Dredgers are classified according to their operating principle. Suction dredgers draw material through a large pipe using centrifugal pumps; cutter‑suction dredgers combine a rotating cutter head with suction, allowing the machine to break up harder soils before removal. Mechanical dredgers use buckets, grabs, or chain‑ladder buckets that physically scoop material, while trailing suction hopper dredgers tow a suction pipe along the seabed and store the excavated material in an onboard hopper for later disposal or transport. Bucket‑wheel dredgers feature a rotating wheel fitted with buckets, providing a continuous flow of material for large‑scale operations.
The primary functions of a dredger include maintaining and deepening navigation channels, replenishing beaches and coastal defenses, extracting sand and gravel for construction, and restoring aquatic habitats by removing contaminated sediments. In addition, dredgers are employed in mining operations, such as extracting tin or gold from riverbeds, and in flood‑control projects where sediment buildup reduces water‑flow capacity.
Historically, dredging began with manual tools and simple wooden barges, but the Industrial Revolution introduced steam‑powered and later diesel‑driven machines, dramatically increasing efficiency and scale. Notable early examples include the dredgers used to deepen the Suez Canal in the 19th century and the extensive fleet employed during the construction of the Saint‑Lawrence Seaway in the 20th century.
Modern dredging must address environmental concerns, as the process can increase water turbidity, disturb benthic ecosystems, and mobilise pollutants. Regulatory frameworks typically require impact assessments, sediment containment, and the implementation of mitigation measures such as silt curtains, sediment traps, and careful timing of operations to protect fish spawning seasons.