The Evaluation And Forecast Study Of Seawater Intrusion Disaster Risk Degree In Weihai City

Seawater intrusion was the phenomena that recharging seawater erodes the fresh groundwater because of the fresh water level dropping, and the ocean geologic disaster which was caused by natural conditions and the human activities. With the continuous advancement of the society, the fast economic development and the rapid growth of the population make the underground water requirement incremental and the extent continuous increasing. Since 1980s, the large groundwater exploitation makes the water level drop sharply and causes seawater intrusion happen frequently in coastal cities in our country, which affects the groundwater resource badly and restricts the society development. Recent years, seawater intrusion attracts the scholars'attentions of home and abroad and was listed to be the main contents of the seaboard geologic disaster evaluating because of the deep harmful extent and wide areas affecting. There were already lots of researches on the causes of the seawater intrusion, forming mechanism and intrusion status quo made by the researchers home and abroad. From their researches, the seawater intrusion disaster risk degree was not only a simply physical process of seawater intruding groundwater but a complex synthesis analysis progress of the topographical polygenetic information.In the paper, the author introduces the theory base and the development status quo of the seawater intrusion, the natural conditions, humanitarian geographical conditions and society economic situations of Weihai city. The Topsis method and GIS technology were used on the evaluation and forecast researches of the seawater intrusion disaster risk extent of three cities and one district of Weihai city. The evaluation includes four targets of Weihai city, such as geographic condition, geologic condition, climatic condition and human condition, and it draws the conclusion that the most fragile regions of the seawater intrusion disaster risk degree in Weihai city were 357.395km~2, which were mainly the coastal such as Zhangcun town of Hi-tech Industrial Development District, Tiancun town, Haobo town of Huancui District, the coastal of Gangxi town, Chengshanwei, Lidao town, coastal of Yatou town which were in Rongcheng city, Zetou town, the coastal of Xiaguan town which were in Wendeng city, Kou town, the coastal of White Sands which were in Rushan city and so on. The intrusion area of above three cities and one district account for 95.023km~2,78.576 km~2,82.72km~2,and 101.076km~2 respectively, among which ,the speed increase most fast in Huancui District by the speed of 10.07 km~2,while the average speed of Weihai city was 35.75 km~2,the seawater intrusion disaster disk degree was much higher, Therefore, we should reinforce the prevention and control and forecasting against the seawater intrusion of these areas for the farther development of it.According to the GDP statistical data and the consuming amount of water per GDP unit of Weihai city and depending on the time series regression analysis, the forecasting concludes the GDP data and consuming amount of water of 2015 and 2020, and then risk degree which were about the year of 2015 and 2020 of seawater intrusion disaster of Weihai city. The forecasting concludes that the most weak regions of the seawater intrusion risk degree will be 602.4km~2, which was 245km~2 more than now under the conditions that the geographic condition, geologic conditions, climate condition steady correspondingly, the consuming amount of water per GDP unit not changing and no outside water resources. Among which, the areas of the most fragile regions of the seawater intrusion disaster risk degree in Huancui District,Wendeng City,Rongcheng City and Rushan City were 19.313 km~2,145.51 km~2,190.933 km~2,146.645 km~2 respectively. Until 2020, it will be 1114.6km~2, and the most fragile regions areas were 301.717 km~2 , 165.678km~2 , 490.656km~2 156.527km~2 respectively in three cities and one district. From the forecasting results, the speed of the seawater intrusion will increase quickly by the increasing rate of 75.72 km~2 per year. If no prevention and control, it will bring serious influence. In the end of the paper, the corresponding defending measures and suggestions were given out according to the evaluation and the forecasting conclusions which supply the decision-making and foundation for the management of the groundwater resource , the environment protection and the region programming.