Modeling sand wave migration based on the internal solitary wave induced internal-surface coupling response of seabed

Yueyue Lei¹Hu Wang^1*Hongxian Chu²Yongping Ji^3*

• ¹Tianjin University, Tianjin, China
• ²Observation and Research Station of Land-Sea Interaction Field in the Yellow River Estuary, Yantai, China
• ³China Coast Guard, Beijing, China

Migrating sand waves are widely developed on the outer continental shelf and upper slope of the northern South China Sea (SCS), at water depth ranging from 80 m to 250 m. Recent works reveal the critical role of internal solitary waves (ISWs) in sand wave migration in this area. However, the physical mechanism and mathematical modeling on ISW-induced sand wave migration still have deficiencies. This paper proposes hydrodynamic and seabed models utilizing the Massachusetts Institute of Technology General Circulation Model (MITgcm) and Biot's theory to evaluate bed load transports, in which the ISW-induced internal-surface coupling response of seabed is particularly considered. Results and analysis indicate that ISWs can induce excess pore pressure (EPP) in the seabed, resulting in upward seepage force acting on the sediment particles, and thus reduce the critical incipient shear stress and promote the initiation and transport of sediment at seabed surface. The ISW-induced transient EPP rather than the accumulated EPP dominates the internal pore pressure response of seabed. The ISW-induced erosion depth can be twice the transient liquefaction depth at the uppermost seabed layer if seepage force is added to the sediment force equilibrium equation. With the bottom shear stress outputted by MITgcm as the external driving forces, combining the internal-surface coupling response of seabed, the bed load transport rate is effectively calculated. This paper provides effective tools to evaluate ISWs-induced bed load transport and suggests an important role of ISWs in the migration of sand waves on the outer continental shelf and upper slope in the northern SCS. Further in-situ observations are still needed to calibrate and verify the present model.