Extensions of the river plume under various Yellow River courses into the Bohai Sea at different times

River plumes are formed when riverine freshwater spreads out over underlying saline oceanic water, influencing the water properties, circulation, marine ecological environment and fishery resources in the adjacent coastal waters. The Yellow River is the largest river that flows into the Bohai Sea, and since 1964 it has shifted its course three times. A 3-D numerical model was used to study the extensions of the Yellow River plume under the three river courses into the sea at three different times in its recent past, together with their seasonal variations. The residual water flux was calculated to better represent the net water transport in the shallow waters over individual tides. During the Diaokou course (c.1976), the river plume spread out near the river mouth and slightly deflected northwards in winter, while extending far southeastwards into the central part of the Bohai Sea in summer. During the Qingshuigou course (c.1996), the river plume was restricted within Laizhou Bay in both winter and summer under the Coriolis and buoyancy forces induced by the salinity front. During the Q8 course (c.2017), the river plume was confined within Laizhou Bay during winter while part of the river plume extended into Laizhou Bay and part of it extended into the central area of the Bohai Sea due to the eastward Ekman transport produced by the southerly wind in summer. The effects of wind, ambient current, bathymetric change, and river discharge on the extension of the Yellow River plume at different times in its recent history are systematically analyzed and discussed. The simulated clear differences of the river plume extensions under various courses of the river into the Bohai Sea at different times is fundamental for the better understanding and protection of the fishery resources.