Intensified sediment transport by breakdown of discharge-induced two-layer circulation in a contaminated, macro-tidal...

Freshwater discharge from sluice gates can enhance tidal asymmetry and form a two-layer circulation. In-situ observations using acoustic Doppler current profiler and CTD were conducted to investigate the effects of discharge on the sediment dynamics in a contaminated, macro-tidal Asan Bay. Continuous discharge during the early flood tide induced a two-layer circulation, characterized by a seaward surface current and a landward bottom current. During neap tide, as the two-layer circulation broke down after discharge was nearly complete, the landward current velocity near the bed reached up to 0.53 m s^-1, comparable to spring tide, and the landward sediment flux was approximately twice that during spring tide. The enhanced vertical mixing likely caused strong sediment resuspension, which remained trapped near the bed due to the intensified baroclinic forcing. These mechanisms potentially led to the intensification of landward sediment transport and accumulation of contaminated sediments in the inner regions of the bay.