Center for Applied Geoscience (ZAG), University of Tübingen, Sigwartstraße 10, 72076 Tübingen, Germany.
Ground Water. 2011 Jul-Aug;49(4):491-502. doi: 10.1111/j.1745-6584.2010.00745.x. Epub 2010 Oct 6.
Infiltrating river water carries the temperature signal of the river into the adjacent aquifer. While the diurnal temperature fluctuations are strongly dampened, the seasonal fluctuations are much less attenuated and can be followed into the aquifer over longer distances. In one-dimensional model with uniform properties, this signal is propagated with a retarded velocity, and its amplitude decreases exponentially with distance. Therefore, time shifts in seasonal temperature signals between rivers and groundwater observation points may be used to estimate infiltration rates and near-river groundwater velocities. As demonstrated in this study, however, the interpretation is nonunique under realistic conditions. We analyze a synthetic test case of a two-dimensional cross section perpendicular to a losing stream, accounting for multi-dimensional flow due to a partially penetrating channel, convective-conductive heat transport within the aquifer, and heat exchange with the underlying aquitard and the land surface. We compare different conceptual simplifications of the domain in order to elaborate on the importance of different system elements. We find that temperature propagation within the shallow aquifer can be highly influenced by conduction through the unsaturated zone and into the underlying aquitard. In contrast, regional groundwater recharge has no major effect on the simulated results. In our setup, multi-dimensionality of the flow field is important only close to the river. We conclude that over-simplistic analytical models can introduce substantial errors if vertical heat exchange at the aquifer boundaries is not accounted for. This has to be considered when using seasonal temperature fluctuations as a natural tracer for bank infiltration.
渗入河水中的水流将河水的温度信号带入相邻的含水层。尽管昼夜温度波动被强烈衰减，但季节波动的衰减程度要小得多，并且可以在更长的距离内被跟踪到含水层中。在具有均匀性质的一维模型中，该信号以延迟速度传播，其幅度随距离的增加呈指数衰减。因此，河流和地下水观测点之间季节温度信号的时间滞后可用于估计入渗率和近河地下水速度。然而，正如本研究所示，在实际条件下，这种解释并不是唯一的。我们分析了一个垂直于损耗流的二维横截面的合成测试案例，考虑了由于部分穿透渠道而导致的多维流动、含水层内的对流-传导热传输以及与下面的隔水层和地表的热交换。我们比较了不同的域概念简化，以阐述不同系统元素的重要性。我们发现，浅层含水层内的温度传播可以受到不饱和带和下面的隔水层的传导的高度影响。相比之下，区域地下水补给对模拟结果没有重大影响。在我们的设置中，流场的多维性仅在靠近河流的地方很重要。我们得出的结论是，如果不考虑含水层边界的垂直热交换，过于简化的分析模型可能会引入大量误差。在将季节温度波动用作河岸入渗的天然示踪剂时，必须考虑到这一点。
