潜流交换是影响河流-地下水作用带的水流条件、水环境修复、维持生态平衡的重要物理过程之一,河床内存在的黏土透镜体对潜流交换的影响机制尚未得到很好的揭示。参考实际的地质情况,采用适当尺度的物理模型进行黏土透镜体影响下的潜流交换研究。在控制水头和流量的情况下,针对不同规模和埋深的黏土透镜体分别进行潜流交换模拟试验,根据测得的压力数据绘制潜流带内的地下水流场。针对每一种模拟情况,在黏土透镜体上侧、左侧方向的相同距离利用所绘制的等值线计算梯度,得到透镜体附近的流速场,并利用达西定律将流速场转化为流量场。试验结果表明:潜流量随着单一黏土透镜体的尺寸和埋深增加而减小;随着地表水上下游水头差的增大,透镜体迎水面和背水面的流速分别增大和减小且增速逐渐变慢;流速衰减率与地表水上下游水头差呈正相关。研究成果提供了一种研究小尺度的潜流交换过程的方法。
Abstract
Hyporheic exchange is one of the important physical processes that affect the flow conditions of river-groundwater belt, the water environment restoration, and the ecological balance. However, the mechanism of the influence of clay lens on subsurface flow in riverbed has not been well revealed. In this study,the hyporheic exchange under the influence of clay lens is investigated by means of physical modeling with appropriate dimensions with reference to actual geological conditions.Under controlled water head and discharge, the hyporheic exchange is simulated in the presence of varied sizes of clay lens at different depths, and the groundwater flow field in the hyporheic zone is rendered according to the measured pressure data. For each simulation case, the gradient of flow field is calculated using the contours drawn at the same distance from the clay lens in four directions. The velocity field near the lens can then be obtained, and is further transformed to flow field in line with Darcy’s law. The study reveals that hyporheic discharge decreases with the increase of the size and depth of single clay lens.As the water head difference between the upper and lower surface water increases, the flow velocity increases at the upstream face of clay lens with an attenuating growth rate, but reduces at the back side of the lens with an aggravating reduction rate. In addition, a method for studying small scale subsurface flow exchange processes is also provided.
关键词
黏土透镜体 /
物理模型 /
潜流交换 /
达西定律 /
流速衰减率
Key words
clay lens /
physical model /
hyporheic exchange /
Darcy’s law /
velocity of flow
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基金
流域水文循环模拟与调控国家重点实验室开放研究基金项目(IWHR-SKL-201502);
河海大学中央高校基本科研业务费项目(2015B14414);
江苏省大学生创新创业训练计划项目(201610294004Y)
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