Unsteady Density Current in a Shallow Water Estuary

Abstract

Simultaneous measurements of three components of instantaneous velocity, salinities and water temperature have been performed during a spring tide in the Ota River estuary which demonstrates a large tidal range and density gradients induced by salinity. Data are collected at various distances from the bed. Stability influence of stratification changes widely during the tidal cycle. Around low water slack, the estuary is well mixed. On the other hand, the estuary strongly stratifies near the water surface after high water slack in the ebb tide. The longitudinal density gradient, which drives an upstream bottom flow, is essential throughout all tidal phases. Owing to the longitudinal density gradient, the ebb flows in lower layers are small and bed-generated turbulence is weak.