Observations and analysis of giant sand wave fields on the Taiwan Banks, northern South China Sea

Understanding sand wave dynamics is of importance in marine science and also has relevance in engineering. Giant sand wave fields (wave heights up to 10 m) are not common and thus have been relatively rarely studied. This paper presents the first study on bedform changes related to giant sand wave geomorphology on the Taiwan Banks. Using data from three repeated multi-beam bathymetric surveys (2011, 2012 and 2013) and a spatial cross-correlation method, different sand transport patterns are obtained. Classical crest-perpendicular migration is observed in the small sand waves with migration rates of 1-5 m/a, and migration is parallel with the current direction. However, the giant sand waves are immobile over the observed periods, and along-crest transport sand transport has been observed that is perpendicular to the predominant current direction. Statistical results support these findings and thus illustrate a type of sediment transport pattern that differs from other sand wave fields around the world. It is concluded that the giant sand waves act as a bathymetric obstacle, thus changing the direction of bottom currents flowing over them, resulting in a change in sediment transport pattern on the Taiwan Banks.