Impact of mild winds on morphological evolution in a macrotidal tidal flat-channel system: a case study from Rudong, Jiangsu, China

A detailed understanding of the hydrodynamics and sediment transport mechanisms of the intertidal mudflat-channel system is crucial for predicting its future survival and development. This study focuses on the Xiaoyangkou tidal flat in Rudong, located in the central part of Jiangsu Province, as a representative open-coast macrotidal mudflat. Field observations were conducted on the tidal mudflat-channel system during tidal cycles. The results show that wind waves generated by winds of approximately 7 m/s over a fetch length of 5 km can cause significant erosion on the mudflats during neap tides. However, under mild wind conditions, wind waves do not induce erosion on the thalweg within tidal channels or the lower parts of the banks. The peak flow velocity during both flood and ebb tides within the tidal channels occurs below the bankfull depth. Three distinct types of erosion processes were observed on the channel slopes: (1) Small-scale erosion on slopes less than 10 cm in width and 5 cm in depth, which leads to the widening and deepening of small tidal gullies and results in vertical erosion of the slopes. (2) Medium-sized tidal creeks, with widths of 10–100 cm and depths of 5–100 cm, experiencing sliding erosion. (3) Large tidal channels, with widths greater than 200 cm and depths exceeding 100 cm, are more prone to toppling collapse. Continuous wave action caused by wind oscillations below the bankfull depth at the observed cross-section of the tidal channels may be the primary driver of bank erosion.