The use of waterways such as rivers and lakes has been a go-to for individuals and companies that need to transport goods a long distance. Dredging is used to keep moving sediment and sand clear from waterways in order to allow vessels to move freely through.
Let’s take a deeper look into dredging, why and how it’s done, and how it impacts the environment.
What is Dredging?
Dredging is the process of removing sediment, plant material, and/ or rock from the beds of waterways such as rivers, lakes, and canals with a dredge.
Some commonly dredged material includes:
Coastal dredging is also a popular routine of coastal and marine infrastructure developments.
There are two main types of dredging:
- Maintenance dredging: Opens up new marine areas for development
- Capital dredging: Used to maintain previously dredged areas
Why is Dredging Important?
Dredging is an extremely important process in the maritime industry and, in many cases, is seen as a necessary process.
Some of the reasons dredging is needed includes, but is not limited to:
- Ensuring the safety of voyages by reducing underwater obstetrical and maintaining good bottom clearance
- Increasing the depth of navigation channels, thus allowing marine traffic to flow smoothly
- Creating space for construction or digging foundations for bridges, dams, and various civil waterworks
- Removing toxic waste from marine environments
How Does Dredging Work?
In the process of dredging, a dredge (a large flat marine vessel) is used to either scoop, drag, or pump up muck and mud from water bodies.
The persons operating the dredge will lower a rotating head which is used to loosen up debris on the water body floor. While this is happening, a pump is used to suck up the material and place it on the dredge.
The removed sand and sediment are then transported to a location for their final processing.
What Is Done With Dredged Material?
The final location of the removed sediment depends on location, the operations of the surrounding area, and local laws and regulations.
In some coastal areas, sand dredged from the coastline is used to rebuild, widen, and restore beaches (beach nourishment) that have begun to wash away due to erosion.
If the sediment is deemed non-toxic and there is no alternative use for it, some dredging companies will drop their loads far out at sea.
Some dredged material is used for construction purposes, especially when the dredging is done to create space for development. Although not all sediment can be used, some may be helpful for changing landscapes and building foundations.
When there is no alternative use for the dredged soil, and if the ocean is too far/ the material is deemed unsafe for ocean disposal, the sediment is brought to a confined disposal facility, which is enclosed to prevent the sediment from returning to the environment.
That said, environmentalists are constantly looking for new ways to reuse this dredged material in a more sustainable fashion. Some of these include:
- Used to restore Superfund sites
- Used to restore Brownfield sites
- Construction material (such as building roads)
- Restoration of green space habitats
The Environmental Impacts of Dredging
Although dredging is seen as a necessary process, both for safety and functionality in our society, it does not come without its risks. In fact, dredging has been seen to have a major negative impact on the surrounding environment.
As sediment is mixed up during the process, fish breeding grounds are destroyed, river banks can become unsettled, and settling silt can suffocate plants by reducing oxygen and sunlight levels.
The sediment that is disturbed from dredging is often light and drifts easily downstream, leaving the environmental impacts out of sight of the dredging area, which has in the past left the ecological impacts of the process unchecked.
A study published in the ICES Journal of Marine Science suggests that dredging has an array of negative effects on marine animals, as well as those that live close to water bodies.
According to the study, some direct impacts include:
- Collisions: Animals such as otters, alligators, whales, and fish often collide with dredges, or their propellers
- High Noise Levels: Mammals that rely on sound for hunting are greatly affected by the noisy process of dredging. This sound also disrupts communication and can chase away prey from otherwise abundant areas
- Sediment Plumes: Increased turbidity in the water can create sediment plumes that can travel great distances downstream, thus expanding the area of impact by a significant amount
Furthermore, habitat destruction and potential toxic sediment spread threaten not only the environment of plants and marine animals but that of humans too.
The Positive Environmental Impacts of Dredging
Although dredging is seen, for the most part, as a negative environmental practice, some possible positives could arise from the activity.
The disturbance of sediment has been seen to enhance the diversity and abundance of fauna near dredged areas. This could be due to nutrients being released from sediment plumes.
Changes in topography can aid some animals. Bottlenose dolphins have been known to prefer hunting in previously dredged areas as it aids with prey detection and capture.
Increased food availability due to the waterbody floor disturbance can increase food supply, which in turn aids in growth and population spread; however, this is usually short-lived and followed by a drastic decrease in food availability and diversity.
Environmentally Friendly Alternatives to Dredging
Traditional dredging has massive impacts on the environment, not only in the immediate area but in many surrounding habitats. Not to mention it’s incredibly expensive and often leaves a lot of waste products.
Luckily, environmentalists have been working on ways to conserve the ocean and water bodies.
One environmentally conscious alternative to this is biological dredging.
Although the removal of rocks and large sediments still needs to be done by machine, bio-scientists have discovered a means of introducing bacteria into water bodies that accelerate the decomposition of plant material and remove excess nutrients from the water.
This process has simply found a way to redirect the excess nutrients and sediment back into the natural ecological flow.
Bio-dredging is both cheaper and has less of an impact on the environment.
What are the biggest dredging challenges?
There are three major challenges that are linked to dredging, including disturbance of contaminated material, increased turbidity, and material disposal.
Does dredging improve water quality?
Dredging can, in some cases, improve water quality by removing excess vegetation, trash, sewage, and other debris. That said, dredging projects carried out to deepen channels often decrease the quality of the water.
How deep can a dredge go?
The depth that can be dredged will depend on the machinery that is being used. Smaller dredges can be used in less than 2 meters of water, while some of the largest dredging machines can reach dredging depths of up to 35 meters.