THE PATTERN OF SEAWATER INTRUSION IN THE LONGKOU-LAIZHOU AREA
Xue Yuqun, Xie Chunhong, Wu Jichun, (Nanjing University) Liu Peimin, Wang Jianji, diang Qingpo, (Office of the Water Resources of Longkou, Shandong) Shi Hongwen and Ning Peihai (Office of Water Resources of Laizhou, Shandong)
The present situation and features of the seawater intrusion (or encroachment), the hydrochemical characteristics of groundwater, the features of saline water-fresh water interface and its movement in the Longkou-Laizhou area, Shandong Province, are studied. In 1989, the area of seawater intrusion is 238.3 km~2 in Laizhou (31.5% of its total plain area) and 83.7km~2 in Longkou (18.6% of its total plain area) respectively. The seawater intrusion developed from a point to a large scale. Restricted by geological conditions, the forms of seawater intrusion are variable. The velocity of seawater intrusion varied from place to place. There are close connections between the area of seawater intrusion and the area whose groundwater level is below the sea level due to overpumping. The real distribution of seawater intrusion is connected with the area where strong, intensive pumping exists. The existence of lagoonal or marine argillaceous sediments in coastal zones accelerated the enrichment of Cl~- in groundwater. In seawater intrusion areas there is a broad transition zone with a width of 1.5—6.0 km between saline and fresh water. The groundwater in the transition zone is by no means a simple mixture of fresh water and saline water. The cation-exchange played an important role, which caused the decrease of Na~+ and the concentration of Ca~(2+) in the transition zone. There exist two types of saline waterfresh water interface which is related to the pomp discharge and the distribution of pumping wells. The interface formed at the continental side nor far from the area where strong, intensive pumping is carried out, and the seawater intrusion stopped there. Finally, this paper discusses the causes of the seawater intrusion and effective measures to prevent and control seawater intrusion.