Cofferdam

A cofferdam is a temporary, watertight enclosure built within, or across, a body of water to allow construction, repair, or inspection work in a dry area. By isolating a section of the watercourse or shore and removing the water from inside the enclosure, workers can access the worksite as if it were dry.

Construction methods vary with site conditions. The most common form is a sheet pile cofferdam, created by driving interlocking steel, timber, or composite sheets into the substrate to form a continuous barrier. Rigid cofferdams use reinforced concrete or steel walls, while inflatable or pneumatic cofferdams employ air or bladder systems to create a watertight interior. The choice depends on factors such as water depth, soil type, duration of work, and environmental concerns.

Dewatering and operation involve pumping water from inside the enclosure to achieve a dry working area. Dewatering systems may include submersible pumps, wellpoint networks, and sump arrangements. Continuous monitoring of seepage, hydrostatic pressure, and structural integrity is essential, and access is provided through gates or removable closures within the cofferdam.

Applications include bridge piers and abutments, dam and lock works, port and marina construction, underwater foundation work, and rehabilitation projects. Cofferdams enable construction under relatively controlled conditions, reducing water ingress and allowing standard construction processes to proceed.

Limitations and safety considerations encompass cost, time, and the need for careful engineering to resist seepage and settlement. Potential hazards include flooding, engulfment, equipment damage, and environmental impacts such as turbidity and disturbance to aquatic life. Proper design, monitoring, and site management are essential for successful use.