ABSTRACT
4.1 Introduction
This chapter describes finite difference methods often employed in coastal hydraulics in general, and highlights a three-dimensional hydrodynamic and pollutant transport numerical model with an orthogonal curvilinear coordinate in the horizontal direction and a sigma coordinate in the vertical direction. This model is based on the Princeton Ocean Model (POM). In this model a second moment turbulence closure sub-model is embedded, and the stratification caused by salinity and temperature is considered. Furthermore, in order to adapt to estuary locations where the flow pattern is complex, the horizontal time differencing is implicit with the use of a time-splitting method instead of the explicit method in POM. An efficient as well as simple open boundary condition is employed for pollutant transport in this mathematical model. This model is applied to the Pearl River estuary, which is the largest river system in South China with Hong Kong at the eastern side of its entrance. The distribution and transport of chemical oxygen demand (COD) in the Pearl River Estuary (PRE) is modelled. The computation is verified and calibrated with field measurement data. The computed results mimic the field data well, which show that the trans-boundary or interboundary 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 (PRDR), are quite strong.
