SEDIMENT RE-ENTRAINMENT IN FINE-GRAINED DELTA FRONT SYSTEMS: WAX LAKE DELTA FIELD STUDY

Insights into transformative coastal processes are unlocked though understanding sediment transport mechanisms in fine-grained delta front environments. Movement of fine-grained sediments on delta fronts is not wholly explained through advection settling models. Standard advection settling models and associated laboratory experiments routinely underpredict the transported length of suspended sand by up to tenfold the distance found in delta front field studies. While advection settling models generally assume deposition into a still body, numerical modeling of sediment re-entrainment suggests there may be tidal, wave, and/or non-steady hydrograph influences allowing particles to reach greater distances by altering the decelerating velocity field. We hypothesize that a model incorporating re-entrainment of sediment through velocity altering conditions could explain the observed discrepancies in grain size fining trends along delta fronts. In this study we aim to develop a model, tested with field data from the Wax Lake Delta in Louisiana, USA, that more accurately accounts for controls on sediment transport in fine-grained delta front environments. Field data include suspended sediment profiles (using physical samplers and LISST-SL2 in-situ laser grain size and concentration instrument), flow velocimetry (using an acoustic Doppler current profiler), bed grab samples, and piston core samples. Initial results indicate incorporating sediment re-entrainment, due to a gradually decelerating velocity field, may be sufficient to produce grain size trends in this system; however, wave and tidal influences may also contribute to bringing sand farther out on the delta front. Continuing research aims to fully validate the numerical model to more accurately predict sediment concentration and depositional trends across the delta front in environments with greater wave and tidal influence.