Abstract
Abstract. This study presents the development of tools for the sustainable thermal management of a shallow unconsolidated urban groundwater body in the city of Basel (Switzerland). The concept of the investigations is based on (1) a characterization of the present thermal state of the urban groundwater body, and (2) the evaluation of potential mitigation measures for the future thermal management of specific regions within the groundwater body. The investigations focus on thermal processes down-gradient of thermal groundwater use, effects of heated buildings in the subsurface as well as the thermal influence of river–groundwater interaction. Investigation methods include (1) short- and long-term data analysis, (2) high-resolution multilevel groundwater temperature monitoring, as well as (3) 3-D numerical groundwater flow and heat transport modeling and scenario development. The combination of these methods allows for the quantifying of the thermal influences on the investigated urban groundwater body, including the influences of thermal groundwater use and heated subsurface constructions. Subsequently, first implications for management strategies are discussed, including minimizing further groundwater temperature increase, targeting "potential natural" groundwater temperatures for specific aquifer regions and exploiting the thermal potential.
Highlights
Thermal groundwater regimes in urban areas are affected by numerous anthropogenic changes, such as surface sealing or subsurface constructions as well as groundwater use
The analyses show how to predict the influence of thermal systems and urban subsurface development on the basis of field-scale hydrogeological data as well as 3-D numerical groundwater flow and heat transport modeling and scenario development
The variation in measured temperature data is the combined result of (1) heat transport from the ground surface by conduction as well as by convection with water infiltrating through the unsaturated zone and into the saturated porous medium, (2) river–groundwater interaction, as well as (3) thermal influence of thermal groundwater users and urbanization
Summary
Thermal groundwater regimes in urban areas are affected by numerous anthropogenic changes, such as surface sealing or subsurface constructions as well as groundwater use. In northwestern Switzerland, Basel, groundwater temperatures have increased significantly, and have reached up to 17 ◦C in an area where the long-term average annual air temperature is approximately 10 ◦C (Epting et al, 2011). This increase is substantial, considering the groundwater temperatures in areas not influenced by anthropogenic activities should be comparable to the average annual air temperature. Understanding groundwater heat transport is essential for the design, performance analysis and impact assessment of thermal devices (e.g. Fujii et al, 2005)
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