Dredging, as a process, is used to remove the deposits percolated underwater for the purpose of clearing the water pathway for ships to pass; to create adequate space to construct important bridges, dykes and dams and to weed out silt, intoxicants and pollutants from the bottom of the water.
What is Dredging?
Dredging mainly involves carrying out excavation, of either naturally deposited sediments or man-made debris such as rocks, bottom sediments, construction debris, and refuse, and plant or animal matter on the bottom of either shallow seawater or freshwaters. In general terms, dredging implies digging up of the gathered sediments from the seabed and disposing them off at some other site.
The oldest known dredging activities are: dredging for peat excavation and maintenance dredging. Maintenance Dredging is a broader term which includes clearing of deposits and cleaning, widening or deepening of a water body using either a suction or scooping device (generally called a dredger).
Regular maintenance dredging is of huge importance in coastal regions which have large tidal activity and also in water bodies which are susceptible to become silted with sediments, sand and mud. The Lowlands of Netherlands and Flanders are the best example of such regions which require regular maintenance dredging.
For dredging, equipment called dredger is used to remove the deposited sediments from an inlet creek, waterway or ocean floor. Dredging process is a blended essence of following three independent elements: excavation, transportation of excavated material and then usage or proper disposal of dredged material.
History of dredging
With the beginning of civilization, there started the transportation of commodities by inland waterways and oceans. But this transportation depended on the ability of ships, which in turn largely depends on the water depth. Silting, the natural phenomenon of deposition of silt and sediments over the sea bed created a constant threat to the voyages of ships. People started fighting with the problem of siltation to ensure the safety of voyages but due to lack in equipment for removing siltation, they started manual digging up of the mud by hand which was not that efficient and limited to shallow waterways.
In 15th Century increase in trade at seas necessitated the development of some bed scratcher such as “Zeeuwse Krabbelaar”, which was a primitive bed leveller. These bed levellers cum scratchers were used to pick the sediments and dispose them. Development in these dredgers was carried out in certain phrases starting from ancient mills to modern suction dredgers.
Mills were developed around 1575, these were a sort of dredging equipment which was primarily employed for digging in ports. Mills had a rotating chain connected with wooden boards, these wooden boards dig up the mud.
At the primary stage of development of mills they were manually driven later they were powered by steam engines. Mills had gone obsolete in 1857 with the development of a suction dredger in the United States.
In 1867 there came a revolutionary development with the evolution of the design of suction dredger by a French engineer. He used successfully this suction dredger in dredging the Suez Canal. From then on, dredging by suction became more and more common.
There came cutter suction dredger and trailing suction hopper dredgers in the 19th century. These are the modern dredgers and can avail efficient dredging. These were so efficient that they allowed shipping and dredging simultaneously without hindering the traffic.
Recent evolutions in dredging have optimization of dredging process on its main focus rather than developing new dredgers. So standardization of dredgers and equipment, and advancement in control and monitoring systems of dredgers improved dredging to a great extent.
Importance of Dredging
Dredging is an activity of huge importance in the maritime industry. It serves the following purposes:
- It helps in safer voyages by pacifying underwater traffic and by maintaining proper bottom clearance
- In some cases, dredging is indeed employed for the extraction of ocean gems such as shellfish and molluscs. So, dredging can help in exploring amazing varieties of these creatures.
- To channelize the construction of a network of bridges, dams or other civil engineering works in water, dredging is a primary requirement. These are only proper dredging tools which remove the requisite amount of underwater silt and other compositions and make the excellent constructions true that a civil engineer wonders
- Dredging is also important to make the marine eco-system pollution-free. It helps in eco-friendly disposal of deposited polluting toxicants and harmful materials, without causing any harm to the marine ecosystem.
- Dredging helps not only in preserving flora and fauna in water bodies but also used for recreational activities.
Effects of Dredging
But just like every coin has two sides, even dredging, in spite of all the positive attributes to the process, has negative points. These negative points are also important because they also tend to impact the existence and life of the marine habitat at large.
These negative effects of dredging are briefed as under:
- When dredging is carried out for marine engineering purpose or constructional work, a large amount of water is to be removed and stored at some other location. This creates a minor storage problem but extensively affects the life of flora and fauna prevalent in that water. This is due to change in mineral composition of water before and after both dredging and depositing it back in its source after construction.
- Dredging impacts the crops badly in the regions where it is carried out to de-silt the rivers which are primarily intended to quench the irrigation demand of the region. Because along with silt essential minerals also get dredged out leaving the resultant water and land lacking in nitrates and phosphates.
- Also if dredging is carried out to serve the cleaning purpose, the toxic waste to be removed alarms the safe disposal problem. If it is disposed on land to make the land barren and if in other less important water body harms the living creatures in that water body.
These ill-effects of dredging becomes insignificant in comparison to applications and importance of dredging but should be kept in mind and catered where necessary.
Dredging Industry has developed itself throughout the world in the last two decades.
It serves multi-purposes such as cleaning, maintenance, disposal, transportation, excavation, etc. at a time.
Dredging helps in making the water navigable and makes fishing easier even in shallow creeks. It helps in removing contaminants from the waterways and recreating damaged areas by reclamation works.
But an important aspect which we have to cater while dredging is safe dumping of material to be dredged. It should be disposed-off at a place where no significant landform and life-form get harmed. Also at some places dredging alters the mineral composition of the water; precautions should be taken, so as to oversee the alterations caused by the change in mineral composition.
By putting small things in place we can prevent the occurrence of a major catastrophe. Today with the advancement in dredging technology we have pushed dredging towards higher efficiency with lower environmental impact.
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