A cofferdam is a temporary barrier that diverts water from an underwater site or retains soil so construction can be done. For example, building the substructure of a bridge or building foundation. Sheet-pile bulkheads are single or double-walled sheet pile structures consisting of interlocked steel sheets. After the cofferdam is constructed, the water inside is pumped out in stages and the steel sheets are further braced to strengthen the structure. Cofferdams are also useful in land-based projects when deep excavations are needed in tight spaces. McMullen and Pitz has an outstanding reputation for cofferdam work.