Hydrodynamics and sediment transport in normal weather: examples from a macrotidal tidal flat-channel system, Rudong, Jiangsu

Abstract

A detailed understanding of the hydrodynamics and sediment transport mechanisms of the intertidal mudflat-channel system can better predict its future survival and development potential. This study selected a typical open-coast macrotidal mudflat, Xiaoyangkou tidal flat in Rudong in the central part of Jiangsu Province, as the studied area, with field observations conducted on the tidal mudflat-channel system during tidal cycles. The study revealed wind waves generated by winds of around 7 m/s within a fetch length of 5 km can cause significant erosion on the mudflats during neap tides. Wind waves cannot cause erosion on the thalweg within the tidal channels and the lower parts of the banks under normal weather conditions. The peak flow velocity in the flood and ebb within the tidal channels occurs below the bankfull depth. Three different types of erosion processes were observed on the channel slopes: (1) Small-scale erosion on slopes of less than 10 cm in width and less than 5 cm in depth, causing widening and deepening of small tidal gullies, leading to vertical erosion of the slopes. (2) Medium-sized tidal creeks with 10–100 cm widths and depths of 5-100 cm experiencing sliding erosion. (3) Large tidal channels with widths greater than 200 cm and depths greater than 100 cm are more likely to toppling collapse. Continuous waves caused by wind oscillations below the bankfull depth at the observed cross-section of the tidal channels may be the main cause of erosion on the channel banks.