Definition - What does Cofferdam mean?
A Cofferdam is a temporary enclosure which is built in pairs across or within a water body. It is constructed to allow the confined area to be pumped out. This creates dry work environment for major works to be proceeded. The enclosed coffers are generally used for the repair and construction of bridge piers, oil platforms and other structures which are built over or within the water. They are used in ship repair industries and in shipbuilding when a ship cannot be put into drylock to be repaired or altered. There are various types of cofferdams – some are enclosed kind of boxes placed in water and others are used for supporting excavation operations.
Petropedia explains Cofferdam
To construct a dam two cofferdams are generally built, one is downstream and the other is upstream of proposed dam. After the alternative diversion, channels or tunnels are provided for river flow to pass the dam foundation area. These are commonly the conventional berth dams of both rockfill and the earth; however some sheet oiling or concrete can be used. Usually, on completion of the dams and associated structures, downstream coffers are removed and upstream are flooded as diversions are closed and the reservoirs start to fill. Based on geography of the dam site, sometimes U-shaped cofferdams are used to construct one half of the dam. On completion the cofferdam is removed and another similar cofferdam is created on the opposite side of the river for constructing the dam's other half.