Sediment Removal 101: What Is Dredging?
Dredging is a process used to remove accumulated sediment from the bottom, and in some cases, the banks or sides of a river, lake, stream or other body of water. A specialized piece of equipment called a dredge creates a vacuum that sucks up and pumps out the unwanted sediment and debris.
You may have heard of a naturally occurring process called sedimentation, which is the accumulation of silt, sand and other debris on the bottom of a river, lake, canal or stream over time. An excessive build-up of sediment can cause a series of issues. For instance, it can reduce the depth of the waterway and prevent the passage of ships. It can also lead to contamination that poses a threat to aquatic plant and wildlife. In coastal areas, sediment accumulation can cause beaches to erode.
We depend on waterways such as rivers, lakes, harbors and bays for everything from transporting goods to commercial fishing and recreation. Over time, these waterways can become filled with sand, silt and debris — or sediment — that make them difficult to navigate and sometimes pose an environmental hazard.
It often becomes necessary to find a way to remove a large accumulation of sediment to preserve the health of the waterway and enable its continued use for commercial applications. A process known as dredging can provide a fast, efficient sediment removal solution. There are various types of dredges that can be used for the sediment removal process.
The sediment removal process uses a machine known as a dredge to excavate the accumulated sediment and debris. A dredge is either partially or completely submerged in water and allows the operator to easily gather the sediment and transport it to a different location. When dredging is done, sediment is relocated to a new location and used for a number of purposes.
Watch a Dredge in Action:
What Is Dredging Used For?
Sediment removal, or dredging, is used for a number of purposes. Below are the applications that one would use dredging for:
- Waterway Maintenance: Dredging is an important waterway maintenance step, which is probably its most important application. By removing the accumulated debris, dredging can restore the waterway to its original depth and condition. Dredging also removes dead vegetation, pollutants, and trash that have gathered in these areas.
- Create waterways: Many ports are building new waterways with dredging to reach new trade centers and improve the efficiency of the transport of goods. Dredging ensures cargo vessels of all sizes can dock and do not run aground.
- Excavation: Sediment removal plays an important role in the preparation for construction projects such as bridges, docks and piers by performing the necessary underwater excavation work.
- Reclamation: Dredging can remove contaminants that occur due to chemical spills, sewage accumulation, buildup of decayed plant life and storm water runoff.
- Increasing Waterway Depth: As sediment builds up on the bottom of the waterway, it reduces the depth of the water. Dredging strips away the accumulated debris, which can restore the water body to its original depth and reduce the risk of flooding.
- Wildlife Preservation and ecosystem maintenance: Dredging helps ecosystems in a variety of ways. By removing trash, sludge, dead vegetation and other debris, it keeps the water clean and preserves the local wildlife’s ecosystems. It also remediates eutrophication, which is an excess of nutrients in the water due to runoff. By solving eutrophication, you stop the excess growth of plant life, which can cause oxygen deprivation.
- Reconfiguring for Larger Ships: By deepening and widening a waterway, dredging can make it passable for larger cargo vessels, which can have a positive economic impact.
- Shore Replenishment: Storms, offshore mining, natural disasters, like hurricanes, and human-made disasters can cause a beachfront to erode over time. Dredging can help to restore the beachfront to its original condition. Beachfront areas often erode which can change their landscape and impact the local ecosystem. Dredging reverses the effects of soil erosion, keeping the local ecosystem and its native plant and aquatic wildlife intact.
- Gathering Construction Materials: The sediment removal process is sometimes used to gather sand, gravel and other debris used to make concrete for construction projects.
- Trash Removal: Dredging can assist in keeping waterways clean by removing trash and debris from beneath the surface.
- Mining for Precious Metals: In certain bodies of water, the sediment can contain traces of precious metals such as gold and diamonds. Dredging can aid in excavating this mineral-filled sediment.
- Pond and Lagoon Cleaning: As ponds and lagoons contain stagnant water, they often can become mucky and have a foul odor. By using dredging, one can remove the accumulated sediment that has caused this making for a healthier body of water.
What are the Benefits of Dredging?
Dredging provides numerous benefits for shipping, construction, and other projects. The advantages of dredging are:
- Widening and Deepening: Dredging can be a critical process for the commercial shipping industry. Removing sediment can maintain the appropriate width and depth for enabling the safe, unobstructed passage of cargo vessels carrying oil, raw materials, and other essential commodities.
- Waterway Project Preparation: Dredging is a critical underwater excavation step in many waterway construction projects such as bridges, docks, piers and underwater tunnels.
- Land Reclamation Projects: Sediment removal is sometimes used as a source of materials for land-building projects. The liberated sediment can then be dried out and transported to a new location where additional land is required for building and other purposes.
Dredging also has numerous environmental benefits, including:
- Environmental Remediation: Sediment removal can help to restore a shoreline or beachfront to its original condition by reversing the effects of soil erosion.
- Cleanup Applications: Dredging can clean up a waterway after a toxic material spill or via the removal of trash, debris, decaying vegetation, sludge or other materials that can contaminate water and soil.
- Preserving Aquatic Life: Dredging can produce a healthier aquatic eco-system that can result in a more suitable habitat for fish and other wildlife. It can also be used for trash and debris removal to keep the waterways clean.
- General Pollutant Removal: Water bodies located near urban areas and industrial complexes can quickly become a receptacle for various pollutants. Sediment removal can prevent the accumulation of pollutants and keep the waterway clean and healthy.
- Remediation of Eutrophied Water Bodies: Eutrophication is an excessive amount of nutrients in a water body typically caused by water runoff from the surrounding land. Eutrophication can lead to an overabundance of plant growth that results in oxygen deprivation and can cause the death of aquatic wildlife. In some cases, dredging may be the most viable remediation option when eutrophication occurs.
The Sediment Removal Process: How Dredging Works
How does dredging work? A dredge, the machine used to execute the sediment removal process, is equipped with a powerful submersible pump that relies on suction to excavate the debris. A long tube carries the sediment from the bottom to the surface. The disposal of the dredged material must be conducted in compliance with federal, state and local government laws and regulations.
When dredging, the operator lowers the boom of a dredge to the bottom (or side) of the body of water. A rotating cutter-bar then uses teeth to loosen the settled material, as the submersible pump removes the sediment from the bottom of the waterway. The silt and debris are then transported away for final processing. Check out the infographic below to learn how the dredging process works!
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What are the Different Types of Dredges?
There are several types of dredges used in the sediment removal process. The most common types of dredges are:
- Plain-Suction: A plain-suction dredge is the most common type of sediment removal equipment. Unlike other dredge versions, it doesn’t contain a tool for penetrating or cutting into the bottom of the water body — it relies on suction to remove loose debris.
- Cutter-Suction: This type of dredge contains a cutting tool that loosens material from the bottom and transports it to the mouth of the suction apparatus. The use of a cutter-suction dredge may be necessary for removing debris from hard surfaces that would prevent efficient suction via standard methods.
- Auger-Suction: An auger-suction dredge essentially bores holes into the bed to loosen and suck up the debris. The rotating auger can burrow deeply into the surface. This type of dredge works well for sludge removal applications at wastewater treatment plants and other areas requiring heavy-duty sediment removal.
- Jet-Lift: This technologically advanced sediment removal equipment works by injecting a high-volume stream of water to pull in nearby water, silt, and debris.
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*Last Updated 4/25/2019