Mississippi River Delta front loading mechanisms using non-linear wave modeling

Ioannis Y Georgiou, University of New Orleans, Department of Earth and Environmental Sciences, New Orleans, LA, United States, Samuel J Bentley, Louisiana State University, Baton Rouge, LA, United States, Kehui Xu, Louisiana State University, Department of Oceanography and Coastal Sciences, Baton Rouge, LA, United States, Jillian M Maloney, San Diego State University, Department of Geological Sciences, San Diego, CA, United States, MIke D Miner, Bureau of Ocean Energy Management, U.S Department of Interior, New Orleans, LA, United States, Gregory Paul Keller, Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA, United States and Jeffrey Obelcz, Coastal Studies Institute, Baton Rouge, LA, United States
Abstract:
River deltas often exhibit submarine slides caused by the nature of weak unconsolidated clays deposited through rapid fine grained sedimentation. The role of waves as trigger mechanisms has been suggested and studied by many previous efforts, highlighting among others; the effect of cyclic loading from large hurricane waves shoaling on the delta front seafloor, high near-bed orbital velocities resulting from these waves that can exceed 2m/s, and the development of a pressure gradient across a wave crest that can differentially load the seabed. With declines in suspended sediment load over recent time (1700-present) delta front degradation is inevitable, and recent works suggest that the MRDF is nearing that phase. The impacts of delta front degradation and the potential increase in submarine failures pose an important economic and societal risk to delta populations and infrastructure. Here, we revisit the pressure gradient as a possible loading mechanism for triggering submarine slides and failures. We extend previous studies by hindcasting waves from known hurricanes that influenced the delta using a fully non-linear fluid dynamics model. By controlling the wave properties at the seaward boundary (wave height, length, period) and the type of waves that are forced (linear-sinusoidal, and non-linear-cnoidal, higher order stokes) we examine the pressure gradients along a wave crest and compare with measured shear strength of delta front soils. We further our analysis by evaluating the potential increase in pressure gradients near the bed resulting from shoaling waves on the delta front, in combination with variations in delta-front slopes. Results suggest that the presence of non-linear waves creates larger pressure gradients over shorter wave lengths (or periods), which produce differential loading of the seabed due to transient pressures. Furthermore, our results suggest that the resulting transient pressures may be higher than previously reported, due to the rapid transformation of these waves on the delta front.
Back to: Sediment Dynamics in Coastal Settings: Observations and Modeling of Sediment Transport, Morphology, and Change on Event to Decadal Timescales IV