Cofferdam
temporary construction preventing water passage
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.
These cofferdams are usually welded steel structures, with components consisting of sheet piles, wales, and cross braces. Such structures are usually dismantled after the construction work is completed.
The origin of the word comes from coffer (originally from Latin cophinus meaning 'basket') and dam from Proto-Germanic *dammaz meaning 'barrier across a stream of water to obstruct its flow and raise its level').
The term is also used in naval architecture, to refer to a space between two watertight bulkheads or decks within a ship.
Uses
For dam construction, two cofferdams are usually built, one upstream and one downstream of the proposed dam, after an alternative diversion tunnel or channel has been provided for the river flow to bypass the foundation area of the dam. These cofferdams are typically a conventional embankment dam of both earth- and rock-fill, but concrete or some sheet piling also may be used. Usually, upon completion of the dam and associated structures, the downstream coffer is removed, and the upstream coffer is flooded as the diversion is closed and the reservoir begins to fill.
“Cofferdam” enters the record as temporary construction preventing water passage. Crown Archives preserves that source wording while asking what Cofferdam, temporary and construction can confirm, complicate or overturn.
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This entry incorporates text from “Cofferdam” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.