Application of a three‐dimensional turbulence energy model to the determination of tidal currents on the northwest European Shelf

Abstract

A three‐dimensional turbulence energy tidal model, employing a sigma coordinate system through the vertical with a logarithmic type transformation to enhance near bed resolution, is used to examine M2 tidal currents on the European Continental Shelf. A no slip bottom boundary condition is applied in the model and vertical eddy viscosity is computed from a turbulence energy closure scheme. Comparisons of observed and computed current profiles, determined using the present model and an earlier model employing a spectral representation (Davies 1986) in the vertical, and a slip bottom boundary condition are made. In this spectral model a simple relationship between eddy viscosity and depth mean current was employed. These comparisons of current profile suggest that above the near bed layer the spectral model can reproduce tidal currents with a comparable accuracy to that of the present turbulence energy model. However, in the near bed region the turbulence energy model is significantly more accurate. Computed spatial distributions of current magnitude, turbulence energy intensity, and eddy viscosity show similar distributions over the model region, suggesting that a relationship between eddy viscosity and current intensity (the form used in the spectral model) is a valid alternative to using a turbulence energy model. Turbulence energy intensity, in particular, exhibits significant spatial variations both horizontally and vertically, with surface contours of turbulence corresponding to known positions of tidal fronts.