About Dredging

Building and Maintaining America’s Waterways

Dredging is the process of removing sediment from the bottom of rivers, harbors, lakes, and coastal channels to maintain safe and efficient navigation. It plays a critical role in supporting commerce, national security, coastal resilience, and environmental restoration. From deepening shipping channels for larger vessels to restoring beaches and wetlands, dredging helps keep waterways open, communities protected, and maritime infrastructure functioning.

Using specialized equipment designed for different environments and materials, dredging operations carefully balance engineering needs with environmental stewardship—ensuring that America’s waterways remain safe, reliable, and sustainable for generations to come.

What is Dredging?

Dredging is the process of excavating and removing sediment—such as sand, silt, clay, or rock—from the bottom of waterways. Over time, natural forces like currents, tides, storms, and river flow cause sediment to accumulate in navigation channels and harbors. Without periodic removal, this buildup can reduce water depth, restrict vessel traffic, and impact flood control and drainage systems. Dredging restores and maintains the depth and capacity of these waterways, ensuring they remain safe and functional.

There are several types of dredging methods, generally grouped into hydraulic and mechanical approaches. Hydraulic dredges use suction to remove sediment in a slurry form and transport it through pipelines or into onboard storage. Mechanical dredges use buckets or clamshells to physically lift material from the bottom. The method selected depends on factors such as material type, water depth, environmental conditions, project size, and placement requirements.

Beyond navigation, dredging serves many additional purposes. It supports beach nourishment and shoreline protection, helps restore wetlands and aquatic habitats, deepens ports to accommodate larger vessels, and assists with environmental remediation by removing contaminated sediments. Modern dredging operations rely on precise positioning systems, environmental monitoring, and engineered placement strategies to balance infrastructure needs with responsible environmental stewardship.

In short, dredging is both an engineering activity and a long-term investment in maintaining safe waterways, protecting coastal communities, and supporting economic activity tied to maritime transportation.

Types of Dredges

Hydraulic Dredging

Hydraulic dredges use water pressure and suction to excavate and transport sediment through pipelines or into hoppers. They are the most common type of dredge used for large-scale marine and inland dredging projects.

Mechanical Dredging

Mechanical dredges use physical excavation methods such as buckets or clamshells to remove material from the waterbed. They are particularly effective in hard or compacted soils and for precision dredging work.

Choosing a Dredge

Dredging efforts are supported by auxiliary equipment including pipes, boosters, and scows to move sediment and other support vessels. The type of dredge used for a project is based on the needs of the project and the pros and cons of each type of dredge. A few of the considerations are summarized below.

Sketch of hopper, cutterhead and mechanical dredges at work, with bed leveling and water injection

How hopper, pipeline cutterhead and mechanical dredges compare
Aspect	Hopper	Pipeline Cutterhead	Mechanical
Intent	Designed for large navigation channel dredging. Most efficient in coastal environments to remove large volumes of material.	Most efficient in riverine environments protected from extreme sea states with close placement options.	Traditionally used in small, discrete locations (e.g., docks, seawalls, marinas). Can be used in riverine environments.
Limitation	Dredging is not continuous due to having to offload material when hopper is full. Requires transit to and from placement sites.	Cannot operate in rough seas. Lost dredging time when moving out of the way of shipping vessels.	Limited ability to work in rough seas. Slowest dredging method.
Maneuverability	High - Self-propelled, ability to navigate around commercial shipping traffic.	Low - Stationary barge-mounted. Moves by repositioning (walking) the spuds forward to the next location.	Low - Stationary barge-mounted.
Dredge Material	Coarse grain sand to fine grain silt.	All forms of sediment ranging from intact rock to silts.	All forms of sediment ranging from fractured rock to silts.
Availability	Less than 20 dredges shared nationally.	Lots of availability, may be limited by size needed.	Lots of availability, may be limited by size needed.
Entrainment/ Entrapment Risk	Highest entrainment risk, limited to the path of the draghead. Approximately 70% of hopper dredging projects do not result in take.	Low entrainment risk, limited to small area where the cutterhead is swung back and forth. Very few takes ever recorded.	Very low risk. Limited to entrapment from the dredge bucket lowered into the water. Very few takes ever recorded.

Engineering Manual on dredging and dredged material management