Physical conditions of saline water intrusion into a coastal lagoon, Lake Shinji, Japan

Abstract

In a coastal lagoon, Lake Shinji, saline water intrusion frequently occurs from the lower Ohashi River. Continuous observation of current velocity, salinity and water level in the Ohashi River revealed that intermittent intrusions takes place when diurnal periods of astronomical tide coincide with the rising stage of meteorological tides during a low discharge from the influent Hii River. The dynamics of tidal currents and saline transport in the Ohashi River were examined by numerical simulation with a simplified one-dimensional model using water level and salinity data from both river-channel ends. The calculated results reproduced well the observed time series of current velocity and salinity, though some disparity appeared under the two-layered structure. Related phenomena following the intrusion were described with respect to the formation of the stratified structure in Lake Shinji.