To understand seawater exchange are important to analyze the formation of watermass, material circulation and transfer of pollutant material etc. The purpose of this study is to review the previous studies and to propose new exchange ratio. where,C1 ; average salinity of the water at low waterC2 ; average salinity of the water at the next low waterC0 ; average salinity of the water passing the bay mouth on the flood tideV2 ; total water volume of the bay on the low waterV0 ; the volume of the remaining outer bay water entering during the flood tideSeawater exchange ratio of Dongho Bay calculated by new method are 26.1%, 23.8% respectevely.The average fresh water residence ratio calculated by equation (12) is 2.2 days, that is corresponding 23.5 % of exchange ratio. Thus, it appears similar result as proposed exchange ratio.

The characteristics of tidal exchange in Masan Bay were studied on the basis of salinity observations and current measurements in the summer of 1985. The exchange ratio of the sea water was calculated using three different formulas. The tidal exchange rate was estimated to be smaller than that of another bays in the southern coast of Korea. The tidal exchange ratios in Masan Bay at spring tide were deduced to be 2.4-11.7%. While those at neap tide were 2.0-9.1%. Though tidal range of neap tide is smaller than that of spring tide. the tidal exchange ratio in the bay can be increased in case of highly stratified vertical structure.