Abstract
This paper describes density intrusion which influences water quality in Ohfunato Bay. Field experiments were carried out to directly measure the change in the DO concentration and velocity due to density intrusion which appears over a sill around the bay mouth. As suggested in the previous studies, it is found from the field experiments that density intrusion occurred during the flood tide and the DO concentration on the seabed is greatly influenced by the density intrusion since the high DO concentration water can be brought into the deep water region by the density intrusion. A non-hydrostatic three-dimensional LES model was used to analyze the effect of the density intrusion. The computation was verified from the comparison with the observed velocity. It is revealed from the computation that the front of the density intrusion can rapidly propagate into the seabed around the centre of the bay and the density intrusion may change the DO concentration on the seabed in a few hours.
