Dredging is the process of excavating and removing silt deposits accumulated in water bodies. This process is meant to deepen or clean the waterways to ensure smooth and safe navigation, to pre-treat space to construct bridges and dams and to sieve the water of its material deposits. The excavation process involves the removal of both natural and manmade sediments from waterbeds.
Dredging is of utmost importance to maritime activities as it ensures a safe voyage by maintaining proper bottom clearance. By removing and disposing of material deposits and sediments from underwater, dredging ensures pre-treated grounds for engineers to work on in the construction of dams and bridges. Dredging plays a vital role in keeping the marine ecosystem pollution-free by removing pollutants and toxicants from water. Not only does dredging help with keeping the marine ecosystem alive but it helps reclaim the damaged lands using beach refilling or other land reclamation methods.
The history of dredging dates back to as early as the 15th century. As the waterways were bustling with trade ships, the growing business world demanded safer and faster routes and primitive bed levellers and scratchers like “Zeeuwse Krabbelaar”, were put to use. Their limitations were overcome by modifying them to reach the modern-day suction dredges. Having come so far, the evolution of dredging now focuses more on optimization of the dredging process rather than developing new dredges.
Based on the disposal of debris dredging can be classified into two, mechanical and hydraulic. Mechanical dredging makes use of tools like buckets and grabs for sediment excavation. Mostly used for sediment extraction from shoreline and land, mechanical dredges can operate from offshore as well with the assistance of barges. Hydraulic dredging makes use of pumps to transport sediments from the water to the disposal location.
Though mechanical dredgers can dredge hard compacted sediments, the quantity of sediment is limited to one scoop and hence it is a time-consuming process. Unlike mechanical dredges, hydraulic dredges mostly use centrifugal pumps to suck out sediments. Hydraulic dredges are more cost-effective when compared to mechanical ones as they demand less equipment and transportation of sediments to the shoreline is directly through the pumps cutting the cost of transportation barges. Energy used and emission is also comparatively lesser for hydraulic dredges.
Bucket dredgers, Grab type dredgers and backhoe dredgers are some of the commonly used mechanical dredgers. Bucket dredgers are stationary dredgers that rotate in an arc and their scraping end is fitted with a bucket that scrapes the debris out. The bucket is tilted upside down to dispose of the debris. Grab type dredgers are also stationary and they have a grab shaped like a clamshell as their dredging tool. Backhoe dredgers, mainly used in shallow waters, work near the banks or on barges. It has a fixed length hydraulic arm as its dredging tool.
Suction dredgers, cutter suction dredgers, trailing suction hoppers, and reclamation dredgers are the types of hydraulic dredgers in common use today. Suction dredgers, mainly used for sand mining, suck out sand from the mines and the excavated material is brought with the help of water jets. Cutter suction dredges are used to loosen the base that is to be dredged. Trailing Suction Hopper Dredger comes with a hold or hopper adjustment to collect the excavated material. A reclamation dredger cannot be called a dredger on its own but rather assisting equipment in dredging operations.
Dredging helps to ensure safer transportation over the waterways and maintain the depths of ports and harbours. Dredging is vital to beach renourishment, which is a sustainable solution to soil erosion in coastal areas. But dredging also comes with its fair share of ramifications. Displacement of huge quantities of sand from water bodies as part of the dredging process and the chemical imbalance caused so can adversely impact aquatic life. Often the disposal of toxicants and pollutants removed from dredging sites is a matter of concern. When disposed on land, it barrens the land and if deposited elsewhere in the waters, it harms the living creatures in the water bodies. Dredging hurts the crops of the region as well, as it removes essential minerals along with silt from rivers.
The dredging industry has seen tremendous growth in the last two decades. It is a sustainable solution for riverbeds cleaning, channel maintenance, etc. It is vital to safe navigation and fishing, which serves as a livelihood means for many across the globe. It also removes contaminants from water bodies and helps reclaim damaged and lost land due to climate changes. When the disposal of debris is carried out without harming the natural resources and dedicated studies conducted on the aftermath of dredging to suggest solutions for the changes in mineral composition, dredging can go a long way ahead in preventing major catastrophes.
