Predicting Wave-Induced Sediment Entrainment by Liquefaction Degree

Abstract:

Wave-seabed interaction is known to be a fundamental factor for the stability, entrainment and transport of sediments. We present data of observed pressure and acoustic backscatter near the seabed from a storm event in May 2013 in the northern Gulf of Mexico, offshore of Panama City Beach, Florida. An existing poro-elastic wave-sediment interaction model in combination with a sediment failure criterion due to liquefaction (loss of vertical effective stress) is used to introduce the concept of liquefaction degree. It is defined as the portion of vertical effective stress at the sediment surface that is counteracted by wave-induced pore pressures. The relationship between wave-induced pressure at the seabed and liquefaction degree is expressed by a complex transfer function, indicating the importance of the swell band with respect to infra-gravity and short-wave components. The liquefaction degree is used to construct and calibrate a dynamical relationship between wave action and acoustic backscatter measurements near the seabed, taken as a surrogate for suspended sediment concentration. Predictions of backscatter were highly accurate during most of the time span analyzed providing strong evidence for the importance of wave-induced seepage forces in describing sediment liquefaction and entrainment processes. We speculate that the inferred dynamic relationship between wave action and sediment concentration will improve the modeling of sediment transport, when added as a source (entrainment) and sink (deposition) term to a partial differential equation to model advection (currents) and dispersion (turbulence) in one or two dimensions along the seabed.