Erosion and siltation dynamics in an urban-influenced coastal setting, Xiamen Island, China

The evolution of seafloor erosion-siltation in urban bays has received wide attention owing to its high susceptibility to natural factors and human activity, Xiamen is a typical coastal city in China that has undergone rapid urban development. Here, we studied seafloor erosion-siltation in the sea to the east of Xiamen Island. In particular, we focused on the responses of erosion-siltation to changes in the natural environmental factors and intensive human activity. The spatial distribution and transport trends of surficial sediments, changes in sedimentary records, and erosion-siltation dynamics were analyzed based on surficial sediments, core sediment within a time span of ca.100 years, and new and historical bathymetric data. The results showed that surficial sediments were mainly transported to the northwest and southwest, three stage changes in sedimentary records have occurred, the shoreline gradually moved seaward and became straighter, and the erosion-siltation state shifted from slight erosion to siltation. Before the 1930s, climate change with alternating aridity and humidity controlled the influence area of the Jiulong River sediment input. During the subsequent period (1930s to the early 1970s) of enhanced human activity in the drainage basin, the increased river sediment input only promoted siltation in some of the study areas; however, after the 1970s, river sediment input was no longer a dominant factor in the evolution of erosion-siltation. During the rapid urban development in Xiamen, coastal development and construction on Xiamen Island resulted in a large influx of sediment into the sea directly. This compensated for the decreased river sediment input and shifted the study area toward siltation. Meanwhile, rapid siltation was triggered in some of sediment convergence areas and the Jinmen Channel, where the dredging and maintenance demands were low. While channel dredging and maintenance coupled with sediment back siltation caused significant short-term topography changes in the Xiamen East Channel. Land reclamation directly shrank tidal flats along Xiamen Island. Moreover, normal wind-generated waves and occasional intensification typhoon events affected the long-term evolution of these tidal flats via persistent erosion coupled with coastal transport, and drastic short-term erosion, respectively. •Riverine input fluctuated significantly under impact of natural and human activity.•Enhanced riverine sediment input only promoted siltation