Dune Migration on an Offshore Sand Ridge in the Southern Gyeonggi Bay, Korea

Two surveys were conducted in January 2006 and September 2007 with multibeam echosounder to investigate the dune shape, migration rate, and bedload transport rate using dune-tracking method on an offshore sand ridge at southern Gyeonggi Bay. The migration rates of dunes range from 1.8 myr 1 to 56.0 myr 1, at the upper northwestern side of sand ridge towards the southwest direction and from the center of the sand ridge towards the northeast direction respectively. Large (i.e. length 10-100 m) dunes show faster migration (0.3-23.4 myr 1) than very large (i.e. length > 100 m) dunes because larger dunes have required a larger volume of sediments to be displaced. The decreases in dimensions and migration rates of dunes from the center of sand ridge to the lower part of southeastern side on the sand ridge can be ascribed to the decrease of sandy sediments availability, tidal currents with depth, and the coarsening of surface sediments from the crest of the sand ridge to the trough. Bedload transport rates on the basis of migration rates and dune dimensions decrease from 74.5 m2yr 1 at C transect to 35.6 m2yr 1 at R-02 transect.