A cofferdam is an enclosure built within a body of water to allow the enclosed area to be pumped out or drained. This pumping creates a dry working environment so that the work can be carried out safely. Cofferdams are commonly used for construction or repair of permanent dams, oil platforms, bridge piers, etc., built within water.
A cofferdam on the Ohio River near Olmsted, Illinois, built for the purpose of constructing the Olmsted Lock and Dam
A cofferdam during the construction of locks at the Montgomery Point Lock and Dam
Inside of a cofferdam on a vessel
Marine salvage is the process of recovering a ship and its cargo after a shipwreck or other maritime casualty. Salvage may encompass towing, lifting a vessel, or effecting repairs to a ship. Protecting the coastal environment from oil spillages or other contaminants from a modern ship can also be a motivator, as oil, cargo, and other pollutants can easily leak from a wreck.
Marine salvage of a fishing boat off the coast of Estonia in 1973. Photo by Jaan Künnap
USS Regulus hard aground in 1971 due to a typhoon: after three weeks of effort, Naval salvors deemed it unsalvageable.
USNS Grapple, an example of a modern naval rescue salvage ship
Seawise University capsized after being gutted by fire in 1972
