Development of the water-purification method in Ohmura Bay by artificial bottom roughness

In order to purify water quality in a semi-enclosed bay, Komatsu et al. (1997) have proposed a new method for the control of pattern of tidal residual current by the arrangement of artificial 3-dimensional unsymmetrical bottom structures, in other word, "bottom roughness." A feasibility study has been carried out by the numerical simulation of tidal current in an actual semi-enclosed bay, Ohmura Bay, Japan, for several cases with/without bottom roughness by Yano et al.(2000) and it has become clear that the bottom roughness is able to control the tidal residual current arbitrarily. Ohmura Bay is divided into two parts, i.e. area near the bay mouth and the central area combined with the head of Ohmura Bay. In this research, advection-diffusion simulation was carried out by using the calculated results of tidal current simulation with/without the bottom roughness to confirm the effect of activation of tidal exchange between the two parts. The calculated results of transport of conservative substance as a tracer with bottom roughness were compared with the no-roughness case. From the results of this research, it has become clear that the artificial bottom roughness is able to activate tidal exchange significantly.