For the German municipality, see Dreggers. Dredging is an excavation activity usually carried out underwater, in shallow seas or freshwater areas with the purpose of gathering up bottom sediments and disposing of them at a different location. This technique is often used to keep waterways navigable. It is also used as a way to replenish sand on some public beaches, where sand has been lost because of coastal erosion. Dredging is also used as a technique for fishing for certain species of edible clams and crabs (see fishing dredge). Rohde Nielsen A/S - Nyhavn 20 - DK1051 Copenhagen K Phone: +45 33 91 25 07 - E-mail: [email protected] Certification: ISM/ISPS/MLC - ISO 9001:2008 - ISO14001:2004 - VCA **.Capital: dredging carried out to create a new harbor, 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: work and excavation for future bridges, piers or docks/wharves, often connected with foundation work. Maintenance: dredging to deepen or maintain navigable waterways or channels which are threatened to become silted with the passage of time, due to sedimented 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 reservoirs 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. 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, which can be eroded by human activity or by storms. This is typically performed by a cutter- suction dredge or trailing suction hopper dredge. Harvesting materials: dredging sediment for elements like gold, diamonds or other valuable trace substances. Seabed mining: a possible future use, recovering natural metal ore nodules from the sea's abyssal plains. Construction materials: dredging sand and gravels from offshore licensed areas for use in construction industry, principally for use in concrete. Very specialist industry focused in NW Europe using specialized trailing suction hopper dredgers self discharging dry cargo ashore. Anti- eutrophication: Dredging is an expensive option for the remediation of eutrophied (or de- oxygenated) water bodies. 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. Contaminantremediation: to reclaim areas affected by chemical spills, storm water surges (with urban runoff), and other soil contaminations. Disposal becomes a proportionally large factor in these operations. Removing trash and debris: often done in combination with maintenance dredging, this process removes non- natural matter from the bottoms of rivers and canals and harbors. Flood prevention: this can help to increase channel depth and therefore increase a channel's capacity for carrying water. Peat extraction: in former times, so- called dredging poles or dredge hauls were used on the back of small boats to manually dredge the beds of peat- moor waterways before extracting the peat for use as a fuel. This tradition has now become more or less obsolete and the tools used to do this have also changed significantly. Oyster dredging or harvesting: in Louisiana and other states with salt water estuaries that can sustain bottom oyster beds. A heavy metal rectangular scoop device is towed astern of a moving boat with a chain bridle attached to a cable and winch which scoops up oysters as it drags along the bottom. One of our smallest dredgers. This dredge has been designed for shallow dams ranging from 1 to 3 meters. Suitable for plastic-lined dams and small operations or where a restricted discharge is required. A versatile dredge with. About the Dry Dredgers. Contact Us What We Do A Brief History of the Dry Dredgers By-laws of Dry Dredgers, Inc. The Dry Dredgers is an association of amateur geologists dedicated to the knowledge and enjoyment of. Rocky Mountain Mining Rights. Please check out this great communication network for miners. MINERS COMMUNICATION NETWORK. Bureau of Land Management's Land & Mineral Legacy Rehost 2000 System. About Union Dredgers and Marine Contracting Union Dredgers and Marine Contracting (UDMC) is a member of the Union Group of Companies, a group of local companies active in the UAE market since 2001. Established in 2007 UDMC. The device is periodically hauled aboard and the oysters in it are sorted and bagged for shipment to an oyster processing facility. As a hobby: hobbyists examine their dredged matter to pick out items of potential value, similar to the hobby of metal detecting, or the hobby form of dumpster diving, on land. Relevance. Recreational boating also would be constrained to the smallest vessels. The majority of marine dredging operations (and the disposal of the dredged material) will require that appropriate licences are obtained from the relevant regulatory authorities, and dredging is usually carried out by (or for) harbour companies or corresponding government agencies. Types of dredging vessels. This is often the most commonly used form of dredging. 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. The largest trailing suction hopper dredgers in the world are currently Jan De Nul's Cristobal Colon (launched 4 July 2. Main design specs for the Cristobal Colon and the Leiv Eriksson are: 4. 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. In recent years, dredgers with more powerful cutters have been built in order to excavate harder rock without the need for blasting. The two largest cutter suction dredgers in the world are currently (as at August 2. DEME's D'Artagnan (2. W total installed power). The first widely used auger dredges were designed in the 1. Mud Cat Dredges, which was run by National Car Rental, but is now a Division of Ellicott Dredges. In 1. 99. 6, IMS Dredges introduced a self- propelled version of the auger dredge that allows the system to propel itself without the use of anchors or cables. During the 1. 98. Today, auger dredges are used for a wider variety of applications including river maintenance and sand mining. The most common auger dredge on the global market today is the Versi- Dredge. The turbidity shroud on auger dredge systems creates a strong suction vacuum, causing much less turbidity than conical (basket) type cutterheads and so they are preferred for environmental applications. The vacuum created by the shroud and the ability to convey material to the pump faster makes auger dredge systems more productive than similar sized conical (basket) type cutterhead dredges. Jet- lift. It is sometimes used like other dredges. At other times, an airlift is handheld underwater by a diver. Some bucket dredgers and grab dredgers are powerful enough to rip out coral to make a shipping channel through coral reefs. Clamshell. This technique is often used in excavation of bay mud. Most of these dredges are crane barges with spuds. Backhoe/dipper. A crude but usable backhoe dredger can be made by mounting a land- type backhoe excavator on a pontoon. The six largest backhoe dredgers in the world are currently the Vitruvius, the Mimar Sinan, Postnik Jakovlev (Jan De Nul), the Samson (DEME), the Simson and the Goliath (Van Oord). 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 harbors and other shallow water. Water injection. Water injection results in a lot of sediment in the water which makes measurement with most hydrographic equipment (for instance: singlebeam echosounders) difficult. Pneumatic. It is usually suspended from a crane on land or from a small pontoon or barge. Its effectiveness depends on depth pressure. Bed leveler. It has an effect similar to that of a bulldozer on land. The chain- operated steam dredger Bertha, built in 1. Brunel and now the oldest operational steam vessel in Britain, was of this type. 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 . 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. Submersible. Many of them travel on continuous track. These dredges have the form of a scoop made of chain mesh, and are towed by a fishing boat. Careless dredging can be destructive to the seabed. Nowadays some scallop dredging is replaced by collecting via scuba diving. The bodies may be murder victims, or people who committed suicide by drowning, or victims of accidents. It is sometimes pulled by people walking on the bank. Search and rescue units also often use this type of dredge in searching for bodies of missing persons. Disposal of materials. 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.
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