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Jin, C.; Gong, Z.; Geng, L.; Zhao, K.; Xu, B.B., and Coco. G., 2018. Subsurface processes in salt marsh of central Jiangsu coast(China). In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 296–300. Coconut Creek (Florida), ISSN 0749-0208. Studies of tidal flats morphodynamics tend to ignore subsurface processes like bioturbation or underground water dynamics so that changes in the surface elevation are always considered to be the result of sedimentation/erosion on the soil surface. However, at times, subsurface variations can be as large as elevation changes driven by sedimentation and so control the evolution trend of surface elevation. In this study, four observation sites were set up on the salt marsh in the central Jiangsu coast (China). A three-year field observation campaign has been carried out studying seabed elevation changes. The Surface Elevation Table-Marker Horizon (SET-MH) technique was applied to measure surface elevation and net sedimentation. The subsurface variation was derived from the difference between the surface elevation and the sedimentation. Results show that the changes in surface elevation are not equal to the sedimentation and that subsurface process, responsible for such deviation, are strongly affected by storm surge. Storm surges increase the underground water content leading to the observed expansion of the subsurface soil. The expansion results in the rapid increase of surface elevation and it takes almost one year to recover to the surface elevation before the storm season. [ABSTRACT FROM AUTHOR]

Radial sand ridges (RSRs) spread in a fan-shaped pattern over the seabed of the southern Yellow Sea along the Jiangsu Coast (China) with pronounced differences between the northern and southern channel-shoals (indicated as “NCS” and “SCS”, respectively). A depth-averaged nested numerical model is employed to analyze the tidal hydrodynamics and sediment dynamics of the RSRs. Model results show considerable regional differences in terms of tidal current vector ellipses: “eight-shaped” ellipses are typical in the NCS where rotational tidal waves dominate, while the SCS are characterized by “egg-shaped” ellipses because of the dominance of progressive tidal waves. Sand ridges tend to be elongated and straight in the NCS while short and dincontinuous in the SCS. Numerical Lagrange particles released near the ridges in the NCS tend to travel across the crest of the ridges rather than move around them as observed in the SCS. Consistently, the patterns of sediment convergence and divergence indicate that suspended sediments converge over the whole Xiaoyinsha Ridge located in the NCS, while converge to the two sides of the Hetunsha Ridge located in the SCS. Model results also highlight the importance of initial sediment compositions in determining patterns of the net sediment fluxes. The suspended sediment concentration (SSC) time series during one tidal cycle may show single or double peaks depending on the grain size and the related lag effect. Bed load transport is much smaller than suspended load. So sediment compositions should be carefully considered when simulating the SSC field, and the hydrodynamic of the morphological evolution of the RSRs at the regional scale. Overall, this study suggests that the NCS and SCS may be treated as two relatively independent geomorphological systems characterized by different tidal flows and sediment compositions. [ABSTRACT FROM AUTHOR]