【作者】 杨利超；

【导师】 王旭升；

【作者基本信息】 中国地质大学（北京） ， 地下水科学与工程， 2011， 硕士

【摘要】 珠江三角洲地下水资源潜力和地下水环境问题日益受到重视,但是区域地下水流场和水化学演变特征的研究程度较低。该地区濒临南海,第四系含水层随着三角洲沉积条件的变化,经历了多次海进海退的作用,形成了以底部砂砾石层为强透水层,以淤泥质粘土夹砂为弱透水盖层的含水层体系,地下水的矿化度总体较高。在此背景下,研究了珠江三角洲区域地下水流场和淡水驱替盐分运移的问题。通过综合考虑区域地质构造以及第四系沉积特征,依据300多个钻孔数据,构建了珠江三角洲第四系含水层空间结构模型:取沉积相和地层年代划分为6层;取水文地质属性划分为4层。其中,最底部的砂砾石层是有供水意义的含水层,其粘性土覆盖层中砂体的分布与古河道有关。运用微水试验分析方法对粘性土中的抽水试验进行了研究,获得了粘性土的渗透系数。结果表明,研究区粘性土的渗透系数非常小,数量级为10^-410^-5 m/d。根据珠江三角洲古河道的发育特征,取自上游地区到达海岛的长约180 km的投影剖面,绘制了垂向上的含水层结构,作为剖面二维分析的基础。以MODFLOW为模拟工具,对投影剖面上的地下水流场和盐分运移进行了数值模拟,发现存在多级流动系统,地表淡水1000年的驱替最大深度约20 m。多层结构的准三维地下水流模拟表明,区域地下水主要受地表水控制,水力梯度较小,淡水在砂砾石层的水平驱替速率最大可以达到66 km/万年。对于古河道的影响、沉积历史在建模过程中的考虑、海底含水层的处理等问题,进行了专门的讨论。更多还原

【Abstract】 The potential groundwater resources and associated environmental issues in Pearl River Delta attract increasingly attention. However, the knowledge of regional groundwater flow and evolution patterns of groundwater chemistry are still weak. The studied area is located nearby South China Sea. The Quaternary sediments have experienced several times between transgression and regression with the changes of sea level. As a result, the Pearl River Delta deposits form an aquifer system with a high permeable confined aquifer composed of gravel sand at the bottom and a low permeable confining unit composed of silty clay, silty sand and sand interbeds. In addition, salinity of groundwater is generally high. On the basis of this background, the patterns of regional groundwater flow and salt transport driven by freshwater infiltration in Pearl River Delta are studied.According to the regional geological structure and Quaternary sedimentary characteristics as well as more than 300 boreholes data, a spatial structure model of the aquifer system is built up. The strata can be divided into 6 layers in considering of sedimentary facies and chronological age. However, the sediments can be classified into 4 layers for numerical modeling in considering of their hydrogeological properties. In these layers, only the gravel sand layer at the bottom has significant for water supply. Distribution of sands in its clayey confining unit is controlled by paleo-rivers. The hydraulic conductivity of clay is obtained through investigation of pumping test data with slug-test analysis method. It is indicated that the hydraulic conductivity of silt is small, with an magnitude of 10^-410^-5 m/d. Along a main direction of paleo-river in Pearl River Delta, a typical reference profile from the upper-stream to a island in the sea is selected and drawn with aquifer systems. The length of the profile is about 180 km. The steady state groundwater flow and salt transport on the profile is simulated with MODFLOW, it is found that multi-flow systems develop on the profile and the maximum penetrating depth of fresh water is 20 m with respect to 1000-years transport. The multi-layers quasi-three-dimensional modeling of regional groundwater flow shows a pattern of flow filed that dominated by distribution of surface water. Hydraulic gradient in horizontal is small. The fresh water front can moves in the gravel sand aquifer to a maximum distance of 66 km, in ten thousand years, from its source area.At last, the impacts of paleo-river channels, the role of sedimentary history in the modeling process and the treatment of submarine aquifer are discussed.更多还原