Impacts of relative sea level rise on the shoreface deposition,Shuidong Bay,South China

The influence of relative sea level rise on shoreface deposition helps to elucidate changes in beach and nearshore geomorphology in response to different forcing factors. In this study, two sets of sediment samples, one from 1982 and one from 2004, from the Shuidong Bay of South China were analyzed to determine the changes in shoreface depositions. An EOF (Empirical orthogonal function) method was used to examine how these depositions changed based on the relative sea level rise. The results show that shoreface sediments of Shuidong Bay are mainly composed of sand. Fine-grained sediments are distributed in the lower shoreface/offshore area, and coarse-grained sediments are mainly found in the upper shoreface/nearshore area. Due to the altered hydrological forcing caused by relative sea level rise, the sand fraction in sediments increased from 84.7 % in 1982 to over 90 % in 2004, and the clay and silt fractions decreased from 11.8 % in 1982 to 5.6 % in 2004. Grain-size parameters in sediments in 2004 became coarser, slightly more well sorted, less skewed and had lower kurtosis than those in 1982. In addition, the shoreface deposition of Shuidong in 1982 and 2004 is distinctly different: a polarized mode was described by the first eigenfunctions, and a homogenized mode was described by the second eigenfunctions. The former means that the sediment components developed towards the two opposite poles, undergoing both coarsening and refining processes. The second mode indicates that the secondary variation in sediment components was mostly in the three intermediate-grained sand components. In the future, the Shuidong Bay shoreface may be subjected to even further erosion because of increases in the energy of the environment resulting from rapid relative sea level rise.