doubledredging

Doubledredging is a dredging technique in which two consecutive dredging passes are made over the same site within a short time frame to increase excavation depth or improve sediment removal efficiency. The term is used in some civil engineering and port maintenance contexts, but it is not universally standardized and may be described differently by contractors.

In practice, the first pass loosens and mobilizes sediment; the second pass removes the loosened material more completely or targets finer sediments and contaminated layers. It is commonly employed for harbor channels, approach channels, or river sections that require precise depth targets beyond what a single pass can achieve.

Equipment commonly involved includes cutter suction dredges and trailing suction hopper dredgers. Double-pass sequencing can be integrated with real-time depth monitoring and contour control, with dredge timing adjusted for tides and weather to limit sediment plumes and manage disposal or dewatering requirements.

Environmental considerations include turbidity and resuspension of sediments, potential release of contaminants, and habitat disturbance. Mitigation measures include scheduling dredging during favorable conditions, using silt curtains or containment, and implementing sediment dewatering or onshore treatment when feasible. Regulatory approval typically requires an environmental impact assessment and ongoing monitoring.

Advantages of doubledredging include faster achievement of target depths and more complete removal of compacted or difficult sediments. Disadvantages include higher capital and operating costs, greater energy use, and increased temporary environmental disturbance.