Monitoring tidal flat dynamics affected by human activities along an eroded coast in the Yellow River Delta, China.

The coast of the northern Yellow River Delta (YRD) has experienced significant erosion since 1976 due to avulsion and consequent lack of sediment supply. Moreover, massive reclamation activity, expansion of the oil industry, and sea-level rise have jointly contributed to the rapid change of tidal flats over recent decades. Therefore, accurate reporting of the coast spatial extent and stability status is urgently required. We presented a method using remotely sensed waterlines to map tidal flats and monitor their spatiotemporal dynamics. The empirical results show that the area of the intertidal zone west of Tiao River Mouth (TRM) appeared to be decreasing. Despite intense hydrodynamic force, the intertidal zone to the east of TRM has expanded due to law prohibiting land reclamation in nature reserve. However, this trend weakened due to the expansion of oil industry after 2007. The movement of the mean high-tide line is the main cause for the increase-decrease patterns of the intertidal zone area. To achieve and maintain land equilibrium in this area, we suggest that a 554-m buffer must be preserved for mean high-tide line retreat. Unfortunately, the shrink crisis of the tidal flats has been extremely severe. Future reclamation and oil projects must be supplemented by studies that evaluate the complexities and dynamics of tidal flats so as to prevent the loss of this unique ecosystem.