Study on Multilayer Model Development for Density Current Simulation in a Tidal River

Abstract

In order to take fresh water from a tide river, it is necessary to clearly understand the salinity intrusion, which periodically changes according to the river discharge, tidal fluctuation and density difference. In this study, a new model having multilayer structure was developed to simulate the salinity intrusion phenomena. The model is aiming at calculating flow simply and shortly by employing new calculation techniques for vertical mixing and for boundary calculation at the river mouth. In addition to such techniques, density equivalent method was developed. In the method, thickness of each layer is changed, while density of each layer is kept unchanged in order to show the vertical density distribution. Based on such calculation ideas, the model is capable of simulating various mixing patterns caused by interaction of tide and fresh water flow. Field measurements were also carried out in the Tama River to examine the performance of the model. It was confirmed that the model could simulate the density current with enough accuracy through the comparison of numerical and observed results.