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Abstract

The main goal of this study is to deepen the understanding of coupled processes in the subsurface of Berlin, capital city of Germany. The study area is located in the North-east German Basin, which displays a sedimentary infill of several kilometers. These sediments are composed of a sequence of alternating aquifers and aquitards, which include the local Oligocene Rupelian aquitard. This unit is characterized by a comparatively low hydraulic conductivity, thus separating the overlying fresh water aquifers, from whom Berlin produces 100% of its drinking water, from the underlying saline aquifers. In this context, newly available hydraulic data were integrated into 3D thermohydraulic models of the sub-surface, specifically investigating the coupling of surface water bodies to the subsurface. These models also serve as a basis for future thermohaline simulations as there is evidence of highly mineralized waters in the subsurface which indicates the vulnerability of shallow groundwater utilization beneath the city. The resulting thermal and hydraulic configuration shows, that the coupling of surface water bodies and groundwater might lead to significant modifications of predicted subsurface temperatures and fluid velocities. These modifications are most drastic in areas where the hydraulic head of surface water bodies is highly different compared to the sur-rounding aquifer. Consequently, differences in the predicted groundwater flow field also result in differences in predicted temperatures because of advective heat transport. In this context, the presence of major lakes might account for temperature differences up to 5°C and major rivers in the model area lead to temperature differences on the order of 1°C.