Baroclinic two-layer flow induced by extreme discharge from a dam in a narrow channel

Long-term current observations were taken in the narrow Noryang Channel during extreme discharge and small discharge periods from a river dam. The Noryang Channel connects the west Gwangyang and east Jinju bays in southern Korea. Jinju Bay is relatively isolated from the open sea by many islands, whereas Gwangyang Bay is connected to the open sea through a wide, deep channel. Jinju Bay is closer to the river dam than Gwangyang Bay. The residual mean flow in the channel over the observation period showed a baroclinic two-layer flow as in an estuary during the large discharge period, whereas barotropic flow was present during the small discharge period. During the large discharge period, the upper layer of water flowed continuously westward, whereas the lower layer flowed eastward. Hydrographic data observed along the channel showed that Gwangyang Bay water was relatively saline and heavier during the large discharge period. This spatial difference in water density might be the result of a large inflow of discharge into Jinju Bay and relatively strong mixing between the water in Gwangyang Bay and the open sea. The salinity in the more isolated Jinju Bay was lower. Simple analytical model calculations showed that horizontal density difference during the large discharge period could drive the surface current flow westward, whereas that of the dense water of the lower layer in Gwangyang Bay flowed eastward through the Noryang Channel.