Bottom Boundary Layer Sediment Transport Processes in Fourleague Bay of Louisiana and Their Implication to Sediment Diversion and Coastal Restoration

Jiaze Wang1, Kehui Xu2,3, Samuel J Bentley3,4 and Giancarlo A. Restreppo4, (1)University of Maryland, Center for Environmental Science, Horn Point Laboratory, Cambridge, MD, United States, (2)Louisiana State University, Department of Oceanography and Coastal Sciences, Baton Rouge, LA, United States, (3)Louisiana State University, Coastal Studies Institute, Baton Rouge, LA, United States, (4)Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA, United States
Abstract:
Building land with a rising sea is a challenging problem in many major deltaic systems around the world. The Atchafalaya deltaic area is one of only a few growing sites in Louisiana coast. The sediment delivered to this deltaic area is mainly from three reservoirs: (1) sediment derived from ongoing fluvial delivery; (2) mobile sediment delivered to the coastal basin during the past year by cold fronts, tropical cyclones, and others; (3) more consolidated sediment stored in the seabed or bay floor for more than 12 months. In order to better understand the far-field dispersal and deposition of fine sediments in the Atchafalaya system, two tripods were used to study the hydrodynamics and sediment dynamics at two stations in Fourleague Bay, which are 15 km southeast of Atchafalaya Delta. One tripod was located at the middle of the bay, and the other was near the marsh edge. Six sensors including OBS (Optical Backscatter Sensor) 3A, OBS 5+, ADV (Acoustic Doppler Velocimeter) Ocean, Argonaut ADV, and two wave gauges were planned to deploy in the early summer and winter of 2015 for a month, respectively. Our study was focused on the near-bed sediment transport from each of the above three reservoirs to wetlands under fair weather and event condition. Based on the seasonal surface suspended sediment concentration (SSC), salinity, as well as turbidity, wave and current data, we have investigated the bottom boundary layer sediment dynamics, in order to illustrate sediment deposition and erosion processes under fair weather and energetic conditions in the bay. During an energetic event in early summer 2015, strong southeasterly wind waves carried salty water from inner Louisiana shelf northwestward into the bay, and led to increasing wave height, bottom shear stress, salinity, and near-bed turbidity. After the event, there was apparent decreasing of these parameters. SSC data in the bay showed an increasing trend since April, which is probably related to the fine sediment dispersal from the deltaic area due to the river flow. These onshore and alongshore transport events play a key role in trapping fine grained sediment and thus building land in coastal Louisiana.
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