Survey And Research On Seawater Intrusion In The Yandaihe Plain Of Qinhuangdao City

The Yandaihe plain belongs to the pre-mountain Alluvial-proluvial plain andsea-proluvial plain. In the late 1970's, the groundwater table had been declining dueto the groundwater exploitation and years' drought. Consequently the negative valuezone of the groundwater table was formed in coastal areas, which leads to seawaterintrusion and seriously affects the economy and environment in the coastal region.In order to investigate the regularity of seawater intrusion and ease down thistrend in Yangdaihe plain, The PhD dissertation analyzes the distribution of seawaterintrusion, the characteristic of transition zone and intrusion types on the basis of thesurvey during 2002-2004 and previous research data. In the dissertation, the seawaterintrusion is divided into two zones according to the intrusion feature—eastern riverzone and western depression cones zone. The western is the typical intrusion zoneaffected by depression cones whose intrusion is along the aquifer, while in the easternzone, the tidal intrusion combines with seasonal intrusion, and the intrusion sources ofseawater include tide, seawater intrusion along aquifers and seawater remnants. Theeastern intrusion zone moves slowly towards west due to the depression cones in thewest, and the moving speed is 200m/yr.On the basis of analyzing the characteristic of seawater intrusion in theYangdaihe plain, the author summarize intrusion regularity, analyze its factors whichaffect the seawater , and conclude that the primary factor is anthropogenic influenceincluding the groundwater extra-exploitation, sluice at the upriver, et al. And thesecondary factor is natural influence including drought for years, the frequent stormand the penetrable stratigraphy.By the numerical simulation, the author works out that the groundwaterexploitation valve is about 3 × 109m3, but the current situation is underextra-exploitation. Under the same exploitation condition, the extension of seawaterintrusion in the east is greater than that of in the west. Thus the groundwaterexploitation should be strictly limited in the east and gradually reduced in the west.Furthermore, the rubber-dam project and artificial recharge source project areevaluated separately by the numerical simulation. The results demonstrate that notonly the quality of groundwater will be improved, but also the extension of seawaterintrusion will be reduced by means of previous scheme. Meanwhile, the investment oftwo projects is low and it has little influence on environment. Therefore the twoschemes are feasible to reduce the extension of seawater intrusion in Yangdaihe plain.