Evolution of the topography of tidal flats and sandbanks along the Jiangsu coast from 1973 to 2016 observed from satellites

Understanding the evolutionary trends of tidal flat development is crucial for local ecological protection, tidal flat development and utilization. However, obtaining such knowledge is often challenging due to the lack of frequently updated topography. This is particularly true for the middle section of Jiangsu Coast, which has complex sedimentary features and is the largest and the most rapidly changing tidal flat area in China. In this study, long-term remote sensing images (1973–2016) and a recently developed method for generating a Digital Elevation Model (DEM) were combined to construct a historical topological dataset with 24 phases of DEM, which was used to track changes of the Jiangsu Coast during the past four decades. The results demonstrate that: (1) the slope of the Jiangsu Coast from north to south exhibits a prominent increasing trend during the past 40 years, with the high tidal flat moving seawards and the low tidal flat moving landwards. (2) Large offshore sandbanks (Dongsha Sandbank, especially) are generally undergoing erosion in both the high tidal flat and low tidal flat, with the exception of Gaoni Sandbank where the high tidal flat is still in accretion. (3) Although there are discernible differences in rate, almost all the small offshore sandbanks have moved in the principal direction of the tidal channels, in good agreement with an independent sediment transport model study. Our findings provide useful baseline information for both future researchers and local authorities, in support of future environmental management, coastal protection, and storm forecasting.