Abstract: EDSS is a comprehensive software system for water quality management in tidal river networks in general and for the Pearl River Delta in specific. Its purpose is to provide a practical tool which could assist government agencies in decision making for the efficient management of water resources in terms of both quantity and quality. By combining the capabilities of geographical information system(GIS), database management system(DBMS), model management system(MMS) and expert system, EDSS integrates relevant environmental databases, hydrodynamic and water quality models, optimization procedures, knowledge based expert systems, and environmental regulations so that data, models, human intuitions, expertise, and policies can be used in a seamless manner. This paper first outlines the basic concepts and philosophy adopted in developing EDSS, the system architecture, design features, implementation techniques and facilities provided. Thereafter, the core part of the system-the hydrodynamic and water quality models are described briefly. The final contribution in this paper describes the application of EDSS to the Pearl River Delta, which has the most complicated tidal river network patterns as well as the fastest economic development in the world. Examples are given of the real world problems that can be addressed using the system. These include trans boundary water pollution analysis, regional drinking water take up site selection, screening of important polluters, environmental impact assessment, and water quality zoning. It is illustrated that EDSS can provide efficient and scientific analytical tools for planning and decision making purposes in the age of information.

Key words: EDSS, GIS, DBMS, hydrodynamic and water quality models, water quality zoning, tidal river networks, the Pearl River Delta