Impact of Near-Bottom Currents on Dredged Material Mounds Near Mobile Bay.

The Corps' Dredging Research Program (DRP) and the U.S. Army Engineer District, Mobile (CESAM) have continued monitoring dredged material deposits (berms) and environmental factors at the NBDP site. Repeated bathymetric surveys have documented gradual loss of material from the crests of two shallower sand berms. For 4 years, these berms remained as distinct forms, but migrated persistently north northwest, toward the coast. Surface wave buoys and bottom-mounted gauges recorded wave and current forces over this 4-year period. Instrument stations were maintained offshore, just seaward, and on top of the berms. This is the first report using measured waves and currents to investigate how large berms move. Several fundamental berm movement mechanisms are proposed and evaluated against the Alabama field measurements. The collected data are sufficient to reject some concepts of sediment movement that were previously relied on. The data suggest that two other proposed mechanisms are important. These findings help focus work on new mechanisms to better understand and predict long-term, large-scale sediment movement in open coastal environments.