An ultra-high horizontal resolution (about 200m) three-dimensional ocean model is developed to simulate the bottom current of observation area with size of 40 kilometers. The model takes tidal force, surface wind and baroclinic effect into account and adopts grid-nesting technique to achieve the horizontal resolution level. With the current simulated, a sediment transport model is developed and applied in the prediction of small scale sandwaves migration in study area of Beibu Gulf, South China Sea. The migration directions both on the ridge back and the ridge groove that are opposite are successfully predicted.
The sand waves, with wavelengths from tens of meters to kilometers and heights of several meters, can be found in many sandy shallow seas. Unlike static sand ridges and sandbanks, the sand waves often migrate with speed of up to some tens of meters per year (Nemeth et al, 2002; Besio et al, 2004; Lin et al, 2009a). Their dynamics can endanger some economical activities, such as cables exposed, pipeline spanned, and sea-route stemmed, etc. Many researchers assumed that interactions of oscillatory tidal flow and an erodible bed should be responsible for the sand wave formation and migration (Hulscher, 1996; Komarova and Hulscher, 2000; Nemeth et al, 2002; Besio et al, 2004; Lin et al, 2009a; Lin et al, 2009b). Hulscher (1996) demonstrated with a three-dimensional morphodynamic model, assuming a constant turbulent viscosity. Komarova and Hulscher (2000) improved this model into a turbulence model, which allows for a variable thickness of the current boundary layer. Later, Nemeth et al (2002), Besio et al (2003, 2004) disrupted the basic symmetry tidal flow and developed an asymmetric vertical circulative water motion model induced by the interactions between steady current or higher frequency constituents and sinusoidal tidal flow.
