This environmental dredging is often necessary because sediments in and around cities and industrial areas are frequently contaminated with a variety of pollutants.
These pollutants are introduced to waterways from point sources such as sewer overflows, municipal and industrial discharges, and spills; or may be introduced from nonpoint sources such as surface runoff and atmospheric deposition.
NOAA's Office of Response and Restoration plays a major role in protecting and restoring marine natural resources when environmental damage occurs. The disposal of dredged material is managed and carried out by federal, state, and local governments, as well as by private entities such as port authorities. The U. Army Corps of Engineers issues permits for the disposal of dredged material; the U. The oldest known dredging activities are: dredging for peat excavation and maintenance dredging.
Maintenance Dredging is a broader term that 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 that 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 dredgers is used to remove the deposited sediments from an inlet creek, waterway or ocean floor. The dredging process is a blended essence of the following three independent elements: excavation, transportation of excavated material and then usage or proper disposal of dredged material. 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 of equipment for removing siltation, they started manual digging up of the mud by hand which was not that efficient and limited to shallow waterways.
These bed levellers cum scratchers were used to pick the sediments and dispose of them. Development in these dredgers was carried out in certain phrases starting from ancient mills to modern suction dredgers.
Mills were developed around , these were a sort of dredging equipment that 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 the development of mills they were manually driven later they were powered by steam engines.
Mills had gone obsolete in with the development of a suction dredger in the United States. In 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. Then came cutter suction dredgers and trailing suction hopper dredgers in the 19 th century.
These are 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 the optimisation of the dredging process as its main focus rather than developing new dredgers.
So standardizations of dredgers and equipment, and advancement in control and monitoring systems of dredgers improved dredging to a great extent.
Dredging is an activity of huge importance in the maritime industry. It serves the following purposes:. The dredging process is a combination of digging the soil in the water bed and removing or extracting that soil from the excavated surface.
Hence, the types of dredging methods can be classified into three categories depending upon how the debris is extracted from the site.
Mechanical dredging is the process in which the sediments are picked up using mechanical tools such as buckets, grabs etc. Mechanical dredging is usually carried out near the shoreline.
Hence for removing sediment on land or shoreline, mechanical dredging is used. The dredged sediment is picked up and placed in nearby land or in water or most of the time in another barge dedicated to carrying the sediment. If the dredging is done near the shoreline, the sediment can be directly transferred to a truck or railway wagon.
If the mechanical dredger is an onshore dredger it has a limitation of covering the area as it can only be used near the shoreline. With barge type mechanical dredgers it can be operated in any water, however, it will be most effective near docks, piers etc. The mechanical dredging can be a continuous process, however, the quantity of the sediment will be limited to one scoop which is lifted every time to remove the sediment. The mechanical type is able to dredge hard compacted sediments and water carryover is way less than hydraulic dredging.
In the hydraulic dredging process, the sediment is removed from the dredged site by using pumps, usually, centrifugal pumps are sucked into the pipe used to transport the sediment. The sediment is mixed with water and made into a slurry mixture which makes it easier for the pump to transfer it.
Depending on the pumping distance, a booster pump can be fitted inline to transfer the sediment to the nearest shore to maintain a constant production rate. One of the major advantages of the hydraulic dredging process is the elimination of additional transport medium or equipment as the sediments can be directly transported to the shore facility, saving additional expenditure and time.
The method of hydrodynamic dredging is normally used for maintenance of channel, port , harbour depths etc. Once the area is dredged, it needs to be constantly maintained to avoid unsafe navigation by maintaining the required depths. This method utilises water injection technology, which injects large amounts of water using nozzles attached to a horizontal jet bar powered by pressurised pumps.
As the water spray from the nozzle hits the water bed, it fluidizes the sediments, making them loose. NQBP claims the science is on its side and that there is no unequivocal evidence that dredging, when conducted properly, is harmful to marine environments.
In August, the previous Labor government released a report it commissioned stating that spoil from dredging travels a lot further than previously thought, with dumped sediment capable of being disturbed repeatedly by severe weather. However, the analysis doesn't rule out dumping dredged waste at sea and suggests various locations near existing ports that would do the least damage to coral and other marine wildlife.
However, recent research by James Cook University found it was likely that dredge spoil is more harmful to marine ecosystems than sediment washed into the sea by rivers. This article is more than 7 years old. This widely used practice is essential for maintaining harbours and shipping routes, but what are the risks?
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