A Study on Process of Water Exchange in Inohana Lake

Abstract

During the summer of 2005, we carried out an intensive field survey of current velocity, salinity, temperature, and water density in Inohana Lake, Japan, which is a semi-enclosed and highly stratified estuary. Field and meteorological data were used to investigate the characteristics of currents, and to estimate water-volume and salt fluxes as a measure of water and material exchanges. We undertook a test using a simple box model based on the average salinity and river discharge, and obtained the exchanges of waters between Inohana and Hamana Lakes and within Inohana Lake, respectively. In terms of water exchanges between the two lakes and within Inohana Lake, wind effects were dominant over tide. In terms of water exchange rate between the two lakes, the water-volume flux was about five times as great as freshwater inflow. The water-volume flux between two lakes estimated from the box model showed good agreement with the observed ones by the ADCR In the box model, the contribution of advection was larger than that of diffusion for the vertical water exchange. The vertical salt flux was estimated using two methods: the direct estimation from field data and a turbulent diffusion model. The turbulent diffusion model showed good agreement with the direct estimation by removing fluctuations with frequency less than 0.2 Hz from the velocity and salinity data.