Effect of tidal currents on the transport of saline water from the North Branch in the Changjiang River estuary

Abstract

Based on the MIKE 21 numerical model combined with measured data, a numerical model for the coupling of water and salinity in the Changjiang (Yangtze) River estuary was established, and based on good verification, the influence of the tidal current intensity on the transport and variations of salinity concentrations in saline water from the North Branch to the South Branch was numerically evaluated. The time and space mean root mean square of the tidal current velocity can be expressed as a parabolic function of an adjustment coefficient for the amplitude of the M2 tidal constituent along the open boundaries of the model. Under the advection of runoff and tidal currents, the saline pool is transported downstream in an oscillatory pattern. With the enhancement of tidal current intensity, the oscillatory motion of the saltwater pool is increasingly significant in a tidal cycle forced by rising and falling tides. Along four set paths, the daily average concentrations of the saline core were generally similar, and in the process of transportation downstream, the concentrations of saltwater declined. The decay of the tidal-period-averaged salinity of the saltwater was linearly related to the square of the tidal current. Thus, the tidal current has a significant and direct impact on saltwater transport and diffusion in the Changjiang River estuary.