【作者】 李福林；

【导师】 王永吉； 夏东兴； 李培英；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2005， 博士

【摘要】 海水入侵是世界上海岸含水层中十分普遍和广泛分布的污染问题,认识、预测、防治以及含水层管理最好的途径便是进行监测和计算机的数值模拟。 本篇论文选择中国莱州湾东岸滨海平原作为研究区,通过研究,得到如下重要结论: (1)莱州湾东岸广泛分布沙质海岸地貌和第四系沉积物。受地质历史上两次海侵的影响,冲洪积物形成的陆相含水层延伸到海底很远的地方,这种海岸含水层结构和海岸环境给咸水向淡水区入侵提供了非常便利的通道。 (2)莱州市与山东省的的人均水资源量基本持平,地下淡水资源量较少。水资源供需平衡分析表明,即使南水北调工程完成后,现状的水资源供应也难以满足需求,水资源本身的缺乏和地下水超采是诱发海水入侵的关键因素。 (3)莱州市从上世纪70年代末便开始地下水位和水质的系统监测工作。多年的监测表明,海水入侵经历了初期发展、加速发展以及回退三个阶段。最近咸淡水界面自陆向海的回退的主要不是因为降水的增加和地下淡水开采量的减少,而是近岸海底含水层抽取咸水导致。 (4)莱州湾东岸的海底地下水分布在海底以下的第四系沉积物中,该类咸水储存在半承压含水层中,与储存在陆相含水层中的淡水具有较强的水力联系,并接受淡水的补给。现在大量的咸水被开采出来。研究表明,像PH值、密度、钠吸附比(SAR)等特征离子值,从陆向海遵循一定的分布规律。比如陆地含水层的高值硝酸盐也在海底地下水中有较好的反映。从陆向海,水化学类型逐渐从Cl-Ca.Na.Mg型向Cl-Na.Mg型和Cl-Na型转化。另一方面,离子强度(IS)和矿物相的饱和指数(SI)也遵循一定的分布规律,构成海岸带一般的水文地球化学演变模式。应用水化学方法可以较容易地确定海水入侵。 (5)除了水化学方法,物探技术包括垂向电阻率测深、瞬变电磁测深和激发极化方法也可用来监测海水入侵的发展。同时,包括Gamma射线和感应电导率测井的地球物理测井技术也被用作典型剖面的探测。通过探测曲线的解译,可以产生一系列的监测指标来确定咸淡水界面的动态变化。 本文通过大量的野外试验数据,获取了海水入侵监测的两类指标,一是由特征化学离子比值组成的水文地球化学指标,另外是由电阻率和Gamma值组成的地球物理指标。文中还给出了两类指标间的对应关系,并介绍了监测工作中应注意的一些事项。 (6)数值模拟是文中最重要的工作,首先利用小范围的抽水试验来验证水文地质参数,发现效果较好,因而该地区同类大量的抽水试验资料可以用作计算机模拟所需要的参数。更多还原

【Abstract】 Saltwater intrusion is arguably the most common and widespread contamination issue in the coastalaquifers around the world. The best means to understand, predict, and ameliorate saltwater intrusion,as well as to manage aquifers subject to saltwater intrusion, mainly involves monitoring andcomputer numerical simulation.This paper selected the east coast of Laizhou Bay of China as the key research area to study thistypical problem and draw some important conclusions.(l)The sandy coastal geomorphology and the Quaternary sediments are widely distributed in theeastern coast of Laizhou Bay. Due to two times transgression in the geology history, the aquiferformed by flood and alluvial deposits in the landward extends far away to the bottom of the sea.This kind of aquifer construction and coastal environment offers good conditions and veryconvenient path for saltwater intruding freshwater.(2) Water resources especially the groundwater in Laizhou city are very shortage compare to theaverage amount of Shandong province. By the analysis of water supply and demands, the presentwater resources can not meet the water requirements every year, even if the big project like WaterTransfer Project from South to North in China is completed in the future. Water resources lack andgroundwater over exploitation are the key induced factors of saltwater intrusion.(3)Groundwater table and quality monitoring work were done from 1979. For these many yearssaltwater intrusion passed through three periods of which includes primary development, fastincreasing and retreat. The recently retreat of the interface between the saltwater and the freshwaterfrom land to the coast is not due to the decrease of precipitation and the fresh groundwaterexploitation but caused by pumping of saltwater in the submarine aquifer.(4)The submarine groundwater along the eastern coast of Laizhou Bay is distributed in theQuaternary porous sediments below the shallow sea bed. This kind of submarine salt water storiedin the semi-confined aquifer has strong hydraulic connection with the landward groundwater storiedin the fresh water aquifer. Now large amounts of submarine groundwater discharge (SGD) are beingexploited which is mainly recharged by the inter-land groundwater. Studies show that the chemicalcharacteristic values such as PH, density, sodium absorption ratio (SAR) and rCl/rBr in thegroundwater follows the special rule from the land to the sea. In the mean time, the high value of Nitrates (NO3") in the land aquifer indicates the relative high value in the submarine groundwater. The hydrochemistry of groundwater from land to the sea is dominated by Cl-Ca.Na.Mg waters to Cl-Na.Mg waters and Cl-Na waters. In another hand, the ion strength (IS) and the mineral saturation index (SI) of the groundwater also follows the basic rule indicating the general model of hydrogeochemistry evolution in the coastal area. By using this method, saltwater can be delineated easily.(5) Except for the chemical methods, geophysical exploration techniques can also be used for saltwater intrusion monitoring which include the Vertical Electrical Sounding (VES), the Transient Electromagnetic Sounding (TES) and the Induced Polarization Sounding (IPS), etc. In the mean time, the geophysical logging including the Gamma ray and induced conductivity logging were used for typical profile detecting. With the interpretation of these detecting curves, a series of monitoring indexes are produced to determine the dynamic variation of salt-freshwater interface. Based on analysis of lots of measured field data, this paper gained two kinds of indexes to monitor saltwater intrusion. One is hydrogeochemical monitoring index mainly composed of characteristic chemical ion ratio, and the other one is geophysical exploration monitoring index mainly composed of resistivity and Gamma values. And then elaborated the relationship between the two kinds of indexes and introduced some problems must be paid attention to in the monitoring work. (6)The numerical simulation is the most important work in this paper. Pumping test were done in a small area to validate the hydrogeology parameters and it is found result is very good and lots of parameters obtained by this kind of pumping test in this research area can be used for the computer simulation.(7) FeFlow is a finite element based model with a wide selection of numerical solvers for performing complex 2D and 3D steady-state or transient groundwater flow and contaminant transport modeling. Saltwater intrusion in the confined aquifer (Henry problem) and unconfined aquifer (Huyakom problem) which are the classical issues were simulated by using the FeFlow software. It is found that the simulated results are similar with others in the publications. In the meantime, the migration of salt-fresh water interface drew by the groundwater funnel and the effect of subsurface barrier for saltwater prevention were also simulated. It is obviously seen that the software can solve this kind of density-dependent flow and mass transport problem.(8) 3D transient flow and mass transport model were set up to simulate the development ofsaltwater intrusion of Laizhou from 1998 to 2003. It is found that the computed results fit to the truedata well. Groundwater funnel are found in the submarine aquifer near the coastline. Thoughgroundwater table declined in the recent years, the salt-freshwater interface moved from the inlandto the coastline.(9)Saltwater intrusion has good relationship with the precipitation, groundwater and saltwaterdischarge. Using artificial neuron net model can analog and predict the area variation of saltwaterintrusion along with the three factors. If it encounters several continuous dry seasons in the futureand in the mean time keeping the small scale of groundwater exploitation just like the present year,the saltwater will not intrude to the inland because of the submarine saltwater pumping, but ifincreasing the amount of groundwater pumping along the coastal area, the saltwater intrusion wouldoccur from the beginning.(10)Much success of saltwater prevention is achieved in the area of coastal aquifer and phreaticaquifer. New types of prevention engineering have being constructed in the coastal area fromseveral years ago, of which including land-filling tidal prevention project, subsurface barrier projectin the estuary and submarine salty water exploration project for breed aquatics. Whether theseprojects do harm to the coastal environment needs more constant monitoring and forecastingresearch.Using the advanced international theory and technique of coastal and river ecosystem restoration,the ecological prevention theory should be the guide of the proper way to prevent saltwaterintrusion, but much work should be done to make the theory perfect and make progress with theengineering technology in the future.更多还原