Risk Assessment Of Seawater Intrusion Disaster In The LaiZhou Bay Based On GIS

Seawater Intrusion is that seawater or saltwater intrude into the continent along the aquifer. Under the effects of the natural and artificial factors, the hydrodynamic conditions of aquifer in the coastal area has been changed,which break the equilibrium between the seawater and the freshwater, hence the salt-fresh interface moves on the continent. Because of the arid climate, the low-lying terrain, widespread Quaternary unconsolidated sediments, high salinity of groundwater and excessive exploitation of groundwater resources by human being, Laizhou Bay is the most typical and serious region suffering from the geo-hazard of the seawater intrusion in China.This paper based on the periodic data from field survey from Jun.2007 to Jun. 2009, analyzed the dynamic changes of groundwater level and the distribution of Chloride concentration and mineralization and made the distribution map of groundwater level and mineralization.The actuality assessment indexes are conceived through choosing the factors of concentration of Cl" and mineralization. Spatial analysis of ArcGIS software is applied involving in the evaluation process expressing. The result shows that the area of seawater intrusion in study region is nearly 4392km2, and the serious intrusion area is 3092 km2.The space and time distributing trend of seawater intrusion in Laizhou Bay and the cause of formation are analyzed detailedly. The seawater intrusion disaster is mainly occurred in the alluvial-marine plain where lying in the north of boundary of the fresh groundwater and the altitude is between 0～10m and in the south of boundary of the fresh groundwater where the groundwater level is below the sea level. The time distributing trend is not significant in annual period. The seawater intrusion is caused both by nature and human being, the Quaternary unconsolidated sediments, the underground saltwater the low-lying terrain and the arid climate are the environmental background and the over exploitation of ground is the dynamic conditions.The relationship of geological, geomorphological and hydrogeological condition of Laizhou Bay with seawater intrusion is analyzed based on the summary of them. Taking into account of human activities on sea water intrusion disasters, and using the AHP model, the risk assessment indexes of seawater intrusion is conceived by choosing factors such as ground elevation, sediment types, mineralization, groundwater level well density, population density, unit area of cultivated land, unit area of GDP, urbanization and regional groundwater water accounts for the proportion of total water consumption.Based on the theory of the nature hazard risk assessment and the actual situation in The Laizhou Bay, the seawater risk assessment indexes are divided into:hazard assessment, vulnerability assessment and protection & recovery capability assessment in this paper. The seawater risk assessment by means of GIS automatically was overlaid on the assessment results of the three indexes:hazard, vulnerability and response & recovery capability, which was classed into high, slight high, medium, slight low and low. The result shows that the high-risk area is accounted for more than 40% of the evaluation area and the boundary between the more dangerous and less dangerous zone is the line of Shouguang-Hanting-Changyi-Xinhe. The widely distributed Quaternary unconsolidated sediments is main source and path of the seawater intrusion disaster, and pumping the underground freshwater and saline groundwater is the induced conditions of the seawater intrusion disaster.Based on the .NET and ArcGIS Engine platform, the risk assessment of seawater intrusion disaster system is developed by using monitoring data and basic information of seawater intrusion in Laizhou Bay. The system can store and mange the monitoring data and evaluate the risk of seawater intrusion conveniently, which provide technical support for forecasting and prevention of seawater intrusion in Laizhou Bay.