Empirical Studies On Risk Assessment System Of Accidental Water Pollution Events In City's Source Water Area

Presently, most of domestic cities are under progress of rapid urbanization, meanwhile the conflicts between source water protection and city development are increasingly arising, and accidental pollution of source water is becoming as one of the focusing issues. As an opening water body, the upper watershed of Huangpu River would serve as No.1 source water area of Shanghai for a long time. However, the source water area has suffered from various pollutions over past few decades, especially including accidental pollution events. According to the current situation and future development, ship's oil spill accident is expected to become one of the most dominant risk events threatening the safety of the source water area of Huangpu River. Therefore, it is meaningful to carry out empirical studies on the risk management theory and assessment method in terms of the accidental pollution events in source water area.The paper reviews both domestic and foreign researches regarding accidental water pollution, especially for the subject of accidental water pollution event in source water area. From the perspective of risk assessment, 7 typical risk sources causing accidental pollution events in source water area are identified and also be classified according to locations, polluting approaches and diffusing modes in the paper. Additionally, the major accidental water pollution events occurred in source water areas in China during the last 20 years are summarized and analyzed. Especially, characteristics of the accidental water pollution event in water source area are analyzed with the example of ship's oil spill and leakage, and the detailed characteristics are including uncertainty of risk sources, vulnerability of risk acceptor, time sequence of risk process, emergency of risk assessment and complexity of emergency action.On the basis of traditional system of environmental risk assessment, the paper presents the "Time Sequence Assessment Systems" specially for assessing the risk of accidental water pollution event in water source area. According to "Time Sequence Assessment Systems", the event is divided into three time sections, which are respectively called as "Before Occurrence Section", "Under Occurrence Section" and "After Occurrence Section", and each section correspondingly matches up with "Risk Forecast Assessment", "Risk Emergency Assessment" and "Risk Impact Assessment". Concretely, "Risk Forecast Assessment" focuses on evaluating the "accident risk", "Risk Emergency Assessment" focuses on evaluating the "impact to intake", and "Risk Impact Assessment" focuses on evaluating the "risk to water and health".Supported by the project of National Natural Science Founding: Empirical Studies on Environmental Safety in Urban Water Source area and Emergency Mechanism for Accidental Pollution Events CNo.70403005) , and the project of Key Scientific Issue of Shanghai Science Committee: Research on Early-warning System for Accidental Water Pollution Events in Huangpu River and Decision-making Supporting Systems of Watercourse (04dzl2031), .the paper conducts "Risk Forecast Assessment" and "Risk Emergency Assessment" with the object of source water area in Huangpu River.The paper conducts risk identification and risk analysis on the accidental water pollution event in Huangpu River, and eventually has the following major conclusions: ship's fuel oil leakage is the major risk event; Wujing section is the highest risk area; the most reliable event is the ship's fuel oil leaking in Wujing section under the conditions of flood tide and south-east wind.