Study on Salinity Intrusion and Mixing Types in a Conceptual Estuary Using 3-D Hydrodynamic Simulation: Effects of Length, Width, Depth, and Bathymetry

Abstract

In order to discuss the variation of salinity intrusion and mixing types in terms of estuary length, width, depth, and bathymetry, a total of 31 numerical experiments were carried out with a conceptual estuary by using a three-dimensional hydrodynamic simulator, Fantom-Refined. Since sand bars are formed in a river channel, and cyclic variation of the river bed height is found in longitudinal direction, sinusoidal wavy shapes were considered for rough bottom cases to represent the river bed with four different wave amplitudes (0.1, 0.2, 0.3 and 0.4 m) and wavelengths (350, 700, 1400 and 2800 m). In the cases of constant tidal range and discharge with the flat bottom, salinity intrusion length was decreased with increase in estuary length, and mixing condition was changed from salt wedge to well mixed type. On the other hand, salinity intrusion length was increased with increase in width of the channel under constant discharge. Further, the salinity mixing condition was changed from well mixed to salt wedge with the increase in depth of the channel. The salinity intrusion length was increased in the case of funnel shaped estuary when compared with the rectangular shaped estuary. Wavy bottom of the channel had less intrusion length compared with the flat bottom of the constant tidal range and discharge as the bottom friction reduced the velocity of the gravitational flow as well as enhanced vertical mixing. For the constant wavelength, the salinity intrusion length was decreased with increase in wave amplitude. On the other hand, for constant wave amplitude, the salinity intrusion length was increased with increase in wavelength.