ABSTRACT

The Mississippi River-Gulf Outlet is a channel 36 feet deep and 500 feet wide which extends from a point south of Michoud, Louisiana southeastward across the marshes and Breton Sound and into the Gulf of Mexico. It was constructed by the U. S. Army, Corps of Engineers to provide additional access to the Port of New Orleans and thereby ease traffic on the Mississippi River. The channel crosses a delta lobe constructed where the Mississippi River flowed down a course located to the east of its present course. The sedimentary environments and the features formed by the destruction of the now abandoned and subsiding lobe have a great influence on sedimentation in the outlet and, conversely, the outlet has had a profound effect upon the environments on which it has been superimposed. The outlet has encountered an excessive amount of shoaling in its Breton Sound reach. In an effort to determine the cause(s) of the shoaling and the source(s) of the shoal material, a study was made of the several factors influencing sediment distribution in the Breton Sound area (e.g. tides, winds, spoil, and sediment distribution, salinity, current directions and velocities). The principal source of the shoal material was determined to be the spoil dredged from the outlet itself which returns to the channel as a density flow rather than by normal deposition of suspended material.