A tow moves a hopper barge carrying 48 cubic yards of concrete that will be placed beneath a dam shell already underwater as part of the Olmsted Locks and Dam construction project on the lower Ohio River. Filling the underside of a shell can require up to 6,000 cubic yards, or 400 truckloads, of concrete which is loaded onto hopper barges that are moved to the work platform in the river for load transfer beneath the surface. (U.S. Army Corps of Engineers photo)