Abstract This study evaluates the utility of ambient temperature profiles collected in sealed bedrock boreholes to assess variability in groundwater flow in discretely fractured shallow bedrock environments. A conceptual model for groundwater flow and groundwater-surface water temperature conditions and their interaction in a temperate climate is developed through a statistical interpretation of time-lapse thermal deviation logs. Temperature profiles were collected in three angled and three vertical boreholes drilled to 24–32 mbgs (meters below ground surface) and temporarily sealed with an impermeable fabric liner in a fractured dolostone bedrock aquifer adjacent to and extending beneath a bedrock river to monitor seasonal hydrodynamics. Ambient borehole temperature profiles collected every 1–8 weeks over a 12 month period identified zones of hydraulic activity during periods of intra-seasonal stability without the interference of open borehole cross-connection. Signal cross-correlation and Fourier spectra analysis of thermal deviation logs provided a novel way to observe the shallow bedrock flow system’s temperature evolution due to advection along discrete fractures in response to seasonal transience, and to identify and isolate noise caused by free-convection cells within the sealed borehole. This approach represents a diagnostic tool that improves confidence in identifying depth discrete, hydraulically active fracture zones from thermal deviation data sets in a shallow, fractured sedimentary bedrock environment. Variably scaled free-convection cells were observed within the borehole water columns during the colder winter periods. Although these periods were accompanied by higher signal noise near the river/atmospheric interface, these cells led to a temporary thermal disequilibrium between the borehole water column and formation water deeper in the bedrock. These conditions increased the maximum depth of thermal detections associated with discrete groundwater flow features from 14 mbgs in the summer to 26 mbgs in the winter, thereby enhancing the understanding of shallow groundwater flow systems under the direct influence of surface water.

中文翻译：

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密封基岩钻孔中季节性动态环境温度剖面的水文解释

摘要 本研究评估了在密封基岩钻孔中收集的环境温度剖面的效用，以评估离散裂缝浅层基岩环境中地下水流的可变性。通过对延时热偏差测井的统计解释，开发了地下水流和地下水-地表水温度条件及其在温带气候中的相互作用的概念模型。温度分布在三个倾斜的和三个垂直钻孔中收集，钻孔深度为 24-32 mbgs（地表以下米），并在靠近基岩河并在基岩河下方延伸的断裂白云岩基岩含水层中用不透水织物衬垫临时密封，以监测季节性流体动力学。在 12 个月的时间段内每 1-8 周收集一次环境钻孔温度剖面，确定了季节性稳定时期内的水力活动区域，而不受开放钻孔交叉连接的干扰。热偏差测井的信号互相关和傅立叶谱分析提供了一种新的方法来观察浅层基岩流动系统由于响应季节性瞬变而沿着离散裂缝的平流而引起的温度演变，以及识别和隔离由内部自由对流单元引起的噪声。密封的钻孔。这种方法代表了一种诊断工具，可以提高从浅层断裂沉积基岩环境中的热偏差数据集中识别深度离散、水力活动断裂带的信心。在较冷的冬季期间，在钻孔水柱内观察到不同比例的自由对流单元。尽管这些时期伴随着河流/大气界面附近较高的信号噪声，但这些细胞导致钻孔水柱和基岩深处地层水之间的暂时热不平衡。这些条件将与离散地下水流特征相关的热探测的最大深度从夏季的 14 mbgs 增加到冬季的 26 mbgs，从而增强了对地表水直接影响下浅层地下水流系统的理解。这些细胞导致钻孔水柱和基岩深处的地层水之间出现暂时的热不平衡。这些条件将与离散地下水流特征相关的热探测的最大深度从夏季的 14 mbgs 增加到冬季的 26 mbgs，从而增强了对地表水直接影响下浅层地下水流系统的理解。这些细胞导致钻孔水柱和基岩深处的地层水之间出现暂时的热不平衡。这些条件将与离散地下水流特征相关的热探测的最大深度从夏季的 14 mbgs 增加到冬季的 26 mbgs，从而增强了对地表水直接影响下浅层地下水流系统的理解。