Numerical simulation of residual circulation due to bottom roughness variability under tidal flows in a semi-enclosed bay

Nowadays there are some chronic serious environmental problems, such as eutrophication, blue fide and so on, in a complicated coastal zone or a semi-enclosed bay, because the water exchanges between an inner bay and an outer sea is weak compared with the supply of contaminant. Under this situation, a method to improve the water quality by 3-dimensional small unsymmetrical structures has been proposed by Komatsu et al. In this paper, several numerical simulations of the tidal current and concentration for various arrangements of bottom roughness in a semi-enclosed model bay are carried out with a depth-averaged 2-D numerical model. The model is solved by the hybrid finite analytic method with non-staggered grid. And the SIMPLES algorithm with Rhie and Chow's momentum interpolation technique is used for the simulation. The effect of Komatsu's method for water purification is examined by numerical simulation. The result of numerical experiment indicates that it is possible to generate a new tidal residual current and to activate a tidal exchange by bottom roughness arrangement only.