NUMERICAL INVESTIGATION ON EFFECTS OF DISCHARGE, TIDAL FLUX, AND BATHYMETRY OF ESTUARY ON TYPE AND LENGTH OF SALINITY INTRUSION

抄録

 This study focused on the relationship between salinity intrusion length (SIL), mixing type, and basic properties (river discharge, tidal range, and bathymetry) of an estuary. Numerical experiments were carried out using a three-dimensional hydrodynamic model. A total of 26 numerical experiments were carried out, where 20 experiments with a conceptual model of a simple straight channel and 6 experiments with the Chikugo River estuary bathymetry. Variation of the SIL was discussed in terms of the tidal range and fresh water discharge. The time required to achieve the steady state of salinity intrusion was decreased with an increase in either discharge or tidal range. For a constant tidal range, SIL was decreased monotonically with an increase in the freshwater discharge, while for a constant discharge, SIL was a non-monotonic function of tidal range due to change in the mixing type. A diagram for classification of the mixing types was constructed as a function of tidal flux (TF) and gravitational flux (GF). GF is produced by the density gradient in the estuary. The mixing type of an estuary was salt wedge for TF/GF < 1.8, partially mixed for 1.8 ≤ TF/GF ≤ 3, and it was well mixed for TF/GF > 3.