GRAIN SIZE DISTRIBUTION AND TRANSPORTATION TRENDS OF BOTTOM SEDIMENTS IN THE SAND RIDGE FIELD OF THE SOUTH YELLOW SEA, CHINA

Grain size distribution and end-member-modeling algorithm analysis (EMMA) were conducted for the 117 bottom sediments taken from the radial sand ridge field (RSRF) of the South Yellow Sea. Sediment sources, transportation pattern and topography changes as well as the shifting of boundaries of the Yellow and Changjiang Rivers and their sediments diffusion pattern were studied for revealing the evolutionary trend of the radial sand ridge field and the siltation potential of the tidal flats. The RSRF region is dominated by silt and sand, though there is distinguished lateral variation. There occur silty materials in the subaqueous delta of the abandoned Yellow River, sandy silts in the northern RSRF, silty sands in the central RSRF, fine sands in the radial sand ridges, and more silty materials in the southern RSRF. The results of EMMA reveal that coarse silts from the Abandoned Yellow River Subaqueous Delta (AYRSD) and the Changjiang River have a significant effect on the bottom sediments of the RSRF. The fine materials from the AYRSD have been transported southwards and northeastwards, and the fine materials from the Changjiang River delta transported northwards, whereas the fine sands in the central RSRF have been transported southwards up to the foreshore area. Compared with the samples recovered from the RSRF during the surveys in 1980s and 1990s, fine materials in the whole study area are reduced and the sediments getting coarser as the result, showing an obvious trend of erosion.