Yuwu Jiang

Three-dimensional pollutant transport model for the Pearl River Estuary.

In this paper, the development and implementation of a three-dimensional, numerical pollutant transport model, which is based on an orthogonal curvilinear coordinate system in the horizontal direction and a sigma coordinate system in the vertical direction, is delineated. An efficient as well as simple open boundary condition is employed for pollutant transport in this mathematical model. It is then applied to model the distribution and transport of Chemical Oxygen Demand in the Pearl River Estuary. The results from the numerical simulations illustrate that the transboundary or inter-boundary effects of pollutants, between the Guangdong Province and the Hong Kong Special Administrative Region due to the wastewater discharged from the Pearl River Delta Region, are quite strong.

A three-dimensional pollutant transport model in orthogonal curvilinear and sigma coordinate system for Pearl river estuary

In this paper, the development of a three-dimensional numerical pollutant transport model, which is coupled with a previously developed hydrodynamic model, is delineated in details. Special features of the model include orthogonal curvilinear coordinate in the horizontal direction and sigma coordinate in the vertical direction. Besides, a simple but efficient open boundary condition of pollutant transport is adopted. It is then applied to simulate the transport of a representative water quality parameter chemical oxygen demand in Manganese (CODMn) in the Pearl river estuary, which is the largest estuary in South China. It can be shown, from the simulated results, that there exists a transboundary action between Guangdong province and Hong Kong special administrative region for the pollutants in the wastewater discharged from Pearl river delta region.

Integration of a GIS and a complex three-dimensional hydrodynamic, sediment and heavy metal transport numerical model

The paper presents an integration of a geographic information system (GIS) and a complex three-dimensional hydrodynamic sediment and heavy metal transport numerical model. The integration overcomes the two-dimensional constraint of conventional GIS by supplementing advance tools for three-dimensional, dynamic visualization. The application of a GIS-based interface module together with the three-dimensional, dynamic display tools enhances communication of relationships and trends of hydrodynamic and pollutant transport simulation in both spatial and temporal context, and thus promotes better coastal water quality planning and management. Model functionality includes input data viewing and editing, mesh grid configuration, and result interpretation. The functionality of the GIS-model integrated system is illustrated through a case study on the Pearl River Estuary (PRE).

Simulation of transboundary pollutant transport action in the Pearl River delta

The rapid economic development in The Pearl River delta region (PRDR) has exerted serious potential pollution threats to areas in the vicinity, which have complicated the task of environmental protection in Hong Kong and Macau. In this paper, a three-dimensional numerical pollutant transport model coupled with a synchronised numerical hydrodynamic model, is developed and employed to simulate the unsteady transport of a representative water quality variable chemical oxygen demand in The Pearl River Estuary. It is demonstrated that there exists a transboundary pollutant transport action between Guangdong Province and Hong Kong for the pollutants in the wastewater discharged from PRDR.

Winter bloom and associated upwelling northwest of the Luzon Island: A coupled physical‐biological modeling approach

For this paper, a coupled physical-biological model was developed in order to study the mechanisms of the winter bloom in the Luzon Strait (referred as LZB). Based on a simulation for January 2010, the results showed that the model was capable of reproducing the key features of the LZB, such as the location, inverted-V shape, twin-core structure and bloom intensity. The simulation showed that the LZB occurred during the relaxation period of intensified northeasterly winds, when the deepened mixed layer started to shoal. Nutrient diagnostics showed that vertical mixing was responsible for the nutrient supply to the upper ∼40 m layer, while subsurface upwelling supplied nutrients to the region below the mixed layer. Hydrodynamic diagnostics showed that the advection of relative vorticity (RV) primarily contributed to the subsurface upwelling. The RV advection was resulted from an offshore jet, which was associated with a northeasterly wind, flowed across the ambient RV field.

Coastal cape and canyon effects on wind-driven upwelling in northern Taiwan Strait

A combination of observations and numerical model is used to reveal the upwelling features and mechanisms in the northern Taiwan Strait during summer. In situ data give evidence of the upwelling in the form of thermocline tilting upward onshore. The remote sensing data show a strip of upwelling in the coastal region, which occurs more than half a summer. The upwelling probability map indicates there are two upwelling cores, one located downstream of Pingtan Island formed as cape effect and the other over the coastal canyon off the Sansha Bay. Remote sensing data and numerical model results suggest that the southerly wind plays a key role in shaping this upwelling strip, while the tides regulate the upwelling location through tidal mixing effect in the shallow water region, especially lee of Pingtan Island. Further numerical experiments using idealized cape and coastal canyon topography show that vertical velocity is intensified downstream of the cape and canyon. The vorticity equation shows that relative vorticity change along a streamline and frictional diffusion of vorticity are responsible for the vertical velocity off the cape and within and around the canyon. According to the conservation of potential vorticity, the variation of relative vorticity along a streamline over irregular topography, e.g., cape and canyon, is the main mechanism for the two upwelling cores in the northern Taiwan Strait.

The coastal ocean response to the global warming acceleration and hiatus

Coastlines are fundamental to humans for habitation, commerce, and natural resources. Many coastal ecosystem disasters, caused by extreme sea surface temperature (SST), were reported when the global climate shifted from global warming to global surface warming hiatus after 1998. The task of understanding the coastal SST variations within the global context is an urgent matter. Our study on the global coastal SST from 1982 to 2013 revealed a significant cooling trend in the low and mid latitudes (31.4% of the global coastlines) after 1998, while 17.9% of the global coastlines changed from a cooling trend to a warming trend concurrently. The trend reversals in the Northern Pacific and Atlantic coincided with the phase shift of Pacific Decadal Oscillation and North Atlantic Oscillation, respectively. These coastal SST changes are larger than the changes of the global mean and open ocean, resulting in a fast increase of extremely hot/cold days, and thus extremely hot/cold events. Meanwhile, a continuous increase of SST was detected for a considerable portion of coastlines (46.7%) with a strengthened warming along the coastlines in the high northern latitudes. This suggests the warming still continued and strengthened in some regions after 1998, but with a weaker pattern in the low and mid latitudes.

Prediction of sediment transportation in deep bay (Hong Kong) using genetic algorithm

The genetic algorithm (GA) is a powerful method which can be used to solve search and optimization problems. A genetic algorithm with tournament selection, uniform crossover and uniform mutation is used to optimize sediment transport parameters in this study. Two important parameters of sediment transport, the critical shear stress for deposition and resuspension, are optimized by GA. The results show that GA is efficient and robust for optimizing parameters of our sediment transport simulation of Deep Bay.

Numerical modeling of hydrodynamic changes due to coastal reclamation projects in Xiamen Bay, China

Xiamen Bay in South China has experienced extensive coastal exploitation since the 1950s, resulting in some severe environmental problems. Local authorities now have completed or are implementing many environmental restoration projects. Evaluating the cumulative impact of exploitation and restoration activities on the environment is a complicated multi-disciplinary problem. However, hydrodynamic changes in the bay caused by such coastal projects can be characterized directly and definitively through numerical modeling. This paper assesses the cumulative effect of coastal projects on the hydrodynamic setting using a high-resolution numerical modeling method that makes use of tidal current speeds and the tidal prism as two hydrodynamic indices. Changes in tidal velocity and the characteristics of the tidal prism show that hydrodynamic conditions have declined from 1938 to 2007 in the full-tide area. The tidal current speed and tidal prism have decreased by 40% in the western part of the bay and 20% in the eastern part of the bay. Because of the linear relationship between tidal prism and area, the degraded hydrodynamic conditions are anticipated to be restored to 1972 levels following the completion of current and proposed restoration projects, i.e. 33% and 15% decrease in the hydrodynamic conditions of 1938 for the western and eastern parts of the bay, respectively. The results indicate that hydrodynamic conditions can be restored to some extent with the implementation of a sustainable coastal development plan, although a full reversal of conditions is not possible. To fully assess the environmental changes in a region, more indices, e.g., water quality and ecosystem parameters, should be considered in future evaluations.

One-dimensional ocean model with three types of vertical velocities: a case study in the South China Sea

In this research, three vertical velocities were included in a one-dimensional (1D) ocean model for a case study of the SouthEast Asian Time-Series Study station in the South China Sea. The vertical velocities consisted three processes, i.e., Ekman pumping (WEK), Eddy pumping (WEP), and the background upwelling (WBK). The quantification of WEK followed the classical Ekman pumping theory. The WEP, whose underlying mechanism was consistent with the baroclinic modes (dominated by the first mode), was quantified by Argo observation and altimetry data. The WBK, related with the background circulation, was estimated from the long-term heat budget balance. The skill assessment indicated that the case with all three processes performed best. The study confirmed the capability of the 1D model with three types of vertical velocities, which can reproduce the general structure and variation of temperature in vertical direction.