Investigating patterns and controls of groundwater up-welling in a lowland river by combining Fibre-optic Distributed Temperature Sensing with observations of vertical hydraulic gradients
Investigating patterns and controls of groundwater up-welling in a lowland river by combining Fibre-optic Distributed Temperature Sensing with observations of vertical hydraulic gradients
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DOI：
10.5194/hess-16-1775-2012
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发表时间：
2012-06
影响因子：
6.3
通讯作者：
S. Krause;T. Blume;N. Cassidy
中科院分区：
文献类型：
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作者：
S. Krause;T. Blume;N. Cassidy
本文利用光纤分布式温度传感器(FO-DTS)识别的河床温度异常和垂直水力梯度(VHG)观测相结合的方法，研究了急流低洼河流含水层-河流交换的模式和控制。沿着这条低地河段的FO-DTS温度轨迹显示出离散的模式，“冷点”表明地下水正向上涌出。与以前使用FO-DTS调查地下水-地表水交换的研究不同，本研究中的光纤电缆埋在河床沉积物中，即使水流很快，流量也很大，也能确保信号清晰。在观测的夏季基流期间，发现地下水上升处的河床温度比环境河床温度低1.5℃。由于河流流量大，冷点尖锐且局部化明显，对下游地表水温没有明显影响。沿河流段的VHG模式在空间上变化很大，即使在小尺度上也显示出强烈的差异。VHG模式本身既是河床结构非均质性的指标，也是地下水-地表水交换通量空间非均质性的指标，因此对它们的解释并不是决定性的。然而，结合高空间分辨率的FO-DTS数据，我们能够将这两种影响分开，并清楚地确定增强交换的位置，同时还获得了导致非常离散的交换模式的复杂的小尺度河床透过率模式的信息。VHG和FO-DTS组合方法的验证为分析地下水-地表水交换的驱动因素和控制因素提供了一种有效的战略，并对含水层-河流界面的生物地球化学循环和污染物迁移的量化产生了影响。
This paper investigates the patterns and controls of aquifer–river exchange in a fast-flowing lowland river by the conjunctive use of streambed temperature anomalies identified with Fibre-optic Distributed Temperature Sensing (FO-DTS) and observations of vertical hydraulic gradients (VHG). FO-DTS temperature traces along this lowland river reach reveal discrete patterns with "cold spots" indicating groundwater up-welling. In contrast to previous studies using FO-DTS for investigation of groundwater–surface water exchange, the fibre-optic cable in this study was buried in the streambed sediments, ensuring clear signals despite fast flow and high discharges. During the observed summer baseflow period, streambed temperatures in groundwater up-welling locations were found to be up to 1.5 °C lower than ambient streambed temperatures. Due to the high river flows, the cold spots were sharp and distinctly localized without measurable impact on down-stream surface water temperature. VHG patterns along the stream reach were highly variable in space, revealing strong differences even at small scales. VHG patterns alone are indicators of both, structural heterogeneity of the stream bed as well as of the spatial heterogeneity of the groundwater–surface water exchange fluxes and are thus not conclusive in their interpretation. However, in combination with the high spatial resolution FO-DTS data we were able to separate these two influences and clearly identify locations of enhanced exchange, while also obtaining information on the complex small-scale streambed transmissivity patterns responsible for the very discrete exchange patterns. The validation of the combined VHG and FO-DTS approach provides an effective strategy for analysing drivers and controls of groundwater–surface water exchange, with implications for the quantification of biogeochemical cycling and contaminant transport at aquifer–river interfaces.