Dynamic sedimentation and geomorphologic evolution of the Laizhou shoal, Bohai sea, Northern China

As a headland associated sandbank off an unconsolidated coast cape in a progression process, the Laizhou shoal is just located at the coalescent position of the two tidal residual current circumferences, its formation and maintenance dynamics, sedimentation and geomorphology are different from the models proposed up till the present moment. Our findings indicate that: (1) the tidal residual tidal current circumferences are located along the flanks of the shoal itself instead of the flanks of the headland cape, and the sediments under the two circumferences are quite different from those at their coalescent position; (2) the sediments made up of the shoal have an ultimate resource of river sediment instead of an erosion recession cape or seafloor nearby, and are transported directly from the coastal zone through the wave-resulted coastal current rather than through the tidal residual tidal eddies; (3) the shoal continually migrates from southwest to northeast, extending into the Laizhou bay northwest the cape in the past 50 years; (4) because more than 100 reservoirs have been built across the rivers in the northwestern Shandong peninsula, and have greatly reduced the sediments (especially gravel and sand grains) transported into the coastal zone, some locations of the shoal have evolved from deposition to erosion, and the shoal itself has become narrower, but has not evolved from deposition to erosion as a whole.