What is a water-tight inclosure, as of piles packed with clay, from which the water is pumped to expose the bottom (of a river, etc.) and permit the laying of foundations, building of piers, etc called?

cofferdam — A water-tight inclosure, as of piles packed with clay, from which the water is pumped to expose the bottom (of a river, etc.) and permit the laying of foundations, building of piers, etc. (Webster's 1913.)