MOBILE, Ala. (WPMI) – To maintain certain depths in the shipping channel, the U.S. Army Corps of Engineers dredges approximately 4.1 million cubic yards of sediment from the stretch of the channel in Mobile Bay annually. Since 2014, the majority of that material has been put back in the bay using a method called thin layer placement, where no more than 12″ of sediment is spread out at least 2,500 feet away from the channel.