Cofferdam are temporarily dams. Biggest issues seem to be building ( and logistics) + deconstructing. But i saw an estimate of a cofferdam for a bridge of 640

Cofferdam are temporarily dams. Biggest issues seem to be building ( and logistics) + deconstructing. But i saw an estimate of a cofferdam for a bridge of 640 meters ( but less deep and with a single crane) of 16 days.