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Water Quality Modelling

 

 

A. Summary of activities

 

Besides the development of conventional 3-dimensional current models and dispersion & diffusion models based on the eddy viscosity concept to predict the transport of pollutants by currents, the Group is conducting research on transport processes characterized by small pollutant clouds with a scale smaller than the largest scale of the water motion.  The determination of the characteristics of these processes in Hong Kong waters is important for the assessment of the far field environmental impact before the implementation of the Strategic Disposal Scheme.  Since there are many land reclamation and dredging projects in Hong Kong, the Group has developed a model to predict the transport of particle clouds in coastal waters.  Laboratory experiments have been conducted to verify the numerical model.  The Group has studied the eutrophication problem in Hong Kong.  In addition, an expert system for the selection and manipulation of flow and water quality models is now under development.  Since the Pearl River delta region is an area with great potential for further economic development, the Group is now carrying out a systematic investigation of the hydraulics and water quality of the Pearl River estuary, including the use of satellite remote sensing technique and artificial neural networks.  The accumulation of contaminants in sediments of the Pearl River estuary is also actively studied.

 

 

B. Representative projects

 

Two-layer eutrophication numerical model for Tolo Harbour, Hong Kong

 

The objective of this project is to develop a two-layer, tidally averaged model which can quantitatively predict the trophic status of the Tolo Harbour both in the summer and winter conditions.  The differences in surface and bottom water temperature distributions during the summer season have resulted in temperature stratification in the vertical water column in Tolo Harbour.

 

Expert system for selection and manipulation of numerical models on flow and water quality in coastal waters

 

The objective is to develop design aids and educational tools for the numerical simulation of flow and water quality in coastal waters, using recent technologies of computer aided design and expert system.  The expert system under development is intended for use by hydraulic and environmental engineers who have only basic knowledge of flow and water quality modelling.

 

Large eddy simulation of non-Fickian diffusion in coastal waters

 

The objective is to develop a three-dimensional model using the large eddy simulation technique for inhomogeneous, anisotropic turbulent flow and dispersion in coastal waters.

 

Dispersion of unsorted sediment cloud in crossflow

 

The objective is to obtain a fundamental understanding of the phenomenon of dispersion of particle cloud in the presence of crossflow and hence to develop a well verified numerical model for simulating the near field mixing of unsorted particle cloud in both laboratory and field situations.

 

Three-dimensional modelling of hydrodynamics and sediment transport with parallel algorithm

 

The objective is to develop an efficient and accurate method for three-dimensional hydrodynamic and sediment transport computations.  The numerical model is parallelized using the domain decomposition, the master-slave paradigm and the grid renumbering scheme to achieve an efficient parallel algorithm.

 

Sediment transport by waves and tidal currents in the Pearl River estuary

 

The objective is to develop a three-dimensional finite element model for the Pearl River estuary to study the transport and the fate of marine sediments under the combined action of wave and current.

 

Satellite remote sensing for water quality monitoring

 

This is a joint project with the Department of Land Surveying and Geo-informatics of the University.  The objective is to investigate the seasonal changes of marine water quality through the analysis of satellite images.  The assessment and prediction capabilities can be greatly enhanced if remote sensing and computer modelling are used together.

 

Adsorption and desorption of heavy metals on/from Pearl River estuary sediments.

 

This is a joint project with the South China Sea Institute of Oceanology, Chinese Academy of Sciences.  The objective is to study the accumulation of heavy metals and their adsorption/desorption rates by analysing core samples collected at various locations in the Pearl River estuary.  A water-sediment-metal interaction model will be developed for water quality monitoring and assessment in the Pearl River Estuary.

 

Water quality prediction using artificial neural networks

 

This project will be carried out in collaboration with the Environmental Water Management Research Centre at University of Wales, Cardiff, U.K.  The objective is to develop an integrated model combining artificial neural networks with process based deterministic models to give more accurate and efficient predictions of water quality in the Pearl River estuary.

 

C. Selected recent output

Chau, K.W. and Jin, H.S., Eutrophication model for a coastal bay in Hong Kong, Journal of Environmental Engineering, ASCE, Vol. 124, No. 7, pp. 628-638, 1998. 

Jin, Haisheng, Egashira, Shinji and Chau, K.W., Carbon to chlorophyll-a ratio in modeling long-term eutrophication phenomena, Water Science & Technology, Vol. 38, No. 11, pp. 227-235, 1998.  

Chau, K.W. and Jin, H.S., Depth-averaged, two-dimensional eutrophication modelling for Tolo Harbour, Hong Kong, Environmental Modeling and Assessment, Vol. 4, pp. 189-199, 1999. 

Chau, K.W., Transverse Mixing Coefficient Measurements in an Open Rectangular Channel, Advances in Environmental Research, Vol. 4, No. 4, pp. 287-294, 2000. 

Chau, K.W. and Jiang, Y.W., 3D Numerical Model for Pearl River Estuary, Journal of Hydraulic Engineering, ASCE, Volume 127, No. 1, pp. 72-82, 2001. 

Chau, K.W. and Chen, W., A Fifth Generation Numerical Modelling System in Coastal Zone, Applied Mathematical Modelling. (in press) 

Li, C.W. and Wang, J.H., "Large eddy simulation of free surface shallow water flow", International Journal for Numerical Methods in Fluid, vol. 34, 1, 31-46, 2000 

Li, C.W. and Ma, F.X., "3D numerical simulation of ambient discharge of buoyant water", Applied Mathematical Modelling, vol. 25, 5, 375-384, 2001 

Li, C.W. and Gu, J., "3d layered-integrated modelling of mass exchange in semi-enclosed water bodies", Journal of Hydraulic Research, in press. 

Li, C.W. and Ma, F.X., "3d numerical simulation of deposition patterns due to sand disposal in flowing water", Journal of Hydraulic Engineering, American Society for Civil Engineers,  vol. 127, 3, 209-218, 2001 

Li, C.W. and Lin, P., "A numerical study of three-dimensional wave interaction with a rectangular pile", Ocean Engineering, in press. 

Li, Y.S. and Zhan, J.M., A 3-dimensional finite element model for stratified coastal seas", Journal of Hydraulic Engineering, ASCE, Vol. 124, pp.699-703, 1998.

Wai, O. W. H., Xiong, Y. S., O'Neil, S. and Bedford, K. (2001). "Parameter estimation for suspended sediment transport processes under random waves." Science of the Total Environment, Vol. 266 (1-3), pg. 49-59. 

Wai, O. W. H. (2001). "Evaluation of the Kwun Tong PTW's Flow Measurement System." Final Report, Government of Hong Kong, Drainage Services Department, 26 pgs. 

Huang, S. L., Wai, O. and Li, Y. S. (2000). “Determination of Cadmium Ion Desorption from Non-uniform Sediment Particles.” Toxicological and Environmental Chemistry. (Accepted). 

Wai, O. and Lu, Q. (2000). “An Efficient Parallel Model for Coastal Transport Process Simulation.” Advances in Water Resources, Vol. 23(7), pg. 747-764. 

Wai, O. and Lu, Q. (1999). “Gradient-Adaptive-Sigma (GAS) Grid for 3D Mass Transport Modeling.” Journal of Hydraulic Engineering, ASCE, Vol. 125(2), pg. 141-151. 

Chen, Y., Wai, O., Y. S., Li and Lu, Q. (1999). “Three-Dimensional Numerical Modeling of Cohesive Sediment Transport by Tidal Current in Pearl River Estuary.” International Journal of Sediment Research, Vol. 14(2). pg. 107-123.  

Wai, O. W. H. (1999). "Siltation module calibration and validation service." Final Report, Government of Hong Kong, Civil Engineering Department, Civil Engineering Office, 101 pgs.  

Wai, O., Chen, Y. C., Lu, Q., and Li, Y. S. (1998). “A Multi-Layer Finite Element Formulation for Suspended Sediment Transport in Tidal Flows.” International Journal of Computational Fluid Dynamics, Gordon and Breach Science Pub., Vol. 9, pg. 137-149. 

Lu, Q. and Wai, O. (1998). "Three-Dimensional Coastal Hydrodynamic Computations with An Efficient Splitting Method." International Journal of Numerical Methods in Fluids, Vol. 26, pg. 771-789. 

Wai, O. W. H. and Huang, Suiliang (1998). "A review of heavy metal pollution in the Pearl River estuary." Proceedings of the Workshop on Hydraulics of the Pearl River Estuary, ed. Li, Y. S., The Hong Kong Polytechnic University, 123-136.

 

 

D.  Contact person

 

Dr. C. W. Li , Associate Professor

Tel:(852)  2766 6043, Fax: (852) 2334 6389, Email: cecwli@polyu.edu.hk

 

 

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Last modified: 2001/03/23