SEASONAL VARIATION CHARACTERISTICS OF CURRENT STRUCTURE AND QUANTITATIVE ANALYSIS OF SEAWATER EXCHANGE IN OHFUNATO BAY

摘要

This paper deals with the seawater exchange caused by the density gradient between the outside and inside of Ohfunato Bay using a density profile around the mouth of the bay and velocity profile above the breakwater mound which has been constructed on the bottom of the bay mouth. The field observations are carried out in order to realize seasonal characteristics of current structures and water qualities behavior in Ohfunato Bay. As a result, it is revealed that the mechanism of seawater exchange is greatly influenced by the density intrusion depending on the longitudinal density gradient. When the density of the outside of the bay is smaller than that of the inside, the seawater exchange occurs in the upper layer and cannot be expected in the lower layer. On the other hand, when the density of the outside bay becomes bigger than that of the inside bay, the seawater exchange is accelerated by two types of density currents. One is intrusion of the outside bay water, and the other is outflow owing to an entrainment above the mound.