潜流带水动力特性及污染物质输移过程研究

Groundwater- surface water interaction is the main character of hyporheic zone. It controls the mass and energy transfer in this area. The containments will stay in the hyporheic zone because of the low hydrodynamics of groundwater and adsorption by the sediments. In this application, the research will work on three aspects as follows: First, the water flume experiments and numerical simulation based on large eddy wimulation coupling with groundwater and surface water will be carried out. The study will focused on the effects of different hydrodynamic character, sediments diameter distribution and bed forms to the pore water flow in the hyporheic zone. The theory of groundwater- surface water interaction will be illustrated on the analysis of turbulence in the pore water. And then, according to the three-dimensional simulation of surface water and pore water in the hyporheic zone with large eddy simulation model, the character of contaminants transportation between the surface water and pore water will be analyzed and the residence time in the hyporheic zone will be calculated. The effects of different hydrodynamic character, sediments diameter distribution and bed forms to the contaminant transportation and degradation in the hyporheic zone will also be analyzed. At last, we will use the tracer tracking technology to simulate the trajectory of the contaminants in the different surface water and sediments conditions. All of these results will give the technic support to the evaluation of self-purification capacity of hyporheic zone and affection of the pollutant sediments to the surface water.

潜流交换对河流水环境有重要的影响，控制着河道地表水和地下水的物质和能量交换，通过引起溶质在河流系统中的滞留, 影响着溶质在河流中的迁移。本基金拟通过水槽试验以及基于大涡模拟的局部精细紊流模型，分析地表水不同水动力条件、潜流带沉积物颗粒不同特性以及床面不同形貌对潜流带内孔隙水流动的影响规律，从湍流运动特征出发，揭示地表水地下水相互作用原理；根据模拟平台计算得到的潜流带孔隙水间的三维流动，模拟污染物质的输移规律，计算其在潜流带的停留时间，分析沉积物颗粒不同粒径分布、河道不同平面形态对污染物质输移、降解的影响；采用粒子跟踪技术，模拟潜流带中污染物质的吸出规律，分析污染物质在不同地形、不同水流条件下对地表水水环境的影响，为正确评价潜流带对受污染水体的自净能力影响、底泥污染对地表水的影响打下科学基础。

本课题利用多层不同粒径不同排列方式的圆形小球，构建了潜流带局部精细紊流模型，利用大涡模拟技术，模拟了不同水动力条件、不同床面透水率等情况下，潜流带近区水动力特性，湍流运动规律、溶质传输规律等。通过大涡模拟方法，利用双平均理论，分析了理想粗糙透水床面明渠湍流的时空平均特性。统计结果对比前人实验，说明大涡模拟计算结果能够合理地反映流场规律，并由于其对近壁以及床面以下透水区域流场的精细模拟，可在实验室内水槽试验基础上，对明渠湍流时空平均特征理论分析进行很好的补充。提出了在粗糙床面条件下泥水交界面的溶质传质系数计算公式。该公式可利用水深、摩阻流速和床面渗透率来估算溶质交换量，从而定量分析污染物在潜流带和表层水中的交换量，为水污染治理提供技术支撑。同时，建立了水动力—泥沙—磷迁移过程的分相模型。利用修正表面络合模型，模拟不同水化学条件下泥沙颗粒对磷的吸附解吸，克服了分配系数和吸附等温式缺乏普遍性的不足；模型涉及对流扩散、吸附解吸以及水体层和底泥层间的层间交换等物理化学过程，构建了微观过程与宏观规律之间的桥梁，为评估潜流带与水体的物质交换提供了技术支撑。