The sewage dispersion in the radial sand ridges in the southern Yellow Sea is simulated using a particle-based method based on a three-dimensional numerical model. Six source points, where different tidal currents dominate, are considered. The particles released in Huangshayang Trough, which is dominated by the rotational tidal current, show more diffusive characteristics than those released in Xiyang Trough, where the tidal current is bi-directional. The fraction of total wastewater that originated from different tidal troughs is calculated, which indicate that the source contributions to total wastewater content in Xiyang Trough are nonlocal.
The radial sand ridges (hereafter indicated as "RSRs") over the Jiangsu Coast (Fig. 1), cover an area of more than 200 km from north to south and approximately 140 km from east to west. The RSRs consist of more than 70 sand ridges with various dimensions radiating from the Jianggang towards the open sea (Wang, 2012). Since was initially observed in the 1950s, this area has received extensive attentions for its complicated hydrodynamics and peculiar geomorphology (He, 1979). Several large-scale field surveys have been conducted in terms of the hydrology, geomorphic characteristics, coastal climate and so on (e.g., Ren, 1986; Wang, 2002; Zhang et al., 2012). On the other hand, various numerical models have also been developed and applied to study the hydrodynamics and sediment dynamics in the RSRs (Zhang et al., 1999; Zhu and Chang, 2001; Xing et al., 2012).
The tidal currents in the RSRs are dominated by two different tidal wave systems, which are determined by the land boundaries of China and Korean Peninsula. As the progressive tidal wave from the Pacific Ocean enter the Yellow Sea, part of the wave is reflected by Shandong Peninsula forming a rotational tidal wave system. This rotational tidal wave meets the following progressive tidal wave, resulting in the formation of an approximately stationary tidal wave. This stationary tidal wave converges to the central region of the RSRs leading to remarkably large tidal range and current speed (Zhang et al., 1999). Moreover, the tidal currents and the underwater topography both show significant regional differences between the southern and northern part of the RSRs, which is correspondent to the distribution of the two tidal wave systems (Xu et al., 2016).