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One solution for reducing the current consumption of fossil fuels is a more frequent use of shallow geothermal energy. However, particularly regarding urban subsurface resources, increased use conflicts are predictable. Consequently, reasonable exploitation of subsurface resources requires an assessment of technologically achievable energy potentials with scientific based tools. We present application-oriented management tools which target on deriving shallow subsurface energy potentials. 3D groundwater flow and heat-transport models are used to capture groundwater flow and heat-transport dynamics on the city- and quarter-scale, 2D box models are used to quantify technically feasible extraction rates of well doublets for groundwater heat pump systems. For Basel (Switzerland), prospective large theoretical energy potentials can be derived for areas with high advective heat flux and high temperature gradients. Likewise, single city quarters are suitable for ‘active’ thermal use with well doublets, whereas thermal power potentials reach 1.2 MW. Regarding ‘passive’ installations of energy absorbers in subsurface structures located within the groundwater, energy potentials amount to 4 and up to 40 W m−2. The assessment results can be integrated into urban energy plans and support architects, city planners and potential users to acquire initial site-specific information on the technical feasibility of shallow geothermal energy systems.

Topographically induced Alpine regional groundwater flow systems below the unconsolidated valley fillings constitute a substantial unused geothermal resource. Within the framework of the INTERREG VB project GRETA (shallow geothermal energy in the Alpine region), we developed a method to quantify the groundwater flux of complex alpine aquifers. The basis of the study is a regional-scale hydraulic groundwater model, which is based on a 3D tectonic model of the Davos region in Switzerland. Based on data from a large pumping test, we were able to calibrate the hydraulic model and to calculate basics for various usage scenarios of energetic exploitation for the Arosa Dolomite aquifer. Favourable conditions for an energetic exploitation are related to large-scale topography differences between groundwater recharge and potential exfiltration areas in the valleys, thanks to the 3D geometry of the large-area tectonic nappe units with their root zone located within river valleys. In general, the proposed concept could be applied to manifold similar geological and hydrogeological settings of the Alpine belt.

In regional scale aquifers in the Rhine Valley and Tabular Jura east of Basel (Switzerland), the groundwater circulation was investigated using regional-scale geological and hydraulic 3D models. The main aquifers in the area comprise the Quaternary aquifer of unconsolidated gravel deposits along the River Rhine and its tributaries, as well as the regional scale karst aquifer within the Upper Muschelkalk. Land subsidence, a process likely associated with salt solution mining, indicates further subordinate groundwater bearing segments and complex groundwater interactions along fault zones. In the aquifer systems we investigated, regional-scale groundwater circulation was simulated and visualized in relation to the geological settings. Lithostratigraphic units and fault structures were parameterized and analyzed, including the sensitivity of hydraulic properties and boundaries. Scenario calculations were used to investigate the sensitivity that the aquifer systems had to hydraulic parameter changes during Quaternary aggradation and degradation in the main valley. Those calculations were also done for base-level changes in the Rivers Rhine and Birs. For this purpose, this study considered probable historic base-levels before river regulation occurred, and before river dams and power plants were constructed. We also focused on scenarios considering increased groundwater recharge rates, e.g. due to exceptional long-lasting precipitation, or heavy rainfall events in the catchment area. Our results indicate that increased groundwater recharge rates in the catchment areas during such events (or periods) are associated with orders of magnitude increases of regional inflow into the Upper Muschelkalk karst aquifer. Furthermore, the groundwater fluctuations and groundwater saturated regions within the karst aquifer shift to places where high densities of sinkholes are documented. When the surface water base-levels adapt to probable historic levels, it leads to increased hydraulic gradients (i.e. local lowering of the groundwater level by up to 7 m). Those increased gradients are associated with increased groundwater flow within some aquifer regions that are particularly prone to karst development.

A three-dimensional groundwater model was used to improve water resource management for a study area in north-west Switzerland, where drinking-water production is close to former landfills and industrial areas. To avoid drinking-water contamination, artificial groundwater recharge with surface water is used to create a hydraulic barrier between the contaminated sites and drinking-water extraction wells. The model was used for simulating existing and proposed water management strategies as a tool to ensure the utmost security for drinking water. A systematic evaluation of the flow direction between existing observation points using a developed three-point estimation method for a large number of scenarios was carried out. It is demonstrated that systematically applying the developed methodology helps to identify vulnerable locations which are sensitive to changing boundary conditions such as those arising from changes to artificial groundwater recharge rates. At these locations, additional investigations and protection are required. The presented integrated approach, using the groundwater flow direction between observation points, can be easily transferred to a variety of hydrological settings to systematically evaluate groundwater modelling scenarios.

Geotechnical problems during and after tunnel construction are often related to groundwater circulation. In tunnelling projects, however, groundwater flow systems are often only partly known. This uncertainty is manifested by the typically scarce hydraulic data that limits the understanding of subsurface hydrogeological processes. In particular, there is a general lack of data documenting groundwater flow changes caused by tunnelling. The present paper presents a concept involving an iterative understanding of subsurface hydrogeological systems influenced by tunnelling. A major challenge of our approach consists of integrating complex geological geometries from a 3D geological model (GOCAD) into a numerical groundwater flow model (COMSOL Multiphysics). The starting point is a 3D geological model representing a regional tectonic system located in the Jura Mountains in Switzerland. This geological model is transferred into regional and local-scale groundwater flow models. Due to the lack of hydrogeological data, a 3D view of geological–hydrogeological systems is often required to respond to groundwater-induced geotechnical problems in tunnelling. Numerical groundwater flow models make it possible to perform sensitivity analysis and to test how boundary conditions and hydraulic property distributions influence calculated groundwater flow regimes. In addition, our approach enables testing the effects of changes of hydraulic regimes due to tunnel excavation at different scales.

The shallow subsurface in urban areas is increasingly used by shallow geothermal energy systems as a renewable energy resource and as a cheap cooling medium, e.g. for building air conditioning. In combination with further anthropogenic activities, this results in altered thermal regimes in the subsurface and the so-called subsurface urban heat island effect. Successful thermal management of urban groundwater resources requires understanding the relative contributions of the different thermal parameters and boundary conditions that result in the “present thermal state” of individual urban groundwater bodies. To evaluate the “present thermal state” of urban groundwater bodies, good quality data are required to characterize the hydraulic and thermal aquifer parameters. This process also involved adequate monitoring systems which provide consistent subsurface temperature measurements and are the basis for parameterizing numerical heat-transport models. This study is based on previous work already published for two urban groundwater bodies in Basel (CH) and Zaragoza (ES), where comprehensive monitoring networks (hydraulics and temperature) as well as calibrated high-resolution numerical flow- and heat-transport models have been analyzed. The “present thermal state” and how it developed according to the different hydraulic and thermal boundary conditions is compared to a “potential natural state” in order to assess the anthropogenic thermal changes that have already occurred in the urban groundwater bodies we investigated. This comparison allows us to describe the various processes concerning groundwater flow and thermal regimes for the different urban settings. Furthermore, the results facilitate defining goals for specific aquifer regions, including future aquifer use and urbanization, as well as evaluating the thermal use potential for these regions. As one example for a more sustainable thermal use of subsurface water resources, we introduce the thermal management concept of the “relaxation factor”, which is a first approach to overcome the present policy of “first come, first served”. Remediation measures to regenerate overheated urban aquifers are also introduced. The transferability of the applied methods to other urban areas is discussed. It is shown that an appropriate selection of locations for monitoring hydraulic and thermal boundary conditions make it possible to implement representative interpretations of groundwater flow and thermal regimes as well as to set up high-resolution numerical flow- and heat-transport models. Those models are the basis for the sustainable management of thermal resources.

Swelling of clay-sulfate rocks is a feared problem in tunneling in such rock, causing heave of the tunnel invert and leading to swelling pressures that seriously damage the tunnel lining. Prediction of the swelling potential of rocks in different tunnel sections and tools to evaluate measures that aim at reducing the swelling risk would be a major aid for designers of tunneling projects and rehabilitation works in order to respond adequately to the swelling problem. The study presents a hydrogeological approach to assess the swelling potential of clay-sulfate rocks in tunneling, using the Belchen tunnel in Switzerland as a case study. It shows that this approach can be applied to complex geological settings using structurally consistent 3D numerical models to simulate groundwater flow influenced by tunneling. The models are in particular used to evaluate hydraulic measures that aim at preventing or minimizing water inflow into clay-sulfate rocks after tunneling. Analyzed hydraulic measures include pumping shafts connected to the tunnel drainage, sealing structures applied to the rock zone around the tunnel damaged by the excavation process (excavation damaged zone), as well as groundwater level drawdown in aquifers crossing the tunnel. A sensitivity study addresses model uncertainties and evaluates the impact of model parameters on the swelling potential. Promising measures include the installation of pumping shafts in tunnel sections of clay-sulfate rocks at the border to aquifers and permeable fault zones. The study shows that monitoring of hydraulic heads as well as of groundwater volumes drained by the tunnel would increase the predictive capability of the models. Presented results are site specific. However, the approach to assess the swelling potential of clay-sulfate rocks in tunneling, and to assess hydraulic measures to respond to the swelling problem, can be transferred to other tunneling projects.

Tracer testing is a well-established technique in hydrogeological site characterization. However, certain a priori knowledge of the hydraulic regime is required beforehand to avoid test failure, e.g. miss of tracer. In this study, we propose a novel tracer test concept for the hydraulic characterization of shallow unconsolidated sedimentary deposits when only scarce a priori information on the hydraulic regime is available. Therefore, we combine conventional salt tracer testing with direct push vertical high resolution electrical conductivity logging. The proposed tracer test concept was successfully tested on coarse, braided river deposits of the Tagliamento River, Italy. With limited a priori information available two tracer tests were performed in three days to reliably determine ground water flow direction and velocity allowing on-site decision-making to adaptively install observation wells for reliable breakthrough curve measurements. Furthermore, direct push vertical electrical profiling provided essential information about the plume characteristics with outstanding measurement resolution and efficiency.

Shallow geothermal resource exploitation through the use of groundwater heat pump systems not only has hydraulic and thermal effects on the environment but also induces physicochemical changes that can compromise the operability of installations. This study focuses on chemical clogging and dissolution subsidence processes observed during the geothermal re-injection of pumped groundwater into an urban aquifer. To explain these phenomena, two transient reactive transport models of a groundwater heat pump installation in an alluvial aquifer were used to reproduce groundwater-solid matrix interactions occurring in a surrounding aquifer environment during system operation. The models couple groundwater flow, heat and solute transport together with chemical reactions. In these models, the permeability distribution in space changes with precipitation-dissolution reactions over time. The simulations allowed us to estimate the calcite precipitation rates and porosity variations over space and time as a function of existent hydraulic gradients in an aquifer as well as the intensity of CO2 exchanges with the atmosphere. The results obtained from the numerical model show how CO2 exolution processes that occur during groundwater reinjection into an aquifer and calcite precipitation are related to hydraulic efficiency losses in exploitation systems. Finally, the performance of reinjection wells was evaluated over time according to different scenarios until the systems were fully obstructed. Our simulations also show a reduction in hydraulic conductivity that forces re-injected water to flow downwards, thereby enhancing the dissolution of evaporitic bedrock and producing subsidence that can ultimately result in a dramatic collapse of the injection well infrastructure.

Riverbank filtration (RBF) is used worldwide to produce high quality drinking water. With river water often contaminated by micropollutants (MPs) from various sources, this study addresses the occurrence and fate of such MPs at three different RBF sites with oxic alluvial sediments and short travel times to the drinking water well down to hours. A broad range of MPs with various physico-chemical properties were analysed with detection limits in the low ng L−1 range using solid phase extraction followed by liquid chromatography coupled to tandem high resolution mass spectrometry. Out of the 526 MPs targeted, a total of 123 different MPs were detected above the limit of quantification at the three different RBF sites. Of the 75–96 MPs detected in each river, 43–59% were attenuated during RBF. The remaining total concentrations of the MPs in the raw drinking water accounted to 0.6–1.6 μgL−1 with only a few compounds exceeding 0.1 μgL−1, an often used threshold value. The attenuation was most pronounced in the first meters of infiltration with a full elimination of 17 compounds at all three sites. However, a mixing with groundwater related to regional groundwater flow complicated the characterisation of natural attenuation potentials along the transects. Additional non-target screening at one site revealed similar trends for further non-target components. Overall, a risk assessment of the target and estimated non-target compound concentrations finally indicated during the sampling period no health risk of the drinking water according to current guidelines. Our results demonstrate that monitoring of contamination sources within a catchment and the affected water quality remains important in such vulnerable systems with partially short residence times., Graphical abstract Image 1, Highlights • 123 of 500 micropollutants were detected with LC-ESI-HRMS/MS in surface and groundwater samples. • About 50% of the micropollutants were attenuated during riverbank filtration with short residence times. • 17 micropollutants were attenuated >50% at all 3 sites within 50%. • Target and non-target screening of raw water indicate no significant human health risk.

Infrastructures that are constructed on unstable geologic formations are prone to subsidence. Data have been collected in the context of an upgrading project for a highway located beside a river dam that was constructed on gypsum-containing formations. Surface water infiltrates upstream of the dam, circulates through the gravel deposits and into the weathered bedrock around and beneath the dam, and exfiltrates downstream into the river. As a result, an extended weathering zone within the bedrock and preferential flow paths within voids and conduits developed as part of a rapidly evolving karst system. These processes enhance karstification in the soluble units of the gypsum-containing formations and resulted in the subsidence of the dam and the highway. Since 2006 changes in the hydrogeologic flow regime have been investigated continuously by different methods that also allow the evaluation of the long-term performance of the infrastructures. Geological (outcrops, lithostratigraphic information of boreholes), hydrometrical (extensive groundwater monitoring, dye tracer tests) and hydrogeophysical (Electrical Resistivity Tomography, ERT) field data of varying quality were integrated into high-resolution 3-D hydrogeological and 2-D karst evolution models. The applied investigative methods are validated and the sensitivity of relevant parameters governing the processes determined. It could be demonstrated that the applied methods for karst aquifer characterization complement each other and allow the interpretation of short-term impacts and long-term development on system-dynamics in the context of hydrogeologic flow regimes of karst areas. This includes the description of the transient character of the hydrogeologic flow regime during and after episodic flood events (surface-groundwater interaction, conduit and diffuse model outflow) as well as the evaluation of time scales for karst evolution. Results allow the optimization of investigative methods for similar subsidence problems, leading from general measurements and monitoring technologies to tools with predictive character.

In the northwestern area of Basel, Switzerland, a tunnel highway connects the French highway A35 (Mulhouse–Basel) with the Swiss A2 (Basel–Gotthard–Milano). The subsurface highway construction was associated with significant impacts on the urban groundwater system. Parts of this area were formerly contaminated by industrial wastes, and groundwater resources are extensively used by industry. During some construction phases, considerable groundwater drawdown was necessary, leading to major changes in the groundwater flow regime. Sufficient groundwater supply for industrial users and possible groundwater pollution due to interactions with contaminated areas had to be taken into account. A groundwater management system is presented, comprising extensive groundwater monitoring, high-resolution numerical groundwater modeling, and the development and evaluation of different scenarios. This integrated approach facilitated the evaluation of the sum of impacts, and their interaction in time and space with changing hydrological boundary conditions. For all project phases, changes of the groundwater system had to be evaluated in terms of the various goals and requirements. Although the results of this study are case-specific, the overall conceptual approach and methodologies applied may be directly transferred to other urban areas.

Increasing anthropogenic impacts lead to elevated temperatures of the shallow subsurface, including the unsaturated and groundwater saturated zone, in many urban areas in comparison to unaffected natural thermal states. The "current thermal state" of four groundwater bodies in the urban area of Basel-City, Switzerland, was investigated by means of high-resolution multilevel temperature wells and numerical 3D groundwater flow and heat transport models. The calibrated and validated numerical groundwater flow and heat transport models allow evaluating and comparing groundwater and heat fluxes for the investigated groundwater bodies and defined cross-sections for differing urban districts, e.g. residential and industrial areas under development. We present the overall and the specific advective heat fluxes within two urban districts, which will be restructured in the near future. The management of groundwater resources in urban areas plays an important role not only for groundwater quantity but also for its quality, i.e. thermal subsurface and groundwater regimes. We demonstrate how monitoring and modelling tools can be the basis for a sustainable management of complex urban groundwater resources. Furthermore, we argue that such tools should be integrated in the thermal management of urban groundwater bodies. Such tools also allow integrating the potentially available energy of shallow subsurface resources into energetic management strategies on the urban scale.

The presented work illustrates to what extent field investigations as well as monitoring and modeling approaches are necessary to understand the high discharge dynamics and vulnerability of Karst springs. In complex settings the application of 3D geological models is essential for evaluating the vulnerability of Karst systems. They allow deriving information on catchment characteristics, as the geometry of aquifers and aquitards as well as their displacements along faults. A series of Karst springs in northwestern Switzerland were compared and Karst system dynamics with respect to qualitative and quantitative issues were evaluated. The main objective of the studies was to combine information of catchment characteristics and data from novel monitoring systems (physicochemical and microbiological parameters) to assess the intrinsic vulnerability of Karst springs to microbiological contamination with simulated spring discharges derived from numerical modeling (linear storage models). The numerically derived relation of fast and slow groundwater flow components enabled us to relate different sources of groundwater recharge and to characterize the dynamics of the Karst springs. Our study illustrates that comparably simple model-setups were able to reproduce the overall dynamic intrinsic vulnerability of several Karst systems and that one of the most important processes involved was the temporal variation of groundwater recharge (precipitation, evapotranspiration and snow melt). Furthermore, we make a first attempt on how to link intrinsic to specific vulnerability of Karst springs, which involves activities within the catchment area as human impacts from agriculture and settlements. Likewise, by a more detailed representation of system dynamics the influence of surface water, which is impacted by release events from storm sewers, infiltrating into the Karst system, could be considered. Overall, we demonstrate that our approach can be the basis for a more flexible and differentiated management and monitoring of raw-water quality of Karst springs.

Drinking water production in the vicinity of rivers not only requires the consideration of different spatiotemporal scales and settings of river-groundwater interaction processes, but also of local and regional scale groundwater regimes. Selected case studies in combination with field-experiments and the setup of high-resolution groundwater flow models enabled the investigation of the spatiotemporal development of microbial (classical fecal indicator bacteria and total cell counts) and selected organic micropollutants in riverine and regional groundwater for different hydrological settings, including low and high flow conditions. Proxy indicators suitable as surrogates for the diverse contaminations in alluvial aquifers with different settings could be identified. Based on the study results, the basic elements for both groundwater management and river restoration concepts are derived, which include the: (1) compilation and evaluation of the "current state" concerning hydrogeology, microbiology and contamination by organic micropollutants, (2) definition of field-experiments to qualitatively assess variability related to the "current state", and (3) quantitative assessment of groundwater regimes, including variability of groundwater components and inflow areas, by application of high-resolution groundwater flow models. The validity and transferability of the concept and inferred controls (specifically drivers and controls of river-groundwater interaction) are tested by evaluations derived from hydraulic relationships to river sections with comparable settings and regional groundwater flow regimes in general. The results of our investigations illustrate the influence of dynamic hydrologic boundary conditions on river-groundwater interaction and of regional scale groundwater flow regimes on the water composition of riverine groundwater systems. It is demonstrated how to identify river sections and their variations with intensified river-groundwater exchange processes and how to quantify the transient character of the different groundwater components that constitute the raw water quality of drinking water wells near rivers.

This work presents preliminary evaluation elements for geothermal potential assessment and thermal influences of planned tunnel infrastructures for the urban agglomeration of Basel (Switzerland). In dependence of the tunnel type (motorway or railway) as well as its location related to the geological and hydrogeological settings different solutions for shallow geothermal energy systems (SGE) are investigated. ‘Passive’ and ‘active’ SGE have been evaluated, including heat-exchanging segments installed in tunnel lining structures and thermal exploitation of water circulating in culvert systems. First results suggest that thermal activation of a planned railway tunnel is most efficient where it is located within groundwater-saturated zones of the unconsolidated rock deposits. In summer, thermal power of 3.7 and 1.4 MW can be exchanged from two 736 and 284 m-long tunnel sections, respectively. Accordingly, in standard heat pump operating conditions a thermal energy of 10.4 and 3.8 GWh can be delivered for ‘cooling’. In winter, thermal power of 1.9 and 0.7 MW can be exchanged, respectively, and a thermal energy of 5.2 and 1.9 GWh can be delivered for ‘heating’. SGE within culverts reveals to be favorable in heating mode only and for sections where the motorway tunnel runs perpendicular to the regional groundwater flow field and where ambient groundwater temperatures are high. Under such conditions along a 320 m-long tunnel section thermal power of up to 0.4 MW can be provided in summer and 0.8 MW in winter, respectively, and thermal energy of 1.1 GWh in summer and 2.1 GWh in winter, can be delivered.

Summary A superposition of several thermal processes leads to an elevation of groundwater temperatures of up to 9 °C above the natural state in the city of Basel, Switzerland. The urban thermal groundwater regime is influenced by: (1) urbanization and annual heating periods; (2) thermal groundwater use; (3) seasonal trends; (4) river-groundwater interaction; and (5) climate change and consequences thereof. The combination of short- and long-term data analysis, including conventional and high-resolution multilevel groundwater temperature monitoring, as well as 3D numerical groundwater flow and heat-transport modeling allowed quantifying the thermal influences on the investigated urban groundwater body. Results facilitate to describe the “present state” of the urban thermal groundwater regime and to derive a “potential natural state” of the investigated groundwater body. The study originated from a request of the executive council to provide a basis for cost estimates of infrastructure adaptation measures necessary to mitigate the impact of climate change. It is shown that the principal trigger for the observed thermal development is not climate change but that local and regional anthropogenic factors are dominating. Although in urban areas, groundwater is increasingly used for cooling purposes; the geothermal potential, resulting from elevated groundwater temperatures, is generally not exploited. The presented approach provides a basis for the setup of combined and thermally balanced heating and cooling systems.

Shallow subsurface thermal regimes in urban areas are increasingly impacted by anthropogenic activities, which include infrastructure development like underground traffic lines as well as industrial and residential subsurface buildings. In combination with the progressive use of shallow geothermal energy systems, this results in the so-called subsurface urban heat island effect. This article emphasizes the importance of considering the thermal impact of subsurface structures, which commonly is underestimated due to missing information and of reliable subsurface temperature data. Based on synthetic heat-transport models different settings of the urban environment were investigated, including: (1) hydraulic gradients and conductivities, which result in different groundwater flow velocities; (2) aquifer properties like groundwater thickness to aquitard and depth to water table; and (3) constructional features, such as building depths and thermal properties of building structures. Our results demonstrate that with rising groundwater flow velocities, the heat-load from building structures increase, whereas down-gradient groundwater temperatures decrease. Thermal impacts on subsurface resources therefore have to be related to the permeability of aquifers and hydraulic boundary conditions. In regard to the urban settings of Basel, Switzerland, flow velocities of around 1 m d− 1 delineate a marker where either down-gradient temperature deviations or heat-loads into the subsurface are more relevant. Furthermore, no direct thermal influence on groundwater resources should be expected for aquifers with groundwater thicknesses larger 10 m and when the distance of the building structure to the groundwater table is higher than around 10 m. We demonstrate that measuring temperature changes down-gradient of subsurface structures is insufficient overall to assess thermal impacts, particularly in urban areas. Moreover, in areas which are densely urbanized, and where groundwater flow velocities are low, appropriate measures for assessing thermal impacts should specifically include a quantification of heat-loads into the subsurface which result in a more diffuse thermal contamination of urban groundwater resources., Department of Environmental Sciences, Applied and Environmental Geology, University of Basel, Suiza, Agency for Environment and Energy Basel-Stadt, Suiza, Unidad de Zaragoza, Instituto Geológico y Minero de España, España

Many groundwater systems consist of multi-scale aquifer units. The exchange processes and rates between these aquifer units are complex. In order to manage such complex systems, a subdivision into different catchments, sub-catchments or groundwater bodies as manageable units is required. The sustainable management of water resources requires a comprehensive view of water-quality and water-quantity aspects not only for water supply issues, but generally also for flood protection and riverine ecosystem functions. Such transformations require an improved understanding of recharge and exchange processes between different aquifer units as well as aquifer-surface water interaction-processes at different spatiotemporal scales. The main objective of this study is to illustrate concepts by defining the geometry and scales of different aquifer units within a sedimentary basin. The Laufen Basin in the Jura Mountains represents a sub-catchment of the River Birs (Switzerland). Its structure is characterized by a pronounced local relief and a series of aquifer units which are typical for many complex groundwater systems in front of mountain chains such as the alpine foreland and the Jura Mountains of Central Europe. A combination of different concepts is required to understand multi-scale flow systems and to describe the various hydrogeological processes. Three concepts are proposed for the Laufen Basin, including: (1) a regional flow-system analysis, based on the concept of hierarchical groundwater flow systems; (2) the river-corridor concept for understanding aquifer-surface water interaction processes; and (3) the calculation of the dynamic vulnerability index and the aquifer base gradient approach for karst flow and fractured flow systems.

Zusammenfassung: Die Prozesse der Fluss-Grundwasser-Interaktionen sind stark skalenabhängig und im Allgemeinen stark instationär. Einen für das Prozessverständnis wichtigen Aspekt betreffen die kleinräumigen Strömungsverhältnisse an der Grenzschicht zwischen Oberflächengewässer und Grundwasser im hyporheischen Interstitial. Dies betrifft insbesondere auch Fragestellungen zu Strömungsverhältnissen in Forellenlaichgruben kiesführender Flüsse. Exemplarisch für kleinere mit Sohlschwellen verbaute und kanalisierte Fließgewässer wurden am voralpinen Schweizer Fluss Enziwigger verschiedene Methoden entwickelt, getestet und kombiniert, die es erlauben die vier Dimensionen (drei räumliche und eine zeitliche) der Interaktion Oberflächengewässer-Interstitialraum-Grundwasser für einzelne Flussabschnitte zu erfassen. Der Aufbau eines Messnetzes sowie die Durchführung von Feldmessungen lieferten Grundlagen für eine Grundwasserströmungsmodellierung. Kontinuierliche Zeitreihen der Hydraulik, Temperatur und elektrischen Leitfähigkeit im Fließgewässer, an der Gewässersohle sowie im flussnahen Grundwasser dienten zudem der Identifizierung von Zonen mit signifikantem Fluss-Grundwasser-Austausch und von zeitlich instationären bevorzugten Fließpfaden im Grundwasser bei unterschiedlichen hydrologischen Randbedingungen. Die Resultate der Feldmessungen in Kombination mit der instationären Modellierung und Szenarienentwicklung illustrieren die Bedeutung von sich dynamisch verändernden Infiltrations- und Exfiltrationsmustern im Flussbett

Tunnels play a key role in many transportation concepts. The swelling of clay–sulfate rocks leads to serious damage to many tunnels crossing such rock, producing great difficulties and high extra costs in tunnel engineering. The swelling is caused by the transformation of the sulfate mineral anhydrite into gypsum, entailing a 60% volume increase. The transformation involves anhydrite dissolution in water, transport of the solution with groundwater flow, and gypsum precipitation at a different location. Therefore, the knowledge of groundwater flow systems at the tunnel and adjacent areas is essential to better understand the swelling processes. The present study investigates the groundwater flow systems at the Chienberg tunnel in Switzerland before and after the tunnel excavation, based on numerical flow modeling. The models include faults and the hydrostratigraphic layering in the subsurface to assess the role of the hydrogeological setting. The results of this study indicate effects on groundwater flow caused by the tunneling, which may trigger rock swelling by favoring anhydrite dissolution and gypsum precipitation, including (1) increase of flow rates around the tunnel, (2) broadened, shifted and more distributed capture zones leading to a change in origin and age of groundwater, (3) access of groundwater from preferential flow paths (e.g. faults) due to the drainage effect of the tunnel, and (4) change in geochemical equilibrium conditions because of decreased pore water pressures in the tunnel area.

In this study, an approach to estimate the swelling potential of clay-sulfate rocks in tunneling is presented. Swelling of clay-sulfate rocks leads to damage in tunnels that is difficult and costly to repair. Swelling is caused by the transformation of the sulfate mineral anhydrite into gypsum, which involves an increase in rock volume in a system open to water flow. Knowledge of the hydrogeological situation and the groundwater flow systems at the tunnel is essential to better understand the swelling processes. The present study was conducted for the Chienberg tunnel in Switzerland. It investigates the hydrogeological situation of four zones in this tunnel crossing the Triassic Gipskeuper formation. In two of them, heavy swelling occurred after tunnel excavation, while in the other two no swelling occurred. In addition, the groundwater flow systems before and after tunnel excavation are investigated based on numerical flow modeling. The findings suggest that in certain situations after tunnel excavation, depending on geological and changing hydraulic conditions, the excavation damaged zone around the tunnel provides a “hydraulic short circuit” between the weathered Gipskeuper and the anhydrite-bearing strata of the unweathered Gipskeuper. As a result, water from the weathered Gipskeuper gets in contact with anhydrite, triggering its transformation into gypsum and, thus, rock swelling. The results of the study may also contribute to improved swelling experiments in the laboratory and a more reliable planning of restoration measures in tunnels that are damaged by rock swelling.

Theories that describe karst systems are often limited to conceptual models. However, engineering projects within complex karst systems demand the development of tools that allow site-specific descriptions of the hydrogeologic settings and calibrating the processes of karst evolution. Subsidence of a river dam and an adjacent highway, both constructed on gypsum-containing rock, southeast of Basel, Switzerland, required remedial construction measures. A monitoring network was set up, to safeguard surface and subsurface water resources during the construction measures. The primary project goal was to develop tools that enable a continuous characterization of the groundwater flow regime and that facilitate the evaluation of the long-term performance of the infrastructures. Investigative methods included high-resolution 3D hydrogeological modeling, and the integration of geological, hydrometrical and hydrogeophysical field data of varying quality. Particular focus was placed on the hydraulic behavior of the complex conduit system. Results help to understand the evolution of distinct karst features and zones of preferential flow. The location of fracture zones and parts of the old meandering river course, playing a major role in the karst evolution process, could be identified. Together with the hydrometrical investigations and hydrogeological modeling, the evolution of the karst system and its dynamics can be interpreted in relation to the groundwater flow regime.

We use the gradient of the aquifer base to investigate the hydrology of mature, shallow karst systems. We first present a 3D geological model of the Gempen plateau (NW Switzerland) that reveals the geometry of aquifers and aquitards and their displacement at faults, then transfer the 3D geological model to a hydrological model. The transformation is based on a conceptual karst model approximating subsurface flow in mature, shallow karst systems to open surface flow on the top of the uppermost aquitard or aquifer base. The gradient of this surface is expected to mainly influence regional groundwater flow patterns. We use the hydrological model to delineate spring catchment areas. The discharge areas and corresponding catchment areas of the model are compared with the occurrence of springs in the study area and with hydraulic links confirmed by tracer tests. We also describe the way in which the hydrological model contributes to identifying flow processes. The proposed aquifer base gradient approach enhances vulnerability assessment in mature, shallow karst regions by (1) localizing catchment areas as a precondition of source protection strategies and (2) indicating dominant flow processes associated with individual springs.

A 3D geological model of the area east of Basel on the southeastern border of the Upper Rhine Graben, consisting of 47 faults and six stratigraphic horizons relevant for groundwater flow, was developed using borehole data, geological maps, geological cross sections, and outcrop data. This model provides new insight into the discussions about the kinematics of the area between the southeastern border of the Upper Rhine Graben and the Tabular Jura east of Basel. A 3D analysis showed that both thin-skinned and thick-skinned tectonic elements occur in the modeled area and that the Anticline and a series of narrow graben structures developed simultaneously during an extensional stress-field varying from E–W to SSE–NNW, which lasted from the Middle Eocene to Late Oligocene. In a new approach the faults and horizons of the 3D geological model were transferred into discrete elements with distributed hydrogeological properties in order to simulate the 3D groundwater flow regime within the modeled aquifers. A three-layer approach with a horizontal regularly spaced grid combined with an irregular property distribution of transmissivity in depth permitted the piezometric head of the steady-state model to be automatically calibrated to corresponding measurements using more than 200 piezometers. Groundwater modeling results demonstrated that large-scale industrial pumping affected the groundwater flow field in the Upper Muschelkalk aquifer at distances of up to 2 km to the south. The results of this research will act as the basis for further model developments, including salt dissolution and solute transport in the area, and may ultimately help to provide predictions for widespread land subsidence risks.

This paper describes two groundwater models simulating a well capture zone in a heterogeneous aquifer located near an infiltrating river. A deterministic, large-scaled groundwater model (1.8 × 1.2 km) is used to simulate the average behavior of groundwater flow and advective transport. It is also used to assign the boundary conditions for a small-scaled groundwater model (550 × 400 m) which relies on stochastically generated aquifer properties based on site-specific drill core and georadar data. The small-scaled groundwater model is used to include the large subsurface heterogeneity at the location of interest. The stochastic approach in the small-scaled groundwater model does not lead to a clearly defined well capture zone, but to a plane representation of the probability of a certain surface location belonging to the well capture zone. The models were applied to a study site, which is located in an area of artificial groundwater recharge and production, in Lange Erlen near Basel, Northwestern Switzerland. The groundwater at this site contributes to the city’s drinking water supply, and the site serves as a recreational area to the population of Basel. The river is channelized, but there are initiatives to restore the riverbank to more natural conditions. However, they conflict with the requirements of groundwater protection, especially during flood events. Therefore, a river section of 600 m in the vicinity of an unused and disconnected drinking water well was restored to study changes in the groundwater flow regime depending on hydrologic variations, water supply operation data, progress of river restoration, and subsurface heterogeneity. The results of the groundwater models are compared with data from two tracer experiments using Uranine and the natural Radon isotope Rn-222, and with physical, chemical, and microbiological data sampled in monitoring wells between the river and the drinking water well. The groundwater models document significant variations regarding the dimension of the well capture zone depending on changing boundary conditions and the variability of the hydraulic aquifer properties. The knowledge of the subsurface heterogeneity is important to evaluate transport times and distances of microorganisms from the infiltrating river or the riverbank to the drinking water well. The data from the monitoring wells show that chemical and microbiological processes predominantly occur in the hyporheic interstitial zone and the riverbank within a range of a few meters up to a few 10s of meters from the river. The methods presented here can be used to define and evaluate groundwater protection zones in heterogeneous aquifers associated with infiltration from rivers under changing boundary conditions, and under the uncertainty of subsurface heterogeneity. Furthermore, they allow one to study the site-specific operational alternatives associated with river restoration.

Pollution in the shallow subsurface has led to an increasing need of understanding how to quantitatively characterize both the heterogeneity of gravel aquifers and the influence of heterogeneity on groundwater flow and solute transport. Models play an important role in decision-making processes, especially in the context of better characterizing and in forecasting the behavior of a given geological system. The objective of the present paper is the derivation of a gradual lithofacies-based interpretation of outcrop, drill core, and ground penetrating radar (GPR or georadar) data of different quality. The presented method allows a probability estimation of drill core layer descriptions and radarfacies types representing defined sedimentary structure types. The method includes a determination of ‘initial structure type probabilities’ for grain-size categories and combinations thereof described in drill core layer descriptions as well as a subsequent differentiation of these structure type probabilities in an iterative process considering ‘additional information’ like main constituent, quantity, fraction, and sorting of single grain-size categories, color, chemical precipitation, layer thickness, and adjacent layer. The radarfacies types are calibrated with drill cores located in the vicinity of georadar sections. The calibration process consists of the assignment of the calculated structure type probabilities from the drill core layer descriptions to the corresponding radarfacies types considering the proportion in thickness between drill core layers and georadar structures. The structure type probabilities can be given for points along boreholes and a grid with arbitrary mesh size along georadar sections. The method is applied to field examples from the Rhine/Wiese aquifer near Basel in Switzerland. The resulting structure type probabilities can be used for conditioning stochastic simulations of geological models. However, the conditioned stochastic simulation of the Rhine/Wiese aquifer is the topic of another paper. The results show the importance of a detailed sedimentological analysis of outcrops and drill cores as well as its significance on the distinction of sedimentary structure types.

Groundwater circulation in evaporite bearing horizons and the resulting evolution of karst frequently causes geotechnical problems such as land subsidence or collapses. Even comparably small subsidence rates can significantly affect sensitive urban infrastructure. Dissolution of deep-seated evaporites occurs when groundwater, undersaturated with respect to highly soluble minerals, enters into contact with an evaporite body. Groundwater can interact from all directions in space. Laboratory dissolution experiments were carried out to study the effect of freshwater in contact with rock salt, accounting for the effect of dipping interfaces as an abstraction of inclined geological formations. The dissolution experiments were carried out both in 2D and 3D. The approach allows studying dissolution in a normal fault juxtaposing a developing intrastratal salt karst against a salt layer or against a poorly soluble layer. Modeling experiments were conducted to study the effect of variable density flow in inclined aquifers bordering halite formations and the effect of different fault geometries. The numerical simulations of density driven flow were evaluated along 1,000 m long and 150 m deep 2D cross sections to study the effect of tectonic horst and graben structures. Results show that a large fault zone consisting of a set of smaller hydraulically higher conductive faults is a major factor for dissolution.

More than 30% of Europe's land surface is made up of karst exposures. In some countries, water from karst aquifers constitutes almost half of the drinking water supply. Hydrological simulation models can predict the large-scale impact of future environmental change on hydrological variables. However, the information needed to obtain model parameters is not available everywhere and regionalisation methods have to be applied. The responsive behaviour of hydrological systems can be quantified by individual metrics, so-called system signatures. This study explores their value for distinguishing the dominant processes and properties of five different karst systems in Europe and the Middle East. By defining ten system signatures derived from hydrodynamic and hydrochemical observations, a process-based karst model is applied to the five karst systems. In a stepwise model evaluation strategy, optimum parameters and their sensitivity are identified using automatic calibration and global variance-based sensitivity analysis. System signatures and sensitive parameters serve as proxies for dominant processes, and optimised parameters are used to determine system properties. By sensitivity analysis, the set of system signatures was able to distinguish the karst systems from one another by providing separate information about dominant soil, epikarst, and fast and slow groundwater flow processes. Comparing sensitive parameters to the system signatures revealed that annual discharge can serve as a proxy for the recharge area, that the slopes of the high flow parts of the flow duration curves correlate with the fast flow storage constant, and that the dampening of the isotopic signal of the rain as well as the medium flow parts of the flow duration curves have a non-linear relation to the distribution of groundwater storage constants that represent the variability of groundwater flow dynamics. Our approach enabled us to identify dominant processes of the different systems and provided directions for future large-scale simulation of karst areas to predict the impact of future change on karst water resources.

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 downgradient 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. Hydrogeologie der Nordwestschweiz, Grundwasser in Basel

[1] Swelling of clay-sulfate rocks is a major threat in tunneling. It is triggered by the transformation of the sulfate mineral anhydrite into gypsum as a result of water inflow in anhydrite-containing layers after tunnel excavation. The present study investigates the hydraulic effects of tunneling on groundwater flow and analyzes how hydraulic changes caused by excavation lead to water inflow into anhydrite-containing layers in the tunnel area. Numerical groundwater models are used to conduct scenario simulations that allow one to relate hydrogeological conditions to rock swelling. The influence of the topographic setting, the excavation-damaged zone around the tunnel, the sealing effect of the tunnel liner, and the geological configuration are analyzed separately. The analysis is performed for synthetic situations and is complemented by a case study from a tunnel in Switzerland. The results illustrate the importance of geological and hydraulic information when assessing the risk of swelling at an actual site.

Summary Describing the complex structures that exist in many sedimentary aquifers is crucial for reliable groundwater flow and transport simulation. However, hardly any aquifer can be inspected in such detail that all decimeter to meter heterogeneity is resolved. Aquifer analogs serve as surrogates to construct models of equivalent heterogeneity, and thus imitate those features relevant for flow or transport processes. Gravel pits found in excavation show excellent sections of the sedimentary sequence and thus offer direct insight into the structural and textural composition of the subsoil. This paper describes an approach to also inspect the third dimension: by mapping during the ongoing excavation it is possible to obtain a three-dimensional representation of the subsurface within a short period of time. A detailed description of a case study is presented and the findings from sedimentological, hydrogeological and geophysical analyses are compared. The gravel pit is located near the town of Herten in southwest Germany, where relatively young unconsolidated fluvio-glacial and fluvial sediments in the Rhine basin are mined. The excavated gravel body is built up by architectural elements typical for braided river deposits. The study generated a high-resolution data set of lithofacies, hydrofacies and ground penetrating radar (GPR) profiles. It represents the basis for a full three-dimensional geostatistical reconstruction presented in the second part ( Comunian et al., 2011 ).

Generally open space in urban areas is very rare. Therefore, the subsurface is used more frequently for the growth of city infrastructure and traffic lines. Such constructions can temporarily affect urban groundwater systems during the construction period and permanently after completion. Subsurface constructions inevitably increase the pressure on urban groundwater resources and often result in a reduction of cross-sectional groundwater flow and aquifer-storage capacities.

Braided river deposits form important aquifers in many parts of the world, and their heterogeneity strongly influences groundwater flow and mass transport processes. To accurately characterize these coarse gravelly aquifers, it is important to understand the erosional and depositional processes that form these sediments. Moreover, it is important to evaluate the relative importance of various parameters that determine the preservation potential of different depositional elements over geological time scales. These objectives may be achieved by developing techniques that allow for the integration of different quality data into quantitative models. Information concerning sedimentary textures and the spatial continuity of sedimentary structures in braided river deposits, inherent in depositional facies descriptions, allows the spatial variability of hydrogeological properties (e.g. hydraulic conductivity and porosity) to be predicted. Depositional elements in gravel deposits can contain a restricted range of textures, which form a limited number of sedimentary structures. These depositional elements are bounded by erosional and/or lithological surfaces. The frequency, size and shape of different elements in a sedimentary sequence depend on several factors, including aggradation rate, channel belt mobility on the kilometre scale, gravel-sheet/scour activity at the scale of hundreds of metres and topographic position of the different elements within an evolving system. Preserved shape and size of the elements affect the correlation lengths and the standard deviations of the aquifer properties, such as hydraulic conductivity and porosity. Different quality data sets that may be used in characterizing braided river deposits can be recognized in outcrop, boreholes and on ground-penetrating radar (GPR) sections. This paper proposes a means of integrating outcrop, borehole and GPR data into a stochastic framework of sedimentary structures and the distribution of hydraulic aquifer properties. Data integration results in variable degrees of uncertainty when assigning values to hydraulic properties and characterizing the geometry of sedimentary structures. An application of this approach is illustrated using a data set (400 m × 550 m) from the northeastern part of Switzerland at the confluence of the Rhine and Wiese rivers. The data set includes drill-core data from five boreholes and 14 GPR sections with a total length of 3040 m. The results of the variogram analysis provide the orientation of sedimentary structure types representing the main flow direction of the River Rhine in the lower part of the aquifer, and of the River Wiese in the upper part. The analysis also results in large ranges of spatial correlation, ranging from a few metres up to tens of metres for the different sedimentary structure types.

The objective of this work is to facilitate a sustainable regional planning of water resources in karst areas by providing a conceptual framework for an integrative vulnerability assessment. A combined mapping and modeling approach is proposed, taking into account both spatial and temporal aspects of karst groundwater vulnerability. The conceptual framework comprises the delineation of recharge areas, vulnerability mapping, numerical flow and transport modeling and the integration of information into a combined vulnerability map and time series. The approach is illustrated at a field site in northwest Switzerland (Gempen plateau). The results show that the combination of vulnerability mapping and numerical modeling allows the vulnerability distribution, both in the recharge and discharge areas, to be identified, and at the same time, the time dependence of karst groundwater vulnerability to be assessed. The combined vulnerability map and time series provide a quantitative basis for drinking water management and for regional planning.

During the past decade significant progress has been made in the development of geophysical techniques designed to resolve problems associated with the unconsolidated sedimentary layers of the shallow subsurface. Two of these techniques, the high-resolution seismic reflection and the ground-penetrating radar (georadar) methods, have the potential to define the character, size, and geometry of surficial sedimentary units. In an attempt to determine optimum recording and processing strategies, seismic and gwradar reflection profiles have been recorded across a variety of glacial, glaciolacustrine, and glaciofluvial deposits in Switzerland. At one test location we have also conducted a pilot 3-D high-resolution seismic reflection survey and at another we have collected an experimental 3-D gwradar data set. Results of the 3-D surveys are striking images of the shallow subsurface that provide many more details and much more reliable information on the 3-D heterogeneities of the shallow subsurface than are afforded by conventional 2-D data sets; at both 3-D test sites critical geological features would have been misinterpreted had only limited profile information been available. INTRODUCTION Mankind is placing increasing demands on the surficial geology in formerly glaciated terranes in connection with groundwater, resource exploration and engineering (including waste disposal) activities. Switzerland’s vast glacial and glaciofluvial deposits contain more than two-thirds of the country’s aquifers and include large concentrations of industrial minerals (e.g. sand and gravel). Because the most densely populated centres are built upon these unconsolidated deposits, the underlying groundwater aquifers are susceptible to contamination from chemical spills, leaky waste disposal sites and polluted rivers. It is well known that groundwater flow is influenced strongly by the nature of the surficial geology (i.e. the distribution of lithofacies) and recent investigations have shown that predictions of contaminant transport require reliable information on the 3-D distributions of the highly permeable sedimentary units. Sands and gravels have by far the highest hydraulic conductivities, so knowledge of their distribution and physical characteristics is key to an improved understanding of groundwater transport and containment. Variations of glacial lithofacies and associated order-of-magnitude changes of hydraulic conductivity may occur over such short distances that even a relatively dense network of boreholes and outcrops may not resolve the geometries and sizes of the different geological units the information would be “spatially aliased”. The task for engineering and environmental geophysicists is to further develop non-invasive and non-destructive methods that allow the character (lithofacies), size, geometry and 3-D distribution of important unconsolidated sedimentary units to be determined. As a contribution to this goal, high-resolution seismic and georadar reflection data have been recorded across a variety of Swiss glacial deposits. In this paper we describe preliminary results of the following: n high-resolution 2-D and 3-D seismic reflection surveys conducted across a sequence of till and ouhvash overlying glaciolacustrine sediments (Stetten survey area); H high-resolution seismic reflection profiling performed over end moraine sediments (Suhretal survey area); n 2-D and 3-D georadar surveys conducted across glaciofluvial sediments (Rafzerfeld survey area).