What is dredging?
Dredging refers to the practice of removing or excavating materials from the seabed or the bottom of waterways, most commonly in shipping channels, ports, rivers and lakes.
The process involves removing the material, such as sand, rock, clay or silt, transporting the dredged material, and safety unloading it at an approved disposal site.
There are two common reasons for dredging:
- Maintenance dredging - performed to ensure that shipping channels, berths and harbours remain a certain depth to allow ships to pass through wihtout running aground.
- Capital dredging - new work carried out to create new shipping channels or deepen existing berths to enable larger ships and vessels to utilise the waterway.
How is dredging performed?
There are two ways that dredging can be performed:
- Marine-based dredging - performed from the water, usually using an excavator referred to as a backhoe dredge, which is mounted on a floating barge and manoeuvred by tug boats.
- Land-based dredging - best suited for excavating small volumes of material that are close to the shore or harbour. This might be appropriate for maintenance or capital dredging works involving new or existing berths (where vessels dock to be loaded or unloaded), as the activities are adjacent to the land allowing use of land-based machinery such as large, long-reach excavators.
It there is a lot of rock in the excavation zone, sometimes additional equipment, such as drum-cutters or underwater rock hammers, are used to break-up the rock so the excavator can remove it.
Is dredging regulated?
Dredging is regulated and cannot be carried out unless the activities comply with relevant local, state and federal legislation. Various environmental and planning laws and policies apply to dredging to mitigate disturbance to marine habitat and organisms, and manage dredge material disposal activities.
During the initial planning stage of any capital or maintenance dredging program, the TACC will be involved in preliminary assessments process to help determine what legislation and policies apply, and ensure all requirements are satisfied according to best practice standards.