is China's 'magic island-making' ship? |url=https://www.bbc.co.uk/news/world-asia-china-41882081 |accessdate=4 July 2018 |work=BBC News |date=6 November 2017}}</ref> ==History== Ancient authors refer to habour dredging. The seven arms of the Nile were channelled and wharfs built at the time of the pyramids (4000 BC), there was extensive harbour building in the eastern Mediterranean from 1000 BC and the disturbed sediment layers gives evidence of dredging. At Marseille, dredging phases are recorded from the third century BC onwards, the most extensive during the first century AD. The remains of three dredging boats have been unearthed; they were abandoned at the bottom of the harbour during the first and second centuries AD.<ref name="MMC">{{cite web |last1=Morhange |first1=Christophe |last2=Marriner |first2=Nick |last3=Carayon |first3=Nicolas |title=The eco-history of ancient Mediterranean harbours |url=https://www.ancientportsantiques.com/wp-content/uploads/Documents/AUTHORS/Morhange-PublGenerales/Morhange2016-HistoryPorts.pdf|accessdate=1 July 2018}}</ref> Dredging machines were used during the construction of the [[Suez Canal Company|Suez Canal]]. [[File:Draga cavafango Leonardo - Museo scienza e tecnologia Milano.jpg|thumb]] [[File:Draga cavafango Leonardo 2 - Museo scienza e tecnologia Milano.jpg|thumb|Reconstruction of the mud-drag by [[Leonardo da Vinci]] (''Manuscript E, folio 75 v.'') <!--on exhibit at the [[Museo Nazionale della Scienza e della Tecnologia "Leonardo da Vinci"|Museo nazionale della scienza e della tecnologia "Leonardo da Vinci"]], Milan.-->]] During the renaissance da Vinci drew a design for a drag dredger. <!-- Ancient History (4241 B.C. TO AD. 500) The Period Of Stagnation (A.D. 500-1500) The Awakening Of Interest (c. A.D. 1500-1700) The Age Of Invention (A.D. 1700-1800) The Age Of Steam Power (A.D. 1800-1900) The Twentieth Century <ref>{{cite book |title=ICE Virtual Library |url=https://www.icevirtuallibrary.com/doi/abs/10.1680/d1967c.44777.0002 |accessdate=2 July 2018 |language=en}}</ref> --> ==Purposes of dredging== * '''Maintenance''': dredging to deepen or maintain navigable [[waterway]]s or [[Channel (geography)|channels]] which are threatened to become silted with the passage of time, due to [[sediment]]ed sand and mud, possibly making them too shallow for navigation. This is often carried out with a trailing suction hopper dredge. Most dredging is for this purpose, and it may also be done to maintain the holding capacity of [[reservoir]]s or lakes. * '''[[Land reclamation]]''': dredging to mine sand, clay or rock from the seabed and using it to construct new land elsewhere. This is typically performed by a cutter-suction dredge or trailing suction hopper dredge. The material may also be used for [[flood]] or [[erosion]] control. * '''Capital dredging''': dredging carried out to create a new [[harbour]], [[Berth (moorings)|berth]] or [[waterway]], or to deepen existing facilities in order to allow larger ships access. Because capital works usually involve hard material or high-volume works, the work is usually done using a cutter suction dredge or large trailing suction hopper dredge; but for rock works, drilling and blasting along with mechanical excavation may be used. * '''Preparatory''': dredging work and excavation for future [[bridge]]s, [[pier]]s or [[Dock (maritime)|docks]] or [[Wharf|wharves]], This is often to build the [[Foundation (architecture)|foundations]]. * '''Winning construction materials''': dredging sand and gravels from offshore licensed areas for use in construction industry, principally for use in concrete. This very specialist industry is focused in NW Europe, it uses specialized trailing suction hopper dredgers self discharging the dry cargo ashore. * '''[[Soil contamination|Contaminant]] [[Environmental remediation|remediation]]''': to reclaim 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. * '''[[Flood prevention]]''': dredging increases the channel depth and therefore increase a channel's capacity for carrying water. * '''[[Fishing dredger|Fishing dredging]]''' is a technique for catching certain species of edible [[clam]]s and [[crab]]s. In Louisiana and other American states, with salt water estuaries that can sustain bottom [[oyster bed]]s, oysters are raised and harvested. A heavy rectangular metal scoop is towed astern of a moving boat with a chain bridle attached to a cable. This drags along the bottom scooping up oysters. It is periodically winched aboard and the catch is sorted and bagged for shipment.<ref name="reasons"/> ===Other=== * '''Harvesting materials''': dredging [[sediment]] for elements like [[gold]], [[diamond]]s or other valuable trace substances. Hobbyists examine their dredged matter to pick out items of potential value, similar to the [[Coin shooting|hobby of metal detecting]]. <!-- Look again --> * '''[[Beach nourishment]]''': this is mining sand offshore and placing on a beach to replace sand eroded by storms or wave action. This enhances the recreational and protective function of the beach, which are also eroded by human activity. This is typically performed by a cutter-suction dredge or trailing suction hopper dredge. {{citation needed|date=July 2018}} * '''[[Peat extraction]]''': ''dredging poles'' or ''dredge hauls'' were used on the back of small boats to manually dredge the beds of [[peat]]-[[Moorland#Heather moorland|moor]] waterways. The extracted peat was used as a fuel. This tradition is now more or less obsolete. The tools are now significantly changed.{{citation needed|date=July 2018}} * '''Removing rubbish and debris''': often done in combination with maintenance dredging, this process removes non-natural matter from the bottoms of rivers and canals and harbours. {{anchor|Police drag}}Law enforcement agencies sometimes need to use a 'drag' to recover evidence or corpses from beneath the water. * '''[[eutrophication|Anti-eutrophication]]''': A kind of contaminant remediation, dredging is an expensive option for the remediation of eutrophied (or de-oxygenated) water bodies; one of the causes is like mentioned above, [[sewage sludge]]. However, as artificially elevated phosphorus levels in the sediment aggravate the eutrophication process, controlled sediment removal is occasionally the only option for the reclamation of still waters.{{citation needed|date=July 2018}} * '''Seabed mining''': is a possible future use, recovering natural metal [[ore]] nodules from the sea's [[abyssal plain|deepest troughs]].<ref name="reasons">{{cite web |title=EuDA - About dredging - Dredging - Reasons for Dredging |url=https://www.european-dredging.eu/Reasons_for_Dredging |website=www.european-dredging.eu |accessdate=3 July 2018 |language=en}}</ref> ==Types of dredgers== ===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]], [[Warsaw]], [[Poland]]]] [[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")]] :''For suction-type excavation out of water, see [[Suction excavator]].'' These operate by sucking through a long tube like some of the basic hoes , 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. This is often the most commonly used form of dredging.{{Citation needed|date=August 2007}} ====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}} The largest trailing suction hopper dredgers in the world are currently [[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 |accessdate=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 |accessdate=14 June 2013}}</ref>). Main design specs 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 |accessdate=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. <!-- Deleted image removed: [[Image:XLarge cutterhead.jpg|left|thumb|Replaceable pin tooth cutter head used on the largest cutter suction dredges manufactured by Ellicott Dredges]] --> ====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 | accessdate=13 November 2018}}</ref> As of 2018, the most powerful cutter-suction dredger in the world is [[DEME]]'s [[Spartacus (ship)|''Spartacus'']], which is scheduled to enter service in 2019.<ref>{{cite web | url=https://www.bairdmaritime.com/work-boat-world/marine-projects-world/1245-construction-of-world-s-most-powerful-csd-starts-with-keel | title=Keel laying signals start of world’s most powerful CSD | publisher=Baird Maritime | date=21 December 2017 | accessdate=13 November 2018}}</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. The first widely used auger dredges were designed in the 1980s. In 1996, IMS Dredges introduced a self-propelled version operates without anchors or cables. They were primarily used for sludge removal applications from waste water treatment plants; since then they have been used river maintenance and sand mining.{{citation needed|date=July 2018}} The turbidity shroud on auger dredge systems creates a strong suction vacuum, causing otters to be cute and much less turbidity than conical (basket) type cutterheads and so they are preferred for environmental applications. This and the ability to convey material to the pump faster makes auger dredge systems more productive than similar sized conical (basket) type cutterhead dredges.{{citation needed|date=July 2018}} ====Jet-lift==== These use the [[Venturi effect]] of a concentrated high-speed stream of water to suck the nearby water, I am a hacker me doods, 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 journal |author=Robbins, R |title=USAP Surface-Supplied Diving. |journal=In: Lang, MA and Smith, NE (eds.). Proceedings of Advanced Scientific Diving Workshop: February 23–24, 2006, Smithsonian Institution, Washington, DC. |year=2006 |url=http://archive.rubicon-foundation.org/4672 |accessdate=5 April 2013}}</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 |accessdate=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==== [[Image:Grab Dredging Process.JPG|thumb|Grab (clamshell) dredging in process in [[Port Canaveral]], [[Florida]]]] 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/> ====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 now 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|accessdate=27 December 2009|location=[[Eyemouth]], Scotland|deadurl=yes|archiveurl=https://web.archive.org/web/20110604060413/http://www.worldofboats.org/boats/view/bertha/21/bertha|archivedate=4 June 2011|df=dmy-all}}</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". ====Water injection==== <!--How to classify?--> A water injection dredger 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. ====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. {{citation needed|date=July 2018}} ====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 |publisher=Web.archive.org |date= |accessdate=14 June 2013 |deadurl=yes |archiveurl=https://web.archive.org/web/20090112162856/http://www.nio.org/past_events/inchoe/dredging_eia.jsp#dredging_1 |archivedate=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==== [[File:Dedge haul including live clams and empty shells.jpg|thumb|Dredge haul including live clams and empty shells]] [[Fishing dredge]]s are used to collect various species of [[clam]]s, [[scallop]]s, [[oyster]]s or [[crab]]s from the seabed. These dredges have the form of a scoop made of chain mesh, and are towed by a [[fishing boat]]. 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 |accessdate=16 July 2013 }}</ref> ===Notable individual dredgers=== ====A large Asian dredger==== As of June 2018, the largest dredger in Asia is "''[[MV Tian Kun Hao]]''", a 140 metres long dredger constructed in China, with a capacity of 6,000 cubic meters per 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 |accessdate=13 June 2018 |publisher=Xinhua |date=12 June 2018}}</ref> ===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}} ==Transportation and disposal of materials== In a "hopper dredger", the dredged materials end up in a large onboard hold called a "hopper." A suction hopper dredger is usually used for maintenance dredging. A hopper dredge usually has doors in its bottom to empty the dredged materials, but some dredges empty their hoppers by splitting the two halves of their hulls on giant hydraulic hinges. Either way, as the vessel dredges, excess water in the dredged materials is spilled off as the heavier solids settle to the bottom of the hopper. This excess water is returned to the sea to reduce weight and increase the amount of solid material (or slurry) 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 empties its hopper.{{citation needed|date=July 2018}} Some hopper dredges are designed so they can also be emptied from above using pumps if dump sites are unavailable or if the dredge material is contaminated. Sometimes the slurry of dredgings and water is pumped straight into pipes which deposit it on nearby land. These pipes are also commonly known as [https://max-groups.com/products/discharge-dredging-dredge-hose/ dredge hoses], too. There are a few different types of dredge hoses that differ in terms of working pressure, float-ability, armored or not etc. Suction hoses, discharge armored hoses and self-floating hoses are some of the popular types engineered for transporting and discharging dredge materials.<ref>{{Cite web|url=https://max-groups.com/products/discharge-dredging-dredge-hose/|title=Dredging & Discharge: Dredge Hoses|website=Max Groups Marine|language=en-US|access-date=2019-01-08}}</ref> Some even had the pipes or hoses customised to exact dredging needs etc. Other times, it is pumped into [[barge]]s (also called [[scow]]s), which deposit it elsewhere while the dredge continues its work.{{citation needed|date=July 2018}} A number of vessels, notably in the UK and NW Europe de-water the hopper to dry the cargo to enable it to be discharged onto a quayside 'dry'. This is achieved principally using self discharge bucket wheel, drag scraper or excavator via conveyor systems.{{citation needed|date=July 2018}} When contaminated (toxic) sediments are to be removed, or large volume inland disposal sites are unavailable, dredge slurries are reduced to dry solids via a process known as dewatering. Current dewatering techniques employ either centrifuges, Geotube containers, large textile based filters or polymer [[flocculant]]/congealant based apparatus.{{citation needed|date=July 2018}} In many projects, slurry dewatering is performed in large inland settling pits, although this is becoming less and less common as mechanical dewatering techniques continue to improve.{{citation needed|date=July 2018}} 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.{{citation needed|date=July 2018}} The proper management of contaminated sediments is a modern-day issue of significant concern. Because of a variety of maintenance activities, thousands of tonnes of contaminated sediment are dredged worldwide from commercial ports and other aquatic areas at high level of industrialization. Dredged material can be reused after appropriate decontamination. A variety of processes has been proposed and tested at different scales of application ([[Environmental remediation#Technologies|technologies for environmental remediation]]). Once decontaminated, the material could well suit the building industry, or could be used for beach nourishment.<ref>{{cite web|last1=Fonti|first1=V|title=To remediate or to not remediate?|url=https://atlasofscience.org/to-remediate-or-to-not-remediate/#more-17692|publisher=Atlas of Science|ref=Fonti, 2016}}</ref> ==Environmental impacts== Dredging can create disturbance to [[aquatic ecosystem]]s, often with adverse impacts.{{Citation needed|date=September 2017}}<ref>{{cite journal | last1 = Newell | first1 = R.C. | last2 = Seiderer | first2 = L.J. | last3 = Hitchcock | first3 = D.R. | year = 1998 | title = The impact of dredging works in coastal waters: A review of the sensitivity to disturbance and subsequent recovery of biological resources on the sea bed | url =http://www.sussex.ac.uk/geography/researchprojects/coastview/dredging/Impact_of_Dredging_Oc_Bio.Ann_Rev.pdf | journal = Oceanography and Marine Biology: An Annual Review | volume = 36 | issue = | pages = 127–178 }}</ref> In addition, dredge spoils may contain [[toxic]] chemicals that may have an adverse effect on the disposal area; furthermore, the process of dredging often dislodges chemicals residing in [[benthic]] substrates and injects them into the [[water column]].{{Citation needed|date=September 2017}} The activity of dredging can create the following principal impacts to the environment: * Release of toxic chemicals (including [[heavy metal (chemistry)|heavy metals]] and [[Polychlorinated biphenyls|PCB]]) from bottom [[sediment]]s into the [[water column]].<ref name="Bridges, T S. 2010">Bridges, T S., Gustavson, K. E., Schroeder, P., Ells, S. J., & Hayes, D. (2010). Dredging processes and remedy effectiveness: Relationship to the 4 Rs of environmental dredging. Integrated Environmental Assessment and Management, 6 (4), 619-630.</ref> * Collection of heavy metals lead left by fishing, bullets, 98% mercury reclaimed [natural occurring and left over from gold rush era].{{Citation needed|date=September 2017}} * Short term increases in [[turbidity]], which can affect aquatic [[species]] [[metabolism]] and interfere with [[spawn (biology)|spawning]]. Suction dredging activity is allowed only during non-spawing time frames set by fish and game (in-water work periods).{{Citation needed|date=September 2017}} * Secondary impacts to [[marsh]] productivity from [[sedimentation]]{{Citation needed|date=September 2017}} * Tertiary impacts to [[bird|avifauna]] which may [[prey]] upon contaminated aquatic organisms{{Citation needed|date=September 2017}} * Secondary impacts to aquatic and benthic organisms' [[metabolism]] and mortality{{Citation needed|date=September 2017}} * Possible contamination of dredge spoils sites<ref name="Bridges, T S. 2010"/> * Changes to the topography by the creation of "spoil islands" from the accumulated spoil{{Citation needed|date=September 2017}} * Releases toxic compound [[Tributyltin]], a popular [[biocide]] used in [[anti-fouling paint]] banned in 2008, back into the water.{{Citation needed|date=September 2017}} The nature of dredging operations and possible environmental impacts cause the industry to be closely regulated and a requirement for comprehensive regional environmental impact assessments with continuous monitoring.{{Citation needed|date=September 2017}} The U.S. [[Clean Water Act]] requires that any discharge of dredged or fill materials into "waters of the United States," including wetlands, is forbidden unless authorized by a permit issued by the [[United States Army Corps of Engineers|Army Corps of Engineers]].<ref>[[Clean Water Act]], {{USC|33|1311}}, {{USC|33|1362}}, {{USC|33|1344}}{{Citation needed|date=September 2017}}</ref> As a result of the potential impacts to the environment, dredging is restricted to licensed areas only with vessel activity monitored closely using automatic GPS systems.{{Citation needed|date=September 2017}} ==Major dredging companies== According to a [[Rabobank]] outlook report in 2013, the largest dredging companies in the world are in order of size <ref name=rabobank>{{cite web|url=http://www.dredging.org/media/ceda/org/documents/resources/othersonline/rabobank-outlook_dredging_september_2013.pdf |title=Dredging: Profit margins expected to remain fairly healthy until 2018 |publisher= |year=2013 |accessdate=2018-03-26}}</ref> * [[China Harbour Engineering]] ([[China]]) * [[Jan De Nul]] ([[Belgium]]) * [[DEME]] (Belgium) * [[Great Lakes Dredge and Dock Company|Great Lakes Dredge & Dock Company]] ([[United States]]) * [[Royal Boskalis Westminster]]([[Netherlands]]) * [[Van Oord Dredging and Marine Contractors]] (Netherlands) Notable dredging companies in North America: * [[Manson Construction Co.]] ([[United States]]) ==Images== <gallery mode="packed"> File:Dredge in the Port of Oakland with San Francisco in the background.JPG |Grab (clamshell) dredge ''Njord'' of the [[Manson Construction Co.]] fleet in the [[Port of Oakland]], California Image:Dredge No-4 (1).JPG|The excavator of a [[Yukon]] dredge. Image:Lakes Entrance Dredger April Hamer.JPG|''April Hamer'' at [[Lakes Entrance]], [[Victoria (Australia)|Victoria]] Australia Image:OrisantDredger.jpg|The ''Orisant'' a trailing suction dredger in the port of [[IJmuiden]], [[Netherlands]] Image:Hong Kong dredger123.jpg|Grab dredging in [[Victoria Harbour]], [[Hong Kong]] Image:Alexander von Humboldt (empty).jpg|''Alexander von Humboldt'' of the [[Jan De Nul]] fleet Image:BurigangaDredge.JPG|Sand mining Image:HR-Morris-Pipeline-Dredge.jpg|''HR Morris'' of the [[Manson Construction Co.]] fleet, a Cutter Suction Pipeline Dredge, working on [[Mission Bay, San Diego, California]] Image:Barge on Neva river.jpg|Dredge ship with barges on [[Neva River|Neva bay]] in [[Saint Petersburg]], [[Russia]] Image:Dredge ship top view - 01.JPG|Top view of a suction dredger on the [[Nandu River]], [[Hainan]], China Image:Cutterhead of dredge Bill Holman Louisville Kentucky USA Ohio River mile 607 July 2002 file a2g092.jpg|Cutterhead of dredge ''Bill Holman'', [[Louisville, Kentucky]], [[United States|USA]], [[Ohio River]] mile 607, July 2002 </gallery> ==See also== {{Portal|UK Waterways|Nautical}} * [[Dredge ball joint]], connection between 2 pipes that are used to transport mixture of water and sand from a dredger to the discharging area * [[Dredge drag head]] * [[Navigability]] * [[Peace in Africa (ship)|''Peace in Africa'' (ship)]], a diamond-mining dredger * [[Queen of the Netherlands (ship)|''Queen of the Netherlands'' (ship)]], a big dredger * [[River engineering]] for inland dredging and other river management systems * [[WT Preston]], a [[snagboat]] ==References== {{Reflist}} ==External links== {{Commons category|Dredge ships}} * [http://www.dredgers.nl/ Directory of Dredgers] (a close to exhaustive private collection of dredger photographs) * [https://web.archive.org/web/20070928020541/http://www.gbrmpa.gov.au/__data/assets/pdf_file/0003/7869/DredgeandSpoil.pdf Dredging and Spoil Disposal Policy] ([[pdf]])(from the [[Government of Australia|Australian Government]]) * [http://www.theartofdredging.com/ The Art of Dredging] (Knowledge sharing) * [https://www2.iadc-dredging.com/subject International Association of Dredging Companies] Knowledge centre * [https://web.archive.org/web/20110604060413/http://www.worldofboats.org/boats/view/bertha/21/bertha World of Boats (EISCA) Collection ~ Isambard Kingdom Brunel's Bertha] {{Industries}} {{ModernMerchantShipTypes}} {{Authority control}} [[Category:Engineering vehicles]] [[Category:Coastal construction]] [[Category:Dredgers]] [[Category:Nautical terminology]] [[Category:Coastal engineering]] [[de:Baggerschiff]]'