Dredging
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Dredging is the process by which either new waterways are created or existing waterways are deepened. By dredging, the water channels or waterways are rendered fit for navigation by ships. Normally, dredging is carried out to build new water channels to seaports or maintain existing water channels to seaports. Dredging is carried out by using special ships and equipment called dredges.
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Types of Dredging
Dredging is normally classified into two types.
Capital dredging is carried out initially to create a new seaport/waterway. Usually, cutter-suction dredges (CSD) are utilized to carry out capital dredging. CSDs are floating platforms with the necessary equipment to carry out dredging. The dredge has a huge tool called a cutter. The cutter is nothing but a big pipe with a cutter head at the end. This rod can be swung and rotated. When it is brought in contact with the earth bed, it loosens the earth. The mix of mud and sand, called slurry, formed by the loosening of earth, is sucked up by the cutter, with the help of huge dredge pumps. This slurry is then deposited on nearby land by pipes, or it is dumped in barges (also referred to as "scows") and then deposited in the deep sea. Cutter-suction dredges can be stationary or self-propelled.
The navigable seaports and waterways become silted with the passage of time, due to the sand and mud deposited by water currents. This causes the draft (depth) of the seaport or waterway to become shallower, rendering the waterways unfit for navigation. Maintenance dredging is thus needed again to increase the depth and maintain the navigability of the waterway. Trailer Suction Hopper Dredges (TSHD), or more commonly referred to as hopper dredges, are usually utilized to carry out maintenance dredging. The operate in a fashion similar to vacuum cleaners. TSHDs are nothing but ships equipped with suction pipes and a large hollow space called a hopper. The hoppers have doors at bottom which can be opened. The maintenance dredging operation consists of lowering the suction pipe onto the sea bed, and the dredge pumps are then engaged and the dredge is slowly moved along the path that needs to be deepened. The suction pipes suck up the slurry from the sea bed and deposit it in the hopper. The excess water in the slurry is spilled off by a simple sedimentation process; 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 slurry that can be carried in one load. Once the hopper is filled with slurry, the suction pipes are lifted up. The TSHD then sails to a dump site and opens the bottom hopper doors, located on the bottom of the hull, disposing off the slurry. Then it returns again to the dredging area to carry on with further dredging, repeating the process until the job is completed.
Largest Dredging Companies in the world
- Van Oord Dredging and Marine Contractors bv
- Dredging Corporation of India Limited
- Dredging International
- Great Lakes Dredge & Dock
- Jan de Nul
- Royal Boskalis Westminster nv
See also
External links
- Central Dredging Association (http://www.dredging.org/)
- Dredging Corporation of India Limited (http://www.dredge-india.com/)
- Dredging International (http://www.dredging.com/)
- Great Lakes Dredge and Dock Co. (http://www.gldd.com/)
- International Association of Dredging Companies (http://www.iadc-dredging.com/)
- Jan de Nul (http://www.jandenul.com/)
- Royal Boskalis Westminster nv (http://www.boskalis.com/)
- Van Oord Dredging (http://www.vanoord.com/)