The Status, Mechanism And Numerical Simulation Of Seawater Intrusion In The Kiaochow Bay Area

Within all variety of geological hazards which exist in Kiaochow Bay region, seawater intrusion is of the largest scale, the most influential and the most serious hazard losses. According to the study of the seawater intrusion in Kiaochow Bay region,there will be practical significance in the coming implementation of Kiaochow Bay's development strategy , economy and social sustainable development in Qingdao city, it also provides geological evidences for the urban planning, construction, management and hazard prevention and mitigation, Profiting and avoiding loss and so on, it also conducive to the rational development and protection of regional water resources, geological resources.The achievements ,which include geological survey data, mechanism of seawater intrusion and evolution rules and so on, have academic reference meaning for this region and other ralated areas.Since early March 2008 to the end of December 2008 ,according to the study of the status of seawater intrusion in Kiaochow Bay region in the scale 1:25000 ,we get the newest seawater intrusion data which corresponds to a hydrological year's. With the content of Cl- 200mg/L,250mg/L,300mg/L in groundwater as main index we divide Kiaochow Bay region into four parts:non-seawater intrusion region,the slight one,the more serious one and the severe one.And we can conclude that the most serious seawater intrusion region is the river estuary of Dagu river,Baisha river and Yang river and Xin'an region of Huang island, it will be gradually less serious in backland andtwo banks of rivers. According to the disaster loss assessment of the seawater intrusion region whose Cl- content is more than 250mg/L in groundwater, we estimate that the direct economic loss is about 193050 thousand yuan.Combined with expert clustering and fuzzy mathematics comprehensive evaluation method ,we make comprehensive evaluation to the risk of the seawater intrusion which happens in the Kiaochow Bay coastal region , which the four evaluation factors are Cl-,sodium adsorption ratio(SAR),SO42+ and Mg2+,confirm their weight values separately, classify the risk of seawater intrusion with emphasis on risk, medium risk, light risk and risk-free.Based on this,we make use of GM(1,1)grey model theory to predict the risk of seawater intrusion with average rate is 8.7m/a for many years, which conclude that the seawater intrusion area in 2015 in every region will be increased by 9.6km2,5.7km2,3.6km2,2.0km2 separately compared to 2008, the seawater intrusion boundaryies continue to be the trend of moving to freshwater area.By analyzing the space-time dynamic change, ion content change of stratum structure ,rainfall and groundwater level ,chemical characteristics evolution and human development activities and other factors, and emphasizing on the analysis of the Cl-content change in seawater intrusion and and its physical characteristics ,we conclude that the mechanism,mode and style of seawater intrusion.The well permeable gravel layer provides access for seawater intrusion;Under natural conditions, groundwater discharge to the basin , both sides of the transition zone between seawater and groundwater maintain a dynamic balance, both sides of the state of water are in a gradual change;The economic development, unreasonable intercept water storage, drought and dry, water quality deterioration and so on forced the human exploitation of groundwater has intensified, leading to the emergence and development of groundwater cone of depression and damaged natural water equilibrium and the water and salt movement,thus groundwater movement of funnel around to the center of it appear , and cause seawater to move to the inland and reverse osmosis will happen along the permeable layer, anti-recharge groundwater, resulting in seawater intrusion.Start with deep seawater intrusion began to move forward in the process of development from bottom to top. The main type of seawater intrusion of Kiaochow Bay region is exploitation and intrusion.Aimed at the seawater intrusion problems in Kiaochow Bay region ,taking Baisha downstream as the example,based on the the water medium conditions ,water flow conditions and boundary conditions, we analyze water level, water quality dynamic data, generalized aquifer system boundaries, internal structure, then establish the concept models of the hydrogeology, combined with the pumping and dispersion testing Nvgu to determine hydrogeological parameters, the application of FEFLOW simulation system has been simulated.To June 1, 2003 -2008 year May 31 as the basis for long-term observational data to identify a better validation curve fitting.Select from November 2008 to October 2013 in a total of 5 years for seawater intrusion prediction, and generates a Cl-ion content contours.We can see that seawater intrusion in the dry years, heavier, Cl-enrichment was obvious.Baisha downstream Zhao village under the action of seawater intrusion , Cl - content expand the direction to the inland ;Due to much agriculture and a large quantity of groundwater extraction in Ink river in the northeast, Cl– content is much higher.In accordance with the method above, numerical simulation of other seawater intrusion areas are made, and combine Cl-ion content equivalent line into MapGIS to get the seawater intrusion prediction contour map of Kiaochow Bay region.For prevention and control seawater intrusion hazard, in addition to the optimization of groundwater cone of depression of groundwater development and management of projects, there are also the construction of cutoff wall, river management, rational development of coastal resources, ecological improvement and other measures, as well as the rational use of water resources, water pollution control, to saving water and so on. Take White Shahe downstream for example,we design three mining programs, 151 days of continuous mining; program one is that mining resource is 50000m3/d, program two is that when mining resource is 42000m3/d the water level drawdown is too large; program three is that when mining resource is 30000m3/d to meet the water level drawdown of no more than allowing the requirements of the funnel center's water level drop as deep as 4.1m,> 4m drawdown area of 0.188km2,> 3m drawdown area of 5.75km2,> 2m the area of water level drawdown To 19.50km2.The designed Baisha downstream recharge project, the average recharge volume 52540 m3/d in high-flow period, the total annual recharge is 4.83368 million m3; two consecutive dry (annual rainfall 420mm) 1 abundant year (annual rainfall 880mm ) water levels pridiction shows, in addition to exploitation of the funnel near the center of a 1 ~ 2m deep down, the water level has basically returned to the original level, indicating recharge is feasible. In fianl,we propose the comprehensive management programs of Kiaochow Bay seawater intrusion , including the construction of cutoff wall, recharge, soil improvement and other targeted measures, and the establishment of Kiaochow Bay region groundwater monitoring system.