In the coupled estuary–shelf system, plumes originating from the New Hu-Wei and Choshui rivers, consisting of many terrestrial materials, could contaminate the water of the Mailiao industrial harbor. To determine the contribution of the two rivers to pollution, the interaction between river-forced, tide-generating, and monsoon-driven water motions in and around the Mailiao industrial zone harbor was examined by performing a series of numerical model experiments. We used a three-dimensional general circulation model to examine the interplay between Asian monsoon-driven, river-forced, and tide-induced water motions, one of which could primarily affect the plume. The model-derived results for different river discharges revealed that almost all of the ammonium entering the harbor had a slope-positive trend, with oscillations in response to flood–ebb tidal cycles. The ammonium increased with time and flux, except for the 10 m³/s flux. Although the river discharge flux exceeded 200 m³/s, the ammonium entering the harbor was the same as that of the 200 m³/s flux; the ammonium concentration did not increase significantly with time after the flux exceeded 200 m³/s. In addition, irrespective of flood or ebb tidal currents being suppressed by strong Asian monsoons, this mechanism avoided contaminating the water quality of the harbor while northeasterly winds prevailed. By contrast, the southwesterly monsoon drove the geostrophic current northward along the coast; concurrently, the coastal sea level increased to form the surface isobar slope up toward the coast, producing a secondary flow to accelerate geostrophic alongshore currents. The northward geostrophic currents compressed the plumes shoreward, forming a relatively narrow-band plume; the coupling model demonstrated that the southwesterly monsoon-driven current pushed plumes favorably along the west pier into the harbor.

The present work employs a three-dimensional ocean model (MITgcm) driven by tidal and climatological forcings to assess the range of impacts of thermal wastewater discharge from the Third Nuclear Power Plant (NP_No.3) in Nan Wan Bay on the local ecosystem. Tides and daily wind forcings are incorporated into the MITgcm to examine their effects on thermal plume dispersion and water circulation in Nan Wan Bay. The model results reveal that the thermal plume is most likely to disperse to the southwest in the summer; it is unlikely to drift to the southeast or northeast because of the presence of the gentle southwesterly monsoon. In the winter, the thermal plume is most likely to be directed to the southwest and is unlikely to be directed to the northeast or southeast because of the prevailing northeasterly monsoon. Additionally, it is worth emphasizing that strong tidal currents generate a pair of counter-rotating eddies that significantly influence the dispersion of the thermal plume. However, seasonal monsoons also play an essential role in modifying the thermal plume’s direction and dispersion.

In order to assess the range of impact of thermal wastewater discharge from the third Nuclear Power Plant (NP_No.3) on the local ecosystem, a three-dimensional ocean model (MITgcm) driven by tidal and climatological forcings is employed to study the present work. Tides and daily wind forcings are incorporated into the MITgcm model to examine their effects on the thermal plume and the water circulation in Nan Wan Bay. The model results reveal that the thermal plume is most likely to disperse to the southwest in summer; it is unlikely to drift to the southeast or northeast because of the presence of gentle southwesterly monsoon. In winter, the thermal plume is most likely to be directed to the southwest but barely visible in the northeast or southeast directions because of prevailing northeasterly monsoon. Additionally, it is worth emphasizing that strong tidal currents generate a pair of counter-rotating eddies that significantly dominate the dispersal of the thermal plume. However, seasonal monsoons also play an essential role in modifying the plume’s direction and dispersion. The model results reveal that the flow field and thermal plume agree well with observational data.