Downstream Sediment Management by Dredging

Sediments, as one of the important elements in the geological dynamics of the earth, are materials that accumulate from the weathering of decomposed rocks and marine organisms. In a geological context, sediment involves small particles that can settle and accumulate in various environments. Sediment is not limited to soil and rocks, but also involves particles that can be carried by water, wind or ice. Sedimentation itself is the result of the separation and accumulation of sediment particles in certain places. The process of sedimentation occurs, caused by river water, ocean waves, and wind which are the main transportation to move sediment particles from one place to another, then deposit them on the bottom of the waters or on the surface of the land. This process can form various morphological forms such as river deltas, swamps, or even sedimentary rocks downstream from a body of water. The impact of sediment deposition downstream can cause several problems such as siltation of the waterway and changes in topography, which can lead to changes in shipping routes. Loss of habitat and biodiversity of coastal areas such as coral reefs, this is due to the lack of light entering the waters so that the photosynthesis process of corals will be disrupted. Increased disaster risk, sediment buildup can increase the risk of disasters such as flooding, especially if the sediment blocks the flow of rivers or estuaries. And can cause chemical contamination, sediments can contain chemicals such as heavy metals, pesticides, and other industrial chemicals that can pollute coastal ecosystems.

To overcome the sediment buildup that occurs in the downstream area, sediment dredging is required. Sediment dredging is the process by which contaminated or accumulated sediments underwater are removed, treated, and/or placed in a new location. Sediment dredging is conducted to reduce the risks posed by sediment buildup.

One of the marine instrumentation used for dredging sediment, mud, or material from the bottom of waters including sea areas is a dredger. A dredger is a specialized type of vessel designed to perform dredging work or excavate material from the bottom of waters such as rivers, harbors, and seas. The main purpose of using a dredger is to increase water depth, remove excessive sedimentation, or move materials such as mud, sand, or gravel. Dredgers play an important role in civil engineering projects, port construction, coastal development, and shipping line maintenance. Using specialized equipment and material storage systems, dredgers can transport and dispose of sediment to designated disposal sites. This process helps maintain the required water depth for large vessels and reduces the risk of sedimentation that can impede navigation. The following are the types of dredgers that are commonly used:

Cutter Suction Dredger (CSD) is a type of dredger equipped with a cutter at the end of the suction pipe. This cutter cuts and crushes the sediment before it is sucked up and moved through the pipe to the disposal site.
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Trailing Suction Hopper Dredger (TSHD), uses a funnel (trailing suction hopper) to suck sediment into a storage space called a “hopper.” Once the hopper is full, the vessel sails to the disposal site and removes the sediment.
Bucket Dredger, using a bucket attached to a chain or rotating wheel to excavate and transport sediment from the seabed. The bucket is then lifted and dumped into a disposal site.
Grab Dredger, using a hoe (grab) that opens and closes to extract sediment from the seafloor. Sediment collected in the grab is removed and disposed of.
Backhoe Dredger, is a type of dredger equipped with a backhoe similar to a land-based machine. This digging machine is used to extract sediment and other materials from the seabed.
Water Injection Dredger, uses a high-pressure stream of water to disrupt and transport sediment from the seafloor. Water sprayed through a pipe or nozzle helps break up the sediment before it is transported.
Auger Dredger, uses a rotating screw (auger) to excavate and transport sediment from the seabed. The sediment is then transported via conveyor to a disposal site.
Air-lift Dredger, uses compressed air to lift sediment from the seabed to the surface. Air is supplied through pipes to create lift flow.

How Dredger Work​

The following are the workings or basic operating principles of dredgers in general regardless of type or type:
1. Cutting or Excavation, In many types of dredgers, the first step is to cut or excavate sediment or material from the seabed. This can be done using a cutter, bucket, grab, or other excavation tool attached to the vessel.
2. Suction, Once the material is produced from the cutting or excavation process, the next step is to suction or suck the material. Dredgers are generally equipped with a suction system that uses a pump to create negative pressure in the suction pipe. This system allows material to be sucked into the suction pipe from the working area on the seabed.
3. Material Transfer, Material that has been sucked by the suction pipe is then transferred to the appropriate part of the ship, such as the hopper on the Trailing Suction Hopper Dredger (TSHD) or the storage tank on the Cutter Suction Dredger (CSD).
4. Material Disposal or Storage, Material collected in hoppers or storage tanks can be disposed of at designated disposal sites, or, in some cases, can be used for construction or land filling purposes. Some dredgers are equipped with additional conveyor systems, pipes, or pumps to move the material to its destination.
5. Monitoring and Control, In its operation, the dredger is equipped with monitoring and control systems to ensure operations run efficiently and safely. The dredger operator monitors operational conditions, speed, and volume of material being transported to optimize performance and minimize risks.

Dregder Strengths and Weaknesses​

Strenght :
  1. Increasing Water Depth, Dredgers can be used to increase water depth in harbors, rivers, and other navigation areas, allowing large vessels to sail unimpeded.
  2. Harbor Cleaning and Maintenance, Dredgers are effective in removing sedimentation material, silt and gravel from harbor areas, maintaining the accessibility and performance of maritime infrastructure.
  3. Land Reclamation, Dredgers can be used to collect sedimentary material and create new land, which can be utilized for the construction of residential or industrial projects.
  4. Fast and Efficient Dredging, Dredgers can perform dredging quickly and efficiently, enabling more economical maintenance and development of maritime infrastructure.
  5. Flexible Material Handling, Dredgers can handle various types of sedimentary materials, including mud, sand, gravel and other materials.
Weakness :
  1. Environmental Impacts, The use of dredgers can have negative impacts on the environment, including water pollution, marine habitat loss, and changes to river or coastal flow characteristics.
  2. Marine Habitat Loss, Dredging operations can cause habitat loss for marine organisms, especially for species that depend on a stable marine substrate.
  3. Operational and Maintenance Costs, Dredgers require significant operational costs, including fuel costs and routine maintenance, which need to be factored into project planning.
  4. Use of Water Resources, Dredging can lead to poor water circulation and quality, especially if not done carefully and in accordance with environmental regulations.
Writer : Galuh Pramudya

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