Effects of Water Depth, Bottom Roughness, and Latitude on Tidal Flows and Bedload Transport

The effects of water depth, bottom roughness, and latitude on tidal boundary layers, as well as on the resulting bedload transport, were investigated using a one-dimensional vertical tidal model with a two-equation turbulence closure. The tidal model was verified against field measurements, including comparisons of tidal velocity ellipses and their orientation angles. It was observed that the water depth affects the tidal boundary layer substantially, leading to different orientation angles of the tidal ellipses, while the effect of the bottom roughness (for a given water depth) is more modest. The orientation angle was mapped out for a range of varying roughnesses and water depths, revealing that the orientation angle increases with larger water depths and decreases with higher roughnesses. The effect of the latitude on the tidal boundary layer was investigated for a given water depth (120 m) and fine sand roughness, indicating that the orientation angle increases as the latitude decreases due to the smaller Coriolis effect at lower latitudes. The bedload (for a given latitude and sand bottom roughness) was visualized through the tidal period for different water depths, demonstrating that bedload transport only takes place in the parts of the tidal ellipse where the shear stress threshold for bedload transport is exceeded. Furthermore, the bedload transport increases as the water depth decreases.