Program     Ocean Circulation, Ecosystem and Hypoxia around Hong Kong Waters       Poster Integration of catchment model and river delta network for improving simulation of fresh water discharges from outlets to estuary: a case study of Pearl River Delta and Estuary P-SPS4-13-S Xiao Feng* , The University of Hong Kong Ji Chen, The University of Hong Kong Zhongming Lu, Hong Kong University of Science and Technology Presenter Email: xfeng19@hku.hk Estuary waters are strongly affected by river fresh water discharges from the upstream basins; nevertheless, the fresh water discharges at an estuary is difficult to monitor due to the mixture of seawater intrusion to the river delta. This is a research gap in the world to rationally estimate the fresh water discharges into estuary. Moreover, it is of great importance to improve the simulation skills of discharges from outlets to estuary for study of coastal waters and better understanding of influence on estuary from river basin. In this study, the Pearl River estuary in South China is selected as the study area. Due to its complicated upstream river network and frequent human activities in the Pearl River delta, the estimation of discharges from the Pearl River delta to the estuary is rather challenging. SWAT (Soil and Water Assessment Tool) model is selected to simulate the terrestrial processes including streamflow, sediment and water quality in the Pearl River basin. Three scenarios for representing different diversion methods are used to test the influence of fresh water discharges on salinity of the estuary water. For validation, a coastal model is used to confirm the results from three scenarios through using salinity observations. This study will provide a method for the integrated study of river basin and estuary and can be applied in other regions in the world.