Seasonal and interannual evolution of geomorphology in middle Jiangsu tidal flat from 2017 to 2020

To investigate the seasonal evolution patterns of geomorphology in the middle Jiangsu tidal flat, three cross-shore profiles along the Jiangsu coast were selected: one on the south side of Dafeng Harbor, one on the north side of Dafeng Harbor, and another on the north side of the Sheyang River estuary. A series of repeated observations in geomorphology and surface sediments were conducted from November 2017 to November 2018, and the interannual variations of the three profiles were monitored from 2017 to 2020. Results reveal that the tidal flat on the south side of Dafeng Harbor exhibited relative stability in spring and autumn, but experienced more noticeable erosion in winter and summer, being overall stable throughout the year. In contrast, the tidal flat on the north side of Dafeng Harbor experienced evident erosion throughout the entire year, while the tidal flat near the Sheyang River estuary showed slight erosion year-round but remained relatively stable overall. From 2017 to 2020, the erosion and deposition changes in the three profiles exhibited a consistent trend. From 2017 to 2018, all tidal flats near Dafeng Harbor experienced overall erosion, while the tidal flat near the Sheyang River estuary showed siltation in the upper part of the intertidal zone and erosion in the lower part. In the following period from 2018 to 2019, varying degrees of siltation were observed in the middle Jiangsu tidal flat. From 2019 to 2020, all the tidal flats in the middle Jiangsu coast showed stabilization or slight erosion in the upper part of the intertidal zone and obvious erosion in the lower part of the intertidal zone. The analysis of the tidal flat evolution state reveals several key points. (1) The seasonal changes in the middle Jiangsu coast’s tidal flats are influenced by multiple factors. Winter wave intensification and increased storm frequency in summer contribute to seasonal erosion, while reduced sediment supply leads to an overall erosion trend. (2) The division point between erosion and deposition in the northern part of the Jiangsu tidal flat appears to have shifted southward from the Sheyang River estuary to the southern part of Dafeng Harbor. (3) The middle Jiangsu tidal flats exhibit a relatively consistent variation pattern on interannual scale.