SEDIMENT TEXTURE, TRANSPORT, AND DEPOSITION IN BRETON SOUND, MISSISSIPPI RIVER DELTA

In an effort to combat subsidence and sea level rise of the Mississippi delta and to enhance fisheries production, several diversion structures have been constructed along the lower Mississippi River. Breton Sound estuary encompasses roughly 1000 km² of fresh, brackish, and saline marshes located east of the Mississippi River. This region is underlain by Holocene Mississippi deposits of the Plaquemines-St. Bernard delta complex, which were active between 750-500 and 2000-3000 years ago, respectively. The Caernarvon diversion structure was completed in 1991 for freshwater control to compensate the sea water intrusion from the Gulf of Mexico. However, some studies have found this diversion also incidentally contributes a significant amount of mud to the Breton Sound area. This site is also a proposed future large diversion area in Louisiana’s Coastal Master Plan in 2012. Since water quality conditions are closely related to sediment transport processes, including sediment settling and erosion, and sediment properties (grain size, porosity and density), understanding the sediment transport processes is key to the study of wetland ecological evolution. In this study we compile historical grain size, turbidity, salinity and sediment transport data of Breton Sound, synthesize the data, and identify the knowledge gap. Our grain size analysis of the Breton Sound estuary shows that the mud-dominated estuary is under the control of nonlinear processes and various local conditions. Our study help establish a 3-D sediment transport model which will be focused on the impact of sediment concentration on light attenuation which controls photosynthesis rate and the influence on biological process in the Breton Sound estuary.