NUMERICAL SIMULATION OF SALINITY DISTRIBUTIONS IN THE YATSUSHIRO SEA BY POM COMBINED WITH WATERSHED MODEL FOR B-CLASS RIVER BASIN

Minamata Bay, located in the southeast coastal areas of the Yatsushiro Sea, was heavily polluted due to the discharge of organic mercury compound from a chemical factory since 1932. Some research has demonstrated that correlations between seawater characteristics and methyl-mercury concentration are observed. Based on the analysis of low-salinity water masses in the Yatsushiro Sea, this paper deals with salinity field in the Yatsushiro Sea under the effect of freshwater from rivers by Princeton Ocean Model (POM) combined with watershed model. Firstly POM is established covering both the Yatsushiro Sea and the Ariaka Sea. Salinity fields in six cases are calculated under freshwater inflow from a A-Class river: the Kuma River. Then a watershed model is applied in basin of a B-Class river: the Komenotsu River for Case5 and Case6. Rainfall data and physical characteristics of catchment are utilized to estimate river's discharge by Kinematic Wave Method (KWM). Through the computation, it's indicated that simulated salinities in surface layer exhibit the same trends as the measured ones at most cases. The deviations in Case1-Case4 are less than 20% at most areas, but the deviations become obviously higher in Case5 and Case6 when the measured salinities are lower than 5 and the highest deviations always occur in surface layer. Adding the Komenotsu River's discharges into POM, salinities at two stations (St.25 and St.26) in Case5 and one station (St.26) in Case6 have decreased owing to the rainfall and closer location to the river mouth.