What does cofferdam mean?
A cofferdam is a temporary, watertight structure built inside a body of water — a river, lake, harbour, or the sea — so that the enclosed area can be pumped dry and construction can proceed on dry ground. Engineers commonly build them from interlocking steel sheet piles, though timber, earthfill, rockfill, and concrete versions exist, and they are essential for works such as bridge piers, dam foundations, dock repairs, and pipeline crossings. Once the permanent structure is complete and self-supporting, the cofferdam is usually dismantled or removed. In shipbuilding, the word also refers to a narrow sealed compartment between two bulkheads, designed to stop oil or water spreading through a hull. The term carries a practical, engineering register rather than literary colour, but it appears regularly in news coverage of major infrastructure projects, making it a useful word for anyone following civil engineering or maritime construction.
nounA watertight enclosure built within or around a body of water, typically from sheet piling or earth, that is pumped dry so construction work can be carried out on the exposed bed.
- A watertight temporary enclosure built in water and pumped dry to allow underwater construction, such as bridge piers, dams, or ship repairs.
- A sealed double-walled compartment on a ship's hull or between bulkheads, used to prevent leaks from spreading (nautical sense).
"Engineers sank a cofferdam into the riverbed before pouring the bridge foundations."
"Workers drove steel sheet piles into the riverbed to form a cofferdam around the pier site."
"The old freighter was fitted with a cofferdam to contain any seepage near the engine room."
Regular plural; used when referring to multiple enclosures at different sites or compartments aboard ships.
"Two separate cofferdams were built on either side of the weir during the reconstruction."
Without cofferdams, icons like the Brooklyn Bridge and the Statue of Liberty's pedestal might never have risen from the water — they let builders drain the sea itself.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cofferdam
Cofferdam combines 'coffer', a chest or casket, with 'dam'. 'Coffer' derives from Middle English cofre, borrowed from Old French, ultimately from Latin cophinus, meaning a basket, which itself came from Greek kophinos. The compound arose in English by the early 17th century, when engineers needed a term for these box-like enclosures set into waterways; it reflects the image of a great watertight chest placed in a river and emptied of its contents.
How cofferdam is actually used
Chiefly a technical term of civil engineering, dredging, and shipbuilding; rare in everyday conversation. Plural is regular: cofferdams.
Easily confused with cofferdam
A caisson is a sealed, often pressurized chamber sunk into place, whereas a cofferdam is an open enclosure pumped dry and removed after construction.