Dredging Techniques and dredgers

dredging meaning,uses of dredgers,types of dredgers, major dredging companies,uses of dredgers,backhoe,environmental impacts

1. DREDGING TECHNIQUES MINI PROJECT

2. Dredging is an excavation activity usually carried out underwater, in shallow seas and in freshwater with the purpose of gathering up bottom sediments & widening. It is a technique, often used to keep waterways navigable and creates an anti-sludge pathway for boats. It is also used as a way to replenish sand on some public beaches, where sand has been lost because of coastal erosion. Dredger is an apparatus for bringing up objects,sand or mud from a river or a seabed by scooping & dragging. WHAT DO YOU MEAN BY DREDGING ?

3. Dredger

4. Capital : Dredging is carried out to create a new harbour, berth or waterway ,or to deepen existing facilities in order to allow larger ships access.This work is usually done by using a cutter suction dredge or large trailing suction hopper dredge. Preparatory : This excavation work is prepared for future bridges, piers or docks/wharves, often connected with foundation work. USES OF DREDGERS

5. Maintenance : Dredging maintain navigable waterways or channels which becomes silted with the passage of time, due to sedimented sand and mud,makes them too shallow for navigation. This is often carried out with a trailing suction hopper dredge. Mostly dredging is used for this purpose. Land Reclamation : Dredging to mine sand, clay or rock from the seabed and using it to construct new land elsewhere.This is perform by a cutter-suction dredge or trailing suction hopper dredge. Harvesting materials : Dredging sediment for elements like gold, diamonds or other valuable trace substances.

6. Seabed mining : It can be used probably in future for recovering natural metal ore nodules from the sea abyssal’s plains. Construction materials : Dredging sand and gravels from offshore licensed regions can be used in construction industry, principally for use in concrete. Beach Nourishment: Mining sand offshore and placing on a beach,is used to replace sand eroded by storms or wave action. This is done to enhance the protective function of the beaches.

7. Flood Prevention : This can help to increase channel depth and therefore increase a channel's capacity for carrying water. Contaminant Remediation : To reclaim the 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.

8. Dredgers may be broadly classified into two main types depending upon the method used to transport loosened material from the sea-bed to the water surface. These are : 1. Mechanical dredgers. 2. Hydraulic dredgers. MECHANICAL DREDGER Mechanical dredgers come in a variety of forms, each involving the use of grab or bucket to loosen the in-situ material and raise and transport it to the surface . DIFFERENT TYPES OF DREDGERS

9. A Bucket Dredger is a stationary dredger, fixed on anchors and moved while dredging along semi-arcs by winches. The bucket dredger is one of the oldest types of dredging equipment. It has an endless chain of buckets that is used to scrape over the bottom. 1. BUCKET DREDGER

10. A Grab Dredger is a stationary dredger, moored on anchors or on spud-poles. The dredging tool is a grab normally consisting of two half-shells operated by wires or (electro)-hydraulically. The grab can be mounted on a dragline or on a hydraulic excavator of the backhoe type.  2. GRAB DREDGER

11. A Backhoe Dredger is a stationary dredger, moored on anchors or on spud-poles. A spud is a large pole that can anchor a ship. Small backhoe dredgers can be track mounted and work from the banks of ditches. A backhoe dredger is a hydraulic excavator equipped with a half open shell. 3. BACKHOE DREDGER

12. Hydraulic dredging is most efficient when working with fine materials, because they can easily be held in suspension. Coarser materials and even gravel can be worked but with a greater demand on pump power and with greater wear on pumps and pipes. The principal feature of all dredgers in this category is that the loosened material is raised from its in-situ state in suspension through a pipe system connected to a centrifugal pump.  Dredgers of this type is now widely used. HYDRAULIC DREDGER

13. A Suction Dredger is a stationary dredger used to mine for sand. The suction pipe is pushed vertically into a sand deposit. If necessary water jets help to bring the sand up. It is loaded into barges or pumped via pipeline directly to the reclamation area. 1. SUCTION DREDGER

14. A Cutter Suction Dredger is a stationary dredger which makes use of a cutter head to loosen the material to be dredged. It pumps the dredged material via a pipeline ashore or into barges.  The cutter head can be replaced by several kinds of suction heads for special purposes, such as environmental dredging. 2. CUTTER SUCTION DREDGER

15. A Trailing Suction Hopper Dredger is a self-propelled ship which fills its hold or hopper during dredging, while following a pre-set track. The hopper can be emptied by opening bottom doors ,offloading by pumping its load off ashore. This kind of dredger is mainly used in open water: rivers, canals, and the open sea.Trailing suction hopper dredgers, commonly known simply as ‘hoppers’ or ‘trailers’. 3. TRAILING SUCTION HOPPER DREDGER

16. Barge unloading dredgers are used to transfer material from hopper barges to shore, usually for reclamation. A barge unloader is basically a pontoon supporting a suction pump for the unloading, and a high pressure water pump used to fluidise the barge contents by jetting. The mixture is then pumped through a pipeline to the point of reclamation or relocation. 4. BARGE UNLOADING DREDGER

17. The activity of dredging can create the following principal impacts to the environment: Collection of heavy metals lead left by fishing, bullets, 98% mercury reclaimed [natural occurring and left over from gold rush era]. Short term increases in turbidity, which can affect aquatic species metabolism and interfere with spawning. Suction dredging activity is allowed only during non-spawning time frames set by fish and game (in-water work periods). Secondary impacts to marsh productivity from sedimentation. Tertiary impacts to avifauna which may prey upon contaminated aquatic organisms. Secondary impacts to aquatic and benthic organisms' metabolism and mortality. Possible contamination of dredge spoils sites. Changes to the topography by the creation of "spoil islands" from the accumulated spoil. Releases toxic compound TributyltIn , a popular biocide used in anti-fouling paint banned in 2008, back into the water. ENVIRONMENTAL IMPACTS

18. According to a Rabobank outlook report in 2013, the largest dredging companies in the world are in order of size- China Harbors Engineering (China). Jan De Null (Belgium). DEME (Belgium). Royal Boskalis Westminster(Netherlands). Van Ord Dredging and Marine Contractors(Netherlands). Dredging Corporation of India Limited (Vishakhapatnam, India). MAJOR DREDGING COMPANIES

19. FROM THIS MINI PROJECT WE CAME TO KNOW ABOUT DREDGING,ITS USES,ITS TECHNIQUES,ITS TYPES,ENVIRONMENTAL IMPACTS AND MAJOR DREDGING COMPANIES. NOW- A-DAYS,THERE ARE A LOT OF DREDGERS ARE USED IN CIVIL ENGINEERING PROJECTS. THANK YOU! CONCLUSION