A temporary wall-like structure which keeps water and soil out of a building site so that construction can proceed under dry conditions. Cofferdams are used in the construction of foundations, bridge piers, dams, dry docks, and similar structures which require dewatering and excavation of an area. The dewatered area can be completely surrounded by a cofferdam structure or a combination of earth slopes and cofferdam structure.

The type of construction is dependent on the site depth, soil conditions, fluctuations in water level, availability of materials, working conditions inside the cofferdam, and location either on land or in water. In most situations, since safety, ease of construction, and convenience are the most important considerations, and economy of materials is less important, refined methods of analysis may not be justified. However, an understanding of soil and water pressure against the cofferdam walls is necessary for even the most approximate design. Other important considerations in cofferdam design are the hydraulic analysis of seepage conditions (including filtering), and erosion of the bottom (scour) in streams and rivers.