Observations and Modeling of Wave‐Induced Burial and Sediment Entrainment: Likely Importance of Degree of Liquefaction

Abstract

AbstractWave‐seabed interaction is known to be a fundamental cause of sediment instability and entrainment. Observations of burial for surrogate munitions were made with a high frequency, sector scanning sonar acquiring acoustic images of the seabed every 12 min during a storm event in May 2013 in the northern Gulf of Mexico offshore of Panama City Beach, FL. Surrogate munitions burial depth was verified by divers. Driven by time series of pressure observed near the seabed, an existing poro‐elastic wave‐sediment interaction model in combination with a sediment failure criterion due to liquefaction (loss of vertical effective stress) was used to correctly estimate depth and timing of burial. We introduce the concept of liquefaction degree, which 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 was used to construct and calibrate a dynamical relationship between wave action and acoustic backscatter observations near the seabed, taken as a surrogate for suspended sediment concentration. Predictions of backscatter based on liquefaction degree were accurate at time scales of 15 s–30 min during most of the time span analyzed and superior to predictions of backscatter based on shear stress. The observations and analysis provide evidence for the importance of wave‐induced seepage forces in describing sediment liquefaction and entrainment processes.