Salt water intrusion analysis and trend forecast in the coastal plain of the Laizhou Bay

Taking Guangrao county of Shandong Province as an example, authors expatiate geological background for salt and fresh water formation, and formation and evolvement for transition-zone of salt and fresh water, analyze the history and actuality of salt water intrusion arisen by extensive groundwater exploitation, forecast intrusion trend for salty water using indeterminacy model method, and point out measures and proposition to control salty water intrusion. Main conclusions are: 1) Groundwater quantity had the characteristics of horizontal zoning and vertical zoning; 2) Salt and fresh water exchange zone was on moving state in geologic epoch. Since the middle of medio-pleistocene, several times transgression have happened, and the third transgression had the most wide influence. The distance of paleocoastline was 10 to 20 kilometers away from current transition-zone of salt and fresh water. During the span of 20-40 thousand years geological epoch prior to the period when human cosmically exploited and utilized groundwater, brackish water in primary saline aquifer desalted gradually, and formed fresh water zone, which was about 10-20 km in length. 3) From the 1970s, fresh groundwater was exploited in a large scale in this area, and the level of fresh groundwater continuously dropped. Hydrodynamic equilibrium between fresh and salt water have been broken. The salty groundwater in the north area intruded into south area, so a lot of geo-environmental problems appeared, such as fresh water salinization, well abandonment and so on. The forecast result shows: fresh-salt water interface would move toward the south at the speed of 240m/y if without controlling measures. 4) Artificial recharge, building fresh-water curtain and reducing exploitation in fresh water areas were efficient measures to avoid salty water intrusion.