Abstract

In the unlined Tuxbach water transfer tunnel, running between Hintertux (1,500 m asl) and the Schlegeis Reservoir (Austria), a local geothermal anomaly with temperatures up to 14.6 °C exists. These temperatures are around 3 °C higher than expected, considering the tunnel’s shallow depth, together with its surrounding alpine environment and regional heat flow. This is especially noticeable because the temperatures have remained stable since the tunnel’s construction in 1969, although the tunnel is generally cooling the surrounding rock massive. The objective of this investigation is to explain the origin of the anomaly with hydrogeological methods and to evaluate the hydrogeological properties of the gneisses exposed in the tunnel. The anomaly is caused by the high hydraulic conductivity (~2.5∙10⁻⁵ m s⁻¹) within a narrow shear-zone core, part of the Tux Shear Zones in the Ahorn Gneiss Core. The zone triggers fast groundwater transport over 1.5 km from both sides towards the tunnel. One reason is that the morphology provides thicker overburden with growing distance from the tunnel and therefore higher temperatures on the same horizontal level in the directions of the fault plane. The second explanation is that the narrowness of the shear zone permits effective heat transfer similar to a heat exchanger. No hydrothermal water share is recognizable; instead, mainly cold glacial melt water and snow contribute to the section of the anomaly and all other runouts of the tunnel. Factually based results show the disproportionately high contribution of snow and glaciers to the groundwater recharge in this alpine hard-rock aquifer.

中文翻译：

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冰川融化的水补充了Ahorn片麻岩的持续局部热异常（奥地利）

摘要

在Hintertux（1,500 m asl）和Schlegeis Reservoir（奥地利）之间运行的无衬砌Tuxbach输水隧道中，存在温度高达14.6°C的局部地热异常。考虑到隧道的浅深度，周围的高山环境和区域热流，这些温度比预期的温度高约3°C。这一点特别值得注意，因为自1969年隧道建成以来，温度一直保持稳定，尽管隧道通常正在冷却周围的大量岩石。这项研究的目的是用水文地质方法解释异常的起源，并评估暴露在隧道中的片麻岩的水文地质特性。异常是由于较高的水力传导率（〜2.5∙10 ^-5  m s^-1）在狭窄的剪切带岩心中，是Ahorn片麻岩岩心的Tux剪切带的一部分。该区域触发了从两侧到隧道超过1.5公里的快速地下水运输。原因之一是，随着距隧道距离的增加，该形态提供了更厚的覆盖层，因此在断层平面方向上的同一水平面上的温度更高。第二种解释是，剪切区的狭窄程度允许类似于热交换器的有效传热。没有可识别的热热水份额；取而代之的是，主要是冰河融化的水和雪造成了断层的异常以及隧道的所有其他跳动。基于事实的结果表明，在该高山硬岩含水层中，雪和冰川对地下水补给的贡献不成比例。