Evolution of a tide-dominated abandoned channel: A case of the abandoned Qingshuigou course, Yellow River

Deltaic river systems including both active channels and abandoned channels, are of significant importance to understand the deltaic morphology, as well as to the coastal management and ecosystem maintenance. However, the healing process of the abandoned channel has not yet been well understood. Based on the sedimentary record and hydrographic surveys, the deposit architecture and sediment dynamics of a tide-dominated abandoned channel, the abandoned Qingshuigou channel of the Yellow River, are investigated. The abandoned Qingshuigou channel has been fully disconnected from the main river channel since an artificial diversion completed in 1996. Twenty years after the abandonment, sedimentation with an average thickness of > 20 an was identified in the abandoned channel, illustrating a prominent seaward thickening trend from middle to lower channel. At the present river mouth of the abandoned channel, sedimentation layer with a thickness of 38 cm well matched the sedimentation rates derived from both chronological framework (1.85 cm/yr derived from Pb-210) and sedimentary facies (1.90 cm/yr). These deposits are composed by fine-grained sediment and enriched with organic matters, differing largely from the river-dominated deposits before abandonment. Tidal delivery of the sediment resuspended in the shallow water nearby Qingshuigou river mouth dominated the refilling process of the abandoned channel. Meanwhile, severe erosion near the abandoned river mouth shortened the channel (23.5 km in 1996 versus 14.5 km in 2018) and induced a lateral migration of the tidal inlet. Due to seasonally varying hydrodynamics, the tide-dominated abandoned Qingshuigou channel converts from a sediment sink in summer seasons to both a source and a sink in winter seasons.