The scientific management of water resources requires an understanding of hydraulic and hydrologic processes. The need to understand and predict the impact of pollutant discharges or engineering works on the water environment has provided an impetus to the development of hydraulics in the past three decades. In recent years, environmental hydraulic problems have been assuming increasing importance in many Southeast Asian countries and cities, including China and Hong Kong. Volume 1 of a two-volume set, comprises the Proceedings of the 4th International Symposium on Environmental Hydraulics & the 14th Congress of Asia and Pacific Division, International Association of Hydraulic Engineering and Research held in December 2004 in Hong Kong. Volume 1 covers the selected papers presented at the 4th International Symposium, while Volume 2 features the advances outlined in papers from the 14th IAHR-APD Congress. Both volumes will be of interest to practitioners and researchers in sustainable water management and environmental science.