The Influence of Freshwater Discharge and Wind Forcing on the Dispersal of River Plumes Using a Three-Dimensional Circulation Model

Abstract

Tidal estuaries provide crucial pathways for contaminant transport. The salinity levels in estuaries and coasts are conserved substances that function as natural tracers to easily understand the offshore transport of substances that are subject to environmental factors. A three-dimensional (3D) circulation and mass transport model were utilized to delineate the salinity plume in a tidal estuary and continental shelf. The numerical modeling results were compared with the tidal amplitudes and phases, velocities, and salinities at different gauging stations in 2017. Quantitatively, the simulation and measurement results are in reasonably good agreement. Furthermore, the validated model was adopted to estimate the recovery times in tidal estuaries that are subjected to extreme freshwater discharges that come from the upstream reaches during typhoon events and to analyze the influences of freshwater discharge and wind stress on the river plume around the continental shelf. The simulated results revealed that the salinity recovery time at the river mouth due to Typhoon Saola in 2012 was less than 8 days. Increased inputs from freshwater discharge resulted in changes in the distances and areas of the river plumes. Linear regression relationships between the plume distance/plume area and the total freshwater discharge inputs were established. Neap and high slack tides were associated with the maximum plume distances and areas. Excluding tidal forcing resulted in larger plume distances and areas compared to the case in which tidal forcing was considered. The southward-favorable and northward-favorable plumes were controlled by northeasterly winds and southwesterly winds, respectively. The relative importance of freshwater discharges and wind forcing was explored. The results indicate that freshwater discharges frequently dominated the river plume, except when strong southwesterly or northeasterly winds prevailed.

Turbulent Kinetic Energy Production in a Far‐Field River Plume Under Upwelling‐Favorable Winds

“…Jurisa and Chant (2013) show that the width of the river plume is proportional to the river discharge. Plume areas have a linear relationship with freshwater discharge (Liu et al., 2022). The offshore velocities are larger at the estuary mouth, due to the larger barotropic pressure gradient in this area, which is the same as the results by Gong et al.…”

Numerical assessment of hydro‐morphodynamics affected by altered upstream discharge in the Dujiangyan reach of the Min River, China

“…Furthermore, the grain‐size distribution of the bedload and bed material were divided into nine size ranges, with the median of each range used in the calculations (Figure 6c). The thickness of the movable layer of the bed was set at 10 m, as recommend by Liu and Huang (2003) based on physical model. The Min River was set to have no bedload supply because the upstream supply is trapped by the Zipingpu Reservoir and we assume that the armour layer of the Min within the Dujiangyan reach is immobile and does not supply sediment to the bedload.…”

“…Guo and Zhang (1993) conducted a flume study and reported that the sediment trapping effect of the Zipingpu Reservoir had led to more severe erosion and instability of the Fish Mouth Levee and the Inner River, which required protection. Utilising a downscaled physical model, Liu and Huang (2003) suggested that the long‐term scour depth in the Dujiangyan reach due to the operation of the Zipingpu Reservoir would reach 2 m, with the bed being generally stable following this downcutting. With the regulation of the reservoir, the flow and bedload transport can be redirected to the Outer River, thereby reducing the negative impacts of floods on the Dujiangyan Irrigation Project.…”