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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.

Groundwater extracted from alluvial aquifers close to rivers is vulnerable to contamination by infiltrating river water. Infiltration is often increased during high discharge events, when the levels of waterborne pathogens are also increased. Water suppliers with low-level treatment thus rely on alternative measures derived from information on system state to manage the resource and maintain drinking-water quality. In this study, a combination of Self-Organizing Maps and Sammon’s Mapping (SOM-SM) was used as a proxy analysis of a multivariate time-series to detect critical system states whereby contamination of the drinking water extraction wells is imminent. Groundwater head, temperature and electrical conductivity time-series from groundwater observation wells were analysed using the SOM-SM method. Independent measurements (spectral absorption coefficient, turbidity, particle density and river stage) were used. This approach can identify critical system states and can be integrated into an adaptive, online, automated groundwater-management process.

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.

The genesis of alternate gravel bars in straightened rivers and braided rivers is closely coupled to the formation of scours. Scours can lead to riverbank failure, initiate lateral river dynamics and strongly impact the interaction between surface and subsurface flow and transport. It is, therefore, critical to account for scours in the design of flood protection measures. However, there is still little knowledge on the formation and characteristics of such scours, especially on the dynamic relationship between the riverbed morphology and the scours. Bathymetric riverbed surveys conducted at medium to low discharge may underestimate the real scour sizes and shapes if scours filled with sediments during waning discharge. Furthermore, the literature suggests that gravel bars and scours can jointly migrate on the riverbed, resulting in cut‐and‐fill sedimentary structures in the near subsurface. These cut‐and‐fill structures cannot be observed from the surface. We investigate with ground‐penetrating radar the presence of scour fills below the riverbed of two gravel‐bed rivers and study any indications of bar and scour migration. Thus, two ground‐penetrating radar surveys were conducted, one on the emerged part of an alternate bar of the channelized Alpine Rhine River (Switzerland) and the other on a flat gravel surface in a braided reach of the Tagliamento River (Italy) that is near the pristine state. At both sites, a scour fill could be clearly identified below a 2‐m‐thick sediment layer. The imaged part of the scour of the Alpine Rhine River (30 × 100 × 4.5 m) is located at the front end of the gravel bar next to the riverbank. This scour was only partially imaged by ground‐penetrating radar and is in reality significantly deeper and larger. The scour of the Tagliamento River (20 × 30 × 2.5 m) shows a clear internal structure consisting of inclined, planar cross‐beds that merge tangentially with the lower‐bounding erosional surface of the scour. At the light of the literature, we compare these two scours in terms of sedimentary processes resulting from the complex interplay between scours and gravel bars. The study findings offer a promising research avenue on the dynamic relationship between discharge, sediment transport, scour and bar formation and migration.

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.

As open space in urban areas is very rare and mobility requirements are constantly increasing, new infrastructures are being planned and constructed in the subsurface. These underground infrastructures may additionally be used as Shallow Geothermal Energy systems (SGE) to exchange and store heat. For real-world tunnel set-ups in the urban agglomeration of Basel (Switzerland), optimal closed and open SGE systems were evaluated depending on the type of tunnel infrastructure (motorway or railway) as well as geological and hydrogeological settings. This contribution illustrates strategies for seasonal Thermal Energy Storage (TES) in solid rock layers at depth of approx. 25 and 35 m by combination of Tunnel Absorber Segments (TAS), and very shallow Borehole Heat Exchangers (BHE). Investigations focus on the efficiency of the TES systems where the BHE extracts heat injected by TAS. First results suggest that thermal energy of up to 290 W could be recovered by the simulated double-U-loop BHE. Furthermore, TES system efficiency can reach values of up to 10.2%. The here presented performance analysis provides preliminary evaluation elements of SGE combined use as a further step for spatiotemporal thermal management in realistic urban settings.

(IF 6.44; Q1); International audience; Karst aquifers provide drinking water for 10% of the world’s population, support agriculture, groundwater-dependent activities, and ecosystems. These aquifers are characterised by complex groundwater-flow systems, hence, they are extremely vulnerable and protecting them requires an in-depth understanding of the systems. Poor data accessibility has limited advances in karst research and realistic representation of karst processes in large-scale hydrological studies. In this study, we present World Karst Spring hydrograph (WoKaS) database, a community-wide effort to improve data accessibility. WoKaS is the first global karst springs discharge database with over 400 spring observations collected from articles, hydrological databases and researchers. The dataset’s coverage compares to the global distribution of carbonate rocks with some bias towards the latitudes of more developed countries. WoKaS database will ensure easy access to a large-sample of good quality datasets suitable for a wide range of applications: comparative studies, trend analysis and model evaluation. This database will largely contribute to research advancement in karst hydrology, supports karst groundwater management, and promotes international and interdisciplinary collaborations.

Karst aquifers provide drinking water for 10% of the world’s population, support agriculture, groundwater-dependent activities, and ecosystems. These aquifers are characterised by complex groundwater-flow systems, hence, they are extremely vulnerable and protecting them requires an in-depth understanding of the systems. Poor data accessibility has limited advances in karst research and realistic representation of karst processes in large-scale hydrological studies. In this study, we present World Karst Spring hydrograph (WoKaS) database, a community-wide effort to improve data accessibility. WoKaS is the first global karst springs discharge database with over 400 spring observations collected from articles, hydrological databases and researchers. The dataset’s coverage compares to the global distribution of carbonate rocks with some bias towards the latitudes of more developed countries. WoKaS database will ensure easy access to a large-sample of good quality datasets suitable for a wide range of applications: comparative studies, trend analysis and model evaluation. This database will largely contribute to research advancement in karst hydrology, supports karst groundwater management, and promotes international and interdisciplinary collaborations., Measurement(s)hydrographic feature • fluid flow rateTechnology Type(s)digital curationFactor Type(s)geographic location • yearSample Characteristic - Environmentkarst • spring • groundwater Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.11336507

The presented study explores the salt dissolution potential of fluids around a salt diapir in the Transylvanian town of Ocna Mures, Romania, which is facing land-collapse hazards related to salt mining activities. A structural three-dimensional (3D) model of the salt diapir, the adjacent basin sediments, and the mining galleries was developed based on existing maps, borehole data, own field observations, and geological publications of the Transylvanian Basin. The salt dissolution potential was estimated from 2D vertical thermohaline flow and transport model scenarios along the southeastern flank of the diapir. Results showed that the following factors increase the salt dissolution capacity along the upper 180 m of the diapir: (1) the presence of more permeable Quaternary alluvial sediments in connection with a fault zone of higher permeability along the diapir, and (2) the presence of more permeable sandstone units within the Miocene sediments in the east of the diapir, which provide freshwater access to the upper parts of the diapir. Thermohaline simulation with viscosity variation of the fluid, instead of a constant viscosity, influences the resulting salt fluxes by up to 50% within studied temperature ranges of 10-60 °C in the model domain. The range of theoretical dissolution rates along the upper 180 m of the diapir supports the hypothesis that cavern collapse is more likely to occur where cavern side walls have already been mined to almost no remaining side walls of rock salt, which is the case in the southeastern part of the diapir.

The reliable characterization of heterogeneous sedimentary aquifers, especially the identification of preferential flow paths and their connectivity remains a challenge in applied hydrogeology research and practice. However, aforementioned information is crucial for predicting subsurface flow and contaminant transport in complex deposits. Well established characterization methods such as outcrop analogue studies, hydraulic tomography, tracer testing, and direct push profiling suffer from uncertainty due to non-uniqueness of underlying inversions or insufficient temporal and/or spatial data resolution. Furthermore, the relation and effects of observed heterogeneity in hydraulic conductivity on transport is not always straight forward.A promising novel approach to overcome the limitations of conventional hydraulic site characterization techniques is the joint application of tracer testing and direct push logging. We present a proof-of-concept field study, where conventional salt tracer testing was combined with vertical high resolution direct push electrical conductivity profiling. The method successfully captured tracer distribution in heterogeneous sedimentary deposits in-situ and visualized measured tracer distribution over time. Additional measurements, such as breakthrough-curves and surface geophysics can be easily integrated to set up ex-post simulations to further increase site-specific understanding of groundwater flow and transport processes.

The presented study estimates salt dissolution caused by groundwater around a salt diapir in the Transylvanian Basin, which is facing land-collapse hazards related to historic salt mining activities. Because the amount of salt dissolution is controlled by the concentration gradients and fluxes near vulnerable areas of the salt dome, specific attention has been given to hydrogeological boundary conditions. They include the hydraulic role of possible more permeable fault zones along the salt dome, and the potential access to the salt diapir of over-pressurized subsaturated groundwater within regional scale sandstone layers. A structural three-dimensional (3D) model of the salt diapir, the adjacent basin sediments, and the mining galleries was developed based on existing maps, borehole data, own field observations, and geological publications of the Transylvanian Basin. The salt dissolution potential was simulated with 2D vertical thermohaline flow and transport model scenarios along the southeastern flank of the diapir. Results showed that the following factors increase the salt dissolution capacity along the upper 180 m of the diapir: (1) the presence of more permeable Quaternary alluvial sediments in connection with a fault zone of higher permeability along the diapir, and (2) the presence of more permeable sandstone units within the Miocene sediments in the east of the diapir, which provide freshwater access to the upper parts of the diapir. Thermohaline simulation with viscosity variation of the fluid, instead of a constant viscosity, influences the resulting salt fluxes by up to 50% within studied temperature ranges of 10 to 60°C in the model domain. The range of theoretical dissolution rates along the upper 180 m of the diapir supports the hypothesis that cavern collapse is more likely to occur where cavern side walls have already been mined to almost no remaining side walls of rock salt, which is the case in the southeastern part of the diapir. A past land collapse from 2010, which formed a 70-90 m wide saline lake, has occurred in this area southeast of the diapir appearing to be the more vulnerable to land collapse.Zechner, E., Dresmann, H., Mocuţa, M., Danchiv, A., Huggenberger, P., Scheidler, S., Wiesmeier, S., Popa, I., Zlibut, A. (2019): Salt dissolution potential estimated from two-dimensional vertical thermohaline flow and transport modeling along a Transylvanian salt diapir, Romania, Hydrogeol. J., 27, 1245-1256, https://doi.org/10.1007/s10040-018-1912-1.

Im Wassergewinnungsgebiet Hardwald werden rund 15 Mio. m3/a Trinkwasser produziert. Es finden sich jedoch Spuren von chlorierten organischen Verbindungen im Grundwasser. Als Fallstudie werden hier die Ergebnisse von Feld- und Laborarbeiten zur Bestimmung der raumlichen Verteilung der chlorierten organischen Verbindungen, der stabilen Wasserisotope (δ18O und δ2D), der Hauptkationen- und -anionen und ausgewahlter Spurenstoffe, welche uber ein Rheininfiltrat eingetragen werden, vorgestellt. Als Ergebnis der Untersuchungen zeigte sich, dass die kunstliche Rheinwasserinfiltration ganz entscheidend zur Trinkwassersicherheit beitragt und das entnommene Grundwasser vorwiegend der chemischen Signatur des infiltrierten Rheinwassers entspricht. Jedoch zeigt sich auch, dass durch die uber die Flache ungleichmasig verteilte Infiltration vor allem eine Beimischung von Muschelkalkwasser in sud-westlichen Bereichen des Untersuchungsgebiets wahrscheinlich ist. Diese Interpretation wird durch die Verteilung der chlorierten organischen Verbindungen, Hauptkationen- und -anionen, stabilen Wasserisotopen und Spurenstoffen gestutzt. Trotz der hier vorhandenen komplexen Randbedingungen wird durch das Zusammenspiel von kunstlicher Infiltration und Entnahme eine sichere Trinkwasserversorgung ermoglicht.

To sustainably plan the use of subsurface resources, a discussion about thermal management is needed, as well as a more coordinated and efficient thermal use of subsurface resources. This contribution outlines a theoretical consideration for how to effectively manage urban subsurface resources. The consideration is made by means of assessing the heat-potential from urban groundwater resources against the background of heat-demand. We illustrate that, in principle, the heat-potential of subsurface resources could be directly ‘mined’ to exploit them and store thermal ‘waste energy’. We show how quantitative flow- and heat-transport modeling approaches can offer a scientific basis for thermal management strategies. In combination with geographic information systems, evaluating heat-potential and heat-demand can become the basis for management concepts as well as for the overall economic and ecological thermal planning of subsurface resource usage. An index which relates groundwater heat-potential to heat-demand is introduced here. This index allows us to quantify the share that thermal ‘waste energy’ from groundwater resources could have to satisfy heat-demand. On the one hand, we demonstrate how the spatial distribution of this index can be derived for the urban area of Basel, Switzerland. On the other hand, we exemplify the temporal evolution of the heat-potential for selected urban areas and discuss the capacity for space heating with a typical annual heat-demand profile.

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.

As a result of the increasing use of shallow geothermal resources, hydraulic, thermal and chemical impacts affecting groundwater quality can be observed with ever increasing frequency (Possemiers et al., 2014). To overcome the uncertainty associated with chemical impacts, a city scale study on the effects of intensive geothermal resource use by groundwater heat pump systems on groundwater quality, with special emphasis on heavy metal contents was performed. Statistical analysis of geochemical data obtained from several field campaigns has allowed studying the spatiotemporal relationship between temperature anomalies in the aquifer and trace element composition of groundwater. The relationship between temperature and the concentrations of trace elements resulted in weak correlations, indicating that temperature changes are not the driving factor in enhancing heavy metal contaminations. Regression models established for these correlations showed a very low reactivity or response of heavy metal contents to temperature changes. The change rates of heavy metal contents with respect to temperature changes obtained indicate a low risk of exceeding quality threshold values by means of the exploitation regimes used, neither producing nor enhancing contamination significantly. However, modification of pH, redox potential, electrical conductivity, dissolved oxygen and alkalinity correlated with the concentrations of heavy metals. In this case, the change rates of heavy metal contents are higher, with a greater risk of exceeding threshold values.

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.

The objective of this study is the introduction of an optimum model extent in discontinuous rock masses for tunnel inflow assessment using numerical models. Tunnel groundwater inflow is an important problem in tunneling, and numerical simulation is widely used for estimating the amount of tunnel inflow. An adequate size of the model domain is of very high importance when using such models. On the one hand, if the tunnel boundary is too close to the outer model boundary, the simulated inflow rate into the tunnel is significantly overestimated (which will be shown in the present study). On the other hand, if the model domain is very large, models may become “unhandy”, and simulations become very expensive with respect to computer memory and CPU. In this technical note, an approach is presented that derives an optimum model extent for numerical simulation of tunnel inflow in fractured rock. The approach uses the two-dimensional universal distinct element code (UDEC). The impact of different model parameters, such as tunnel radius, groundwater level, joint spacing, joint dip/dip direction and joint aperture on the optimum model extent has been evaluated. Based on the results, an optimum model extent chart is presented that allows modelers a quick determination of the optimum model extent as a function of the most significant parameters, which are the tunnel depth under the groundwater level, tunnel radius and joint spacing.

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.

Heating and cooling using groundwater is often performed without considering potential effects on subsurface resources and the multiple interactions of different subsurface utilizations. As a result, significantly increased subsurface temperatures have been observed in many urban areas. The current uncoordinated use of subsurface resources can lead to conflicts among different users and, specifically thermal pollution may lead to large-scale thermal impacts and impairments of groundwater quality.

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.

Journal of Seismology, 10 (4), ISSN:1383-4649, ISSN:1573-157X

Zusammenfassung: Der Nutzungsdruck auf Grundwasserressourcen in intensiv genutzten Flussebenen wird zunehmend größer. Ziel dieses Beitrages ist, anhand eines repräsentativen, instationären Datensatzes eines urbanen Grundwassersystems (Unteres Birstal CH) aufzuzeigen, wie mit Ansätzen des adaptiven Grundwassermanagements die Voraussetzungen für die nachhaltige Nutzung von Grundwasserressourcen geschaffen werden können. Mithilfe eines instationären Grundwassermodells können spezifische Fragen der Fluss-Grundwasser-Interaktion und dem Betrieb künstlicher Grundwasseranreicherung beantwortet werden. Die Instationarität der Fluss-Grundwasser-Interaktion und eine damit zusammenhängende Änderung von In - und Exfiltrationsverhältnissen konnte für verschiedene Flussabschnitte ermittelt werden. Die Datenauswertung eines Jahrhunderthochwassers trug wesentlich zum Verständnis dieser Prozesse bei. Durch ein Experiment mit der längerfristigen Außerbetriebnahme einer künstlichen Grundwasseranreicherung im Untersuchungsgebiet konnten die Auswirkungen von geplanten Nutzungsänderungen abgeschätzt werden. Die Untersuchungen tragen zum Prozessverständnis des Grundwassersystems bei und liefern die Grundlage für eine Diskussion über lang-, mittel- und kurzfristige Ziele hinsichtlich der regionalen Bewirtschaftung urbaner Wasserressourcen

Faecal contamination of drinking water extracted from alluvial aquifers can lead to severe problems. River water infiltration can be a hazard for extraction wells located nearby, especially during high discharge events. The high dimensionality of river–groundwater interaction and the many factors affecting bacterial survival and transport in groundwater make a simple assessment of actual water quality difficult. The identification of proxy indicators for river water infiltration and bacterial contamination is an important step in managing groundwater resources and hazard assessment. The time resolution of microbial monitoring studies is often too low to establish this relationship. A proxy-based approach in such highly dynamic systems requires in-depth knowledge of the relationship between the variable of interest, e.g. river water infiltration, and its proxy indicator. In this study, continuously recorded physico-chemical parameters (temperature, electrical conductivity, turbidity, spectral absorption coefficient, particle density) were compared to the counts for faecal indicator bacteria, Escherichia coli and Enterococcus sp. obtained from intermittent sampling. Sampling for faecal indicator bacteria was conducted on two temporal scales: (a) routine bi-weekly monitoring over a month and (b) intense (bi-hourly) event-based sampling over 3 days triggered by a high discharge event. Both sampling set-ups showed that the highest bacterial concentrations occurred in the river. E. coli and Enterococcus sp. concentrations decreased with time and length of flow path in the aquifer. The event-based sampling was able to demonstrate differences in bacterial removal between clusters of observation wells linked to aquifer composition. Although no individual proxy indicator for bacterial contamination could be established, it was shown that a combined approach based on time-series of physico-chemical parameters could be used to assess river water infiltration as a hazard for drinking water quality management.

In straight gravel-bed river reaches, riverbank erosion can be induced by alternate bars and their associated scours. The maximum scour depth is therefore a key information to design reliable flood protections. However, scour depth cannot be correctly assessed by bathymetric riverbed surveys if scours are filled with sediments at low discharge. In this work, scour depths in a straightened, gravel-bed river with alternate bars is quantified with ground-penetrating radar (GPR) and the riverbed morphology is linked to the subsurface structure. A 4.5 m deep buried scour with an extent of 30 × 100 m is partially imaged by GPR at the front end of the gravel bar next to the riverbank. The non-imaged part of the scour is expected to be much larger and therefore deeper. Additional research is needed to assess how scour location and depth relate with discharge magnitude and gravel bar dynamics.

In order to understand heterogeneity distribution of hydraulic properties, many studies have proposed models of coarse, braided river deposits. However, they often focus either on the surface/near surface or on ancient deposit analysis. Furthermore, the link between morphological (surface) and sedimentological (outcrops) information has not been fully explored yet. This publication aims to characterize the morphodynamics of a braided, gravel-bed reach of the Tagliamento River (NE Italy) and to assess its relationship with the subsurface heterogeneity. The morphological analysis is based on a LiDAR-derived DEM, aerial and satellite photographs from 1998 to 2011, as well as field observations. A water-stage time series allows the morphological changes to be related to the discharge dynamics. The sedimentological knowledge on coarse, braided deposits was mainly gained from the observation of analog Pleistocene coarse deposits in Switzerland. The main geomorphological elements are identified in terms of their topographic signature and genesis, setting apart the trichotomy water–vegetation–bar. The braidplain is characterized by higher-lying zones with dentritic gully drainage networks and active zones where most of the morphology reworking occurs. Furthermore, two morphologies mark the active zones: a low-discharge morphology (low-discharge incisions and channels, slip-face lobes, etc.) superimposed on a high-discharge morphology (gravel sheets, scours, etc.). Each morphological element is related to a depositional (i.e., sedimentological) element whose preservation potential in the subsurface is assessed as a function of the river-bed aggradation dynamic. The settings that impact the subsurface flow in terms of fast pathway and connectivity are addressed.

Hydrogeologist are commonly confronted to field data scarcity. An interesting way to compensate this data paucity, is to use analog data. Then the questions of prediction accuracy and uncertainty assessment when using analog data shall be raised. These questions are investigated in the current paper in the case of contaminant transport forecasting in braided river aquifers. In using analog data from the literature, multiple unconditional geological realizations are produced following different geological conceptual models (Multi-Gaussian, Object-based, Pseudo-Genetic). These petrophysical realizations are tested in a contaminant transport problem based on the MADE-II tracer experiment dataset. The simulations show that reasonable contaminant transport predictions can be achieved using analog data. The initial concentration conditions and location regarding the conductivity heterogeneity field have a stronger influence on the plume behavior than the resulting equivalent permeability. The results also underline the necessity to include a wide variety of geological conceptual models and not to restrain parameter space exploration within each concept as long as no field data allows for conceptual model or parameter value falsification.

International audience; A new benchmark is proposed for the verification of buoyancy-driven flow codes. The benchmark deals with mixing hot and cold fluids from the opposite boundaries of an open channel. A high accurate solution is developed using the Fourier–Galerkin (FG) method and compared to the results of an advanced finite element (FE) model. An excellent agreement is observed between the FG and FE solutions for different Reynolds numbers which demonstrates the viability of the solutions in benchmarking buoyancy-driven flow numerical codes.

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.

Uncontrolled subsurface evaporite dissolution could lead to hazards such as land subsidence. Observed subsidences in a study area of Northwestern Switzerland were mainly due to subsurface dissolution (subrosion) of evaporites such as halite and gypsum. A set of 2D density driven flow simulations were evaluated along 1000 m long and 150 m deep 2D cross sections within the study area that is characterized by tectonic horst and graben structures. The simulations were conducted to study the effect of the different subsurface parameters that could affect the dissolution process. The heterogeneity of normal faults and its impact on the dissolution of evaporites is studied by considering several permeable faults that include non-permeable areas. The mixed finite element method (MFE) is used to solve the flow equation, coupled with the multipoint flux approximation (MPFA) and the discontinuous Galerkin method (DG) to solve the diffusion and the advection parts of the transport equation. Results show that the number of faults above the lower aquifer that contains the salt layer is considered as the most important factor that affects the dissolution compared to the other investigated parameters of thickness of the zone above the halite formation, a dynamic conductivity of the lower aquifer, and varying boundary conditions in the upper aquifer.

Fine sediment decreasing gravel permeability and oxygen supply to incubating salmonid embryos, is often considered the main contributing factor for the observed decline of salmonid populations. However, oxygen supply to salmonid embryos also depends on hydraulic conditions driving water flow through the redd. A more generalized perspective is needed to better understand the constraints on successful salmonid incubation in the many heavily modified fluvial ecosystems of the Northern Hemisphere. The effects of hydraulic gradients, riverbed and redd morphology as well as fine sediment deposition on dissolved oxygen (DO) and water exchange was studied in 18 artificial redds at three sites along a modified river. Fifty percent of the redds in the two downstream sites were lost during high flow events, while redd loss at the upstream site was substantially lower (8%). This pattern was likely related to increasing flood heights from up- to downstream. Specific water infiltration rates (q) and DO were highly dynamic and driven on multiple temporal and spatial scales. Temporally, the high permeability of the redd gravel and the typical pit-tail structure of the new built redds, leading to high DO, disappeared within a month, when fine sediment had infiltrated and the redd structure was leveled. On the scale of hours to days, DO concentrations and q increased during high flows, but decreased during the falling limb of the water level, most likely related to exfiltration of oxygen depleted groundwater or hyporheic water. DO concentrations also decreased under prolonged base flow conditions, when increased infiltration of silt and clay particles clogged the riverbed and reduced q. Spatially, artificial log steps affected fine sediment infiltration, q and interstitial DO in the redds. The results demonstrate that multiple factors have to be considered for successful river management in salmonid streams, including riverbed structure and local and regional hydrogeological conditions.

Extensive land subsidence can occur due to subsurface dissolution of evaporites such as halite and gypsum. This paper explores techniques to simulate the salt dissolution forming an intrastratal karst, which is embedded in a sequence of carbonates, marls, anhydrite and gypsum. A numerical model is developed to simulate laminar flow in a subhorizontal void, which corresponds to an opening intrastratal karst. The numerical model is based on the laminar steady-state Stokes flow equation, and the advection dispersion transport equation coupled with the dissolution equation. The flow equation is solved using the nonconforming Crouzeix–Raviart (CR) finite element approximation for the Stokes equation. For the transport equation, a combination between discontinuous Galerkin method and multipoint flux approximation method is proposed. The numerical effect of the dissolution is considered by using a dynamic mesh variation that increases the size of the mesh based on the amount of dissolved salt. The numerical method is applied to a 2-D geological cross section representing a Horst and Graben structure in the Tabular Jura of northwestern Switzerland. The model simulates salt dissolution within the geological section and predicts the amount of vertical dissolution as an indicator of potential subsidence that could occur. Simulation results showed that the highest dissolution amount is observed near the normal fault zones, and, therefore, the highest subsidence rates are expected above normal fault zones.

Understanding the factors that determine successful salmonid embryo incubation in the many structurally modified river systems of the Northern Hemisphere is crucial for maintaining healthy salmonid populations. In this context, the joint impact of fine sediment accumulation together with anthropogenic river modifications on salmonid embryo survival has been rarely investigated. We investigated brown trout embryo survival to hatch (STH) together with ten physicochemical, hydraulic and morphological parameters in artificial brown trout redds in a heavily modified stream (i.e. channelized, artificial log steps) in central Switzerland. We were interested to understand whether (i) STH is more sensitive to the timing and duration of low oxygen rather than a mean oxygen concentration, (ii) STH was negatively affected by increased fine sediment deposition decreasing redd gravel permeability, (iii) higher water levels, causing fine sediment resuspension, benefit STH, (iv) STH was negatively affected by organic content in the redds and especially (v) hydraulic gradients related to redd scale bed-form and/or the artificial step structure benefit embryo STH, and hence could mitigate the negative impact of fine sediment and/or organic content. Up to 50%, brown trout embryos survived with interstitial oxygen exceeding 3 mg L−1. Embryos endured up to 6 days ≤ 1 mg L−1 but were more sensitive to oxygen depletion close to hatch. Therefore, timing and duration of low oxygen were important for embryo STH, and hence, oxygen dynamics need to be considered when assessing in redd conditions for salmonid STH. Partial least squares regression identified the horizontal hydraulic gradient, Fredle index, distance to artificial log steps upstream and amount of accumulated fine sediment as influential predictors for embryo STH. The water level above the redd and total organic carbon content in the redd were not influential. Among the identified influential predictors, 70.9% of the variation in STH could be explained by a logistic regression model containing redd distance to the next upstream step (26.4%, P = 0.004), Fredle index (27.2%,P = 0.003) and horizontal hydraulic gradient (10.1%, P = 0.04). In the logistic regression, the amount of accumulated fine sediment (P = 0.75), field seasons (P = 0.93) and field sites (P = 0.66) was non-significant. In summary, brown trout STH was sensitive to redd gravel permeability, which was measured as Fredle index and affected by fine sediment deposition. At the same time, hydraulic gradients related to artificial log steps, which enhanced hyporheic exchange, benefited embryo STH, and hence mitigated fine sediment impact. This result can be probably transferred to other surface water-dominated river systems with good hyporheic water quality. To what extent it can be transferred to river systems with other hydraulic boundary conditions remains to be evaluated. Altogether, our results clearly indicate that the impact of fine sediment on salmonid incubation success needs to be understood in the hydrological and morphological context of the particular river system.

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.

We have studied the dynamics of water quality in three karst springs taking advantage of new technological developments that enable high-resolution measurements of bacterial load (total cell concentration: TCC) as well as online measurements of abiotic parameters. We developed a novel data analysis approach, using self-organizing maps and non-linear projection methods, to approximate the TCC dynamics using the multivariate data sets of abiotic parameter time-series, thus providing a method that could be implemented in an online water quality management system for water suppliers. The (TCC) data, obtained over several months, provided a good basis to study the microbiological dynamics in detail. Alongside the TCC measurements, online abiotic parameter time-series, including spring discharge, turbidity, spectral absorption coefficient at 254nm (SAC254) and electrical conductivity, were obtained. High-density sampling over an extended period of time, i.e. every 45min for 3months, allowed a detailed analysis of the dynamics in karst spring water quality. Substantial increases in both the TCC and the abiotic parameters followed precipitation events in the catchment area. Differences between the parameter fluctuations were only apparent when analyzed at a high temporal scale. Spring discharge was always the first to react to precipitation events in the catchment area. Lag times between the onset of precipitation and a change in discharge varied between 0.2 and 6.7h, depending on the spring and event. TCC mostly reacted second or approximately concurrent with turbidity and SAC254, whereby the fastest observed reaction in the TCC time series occurred after 2.3h. The methodological approach described here enables a better understanding of bacterial dynamics in karst springs, which can be used to estimate risks and management options to avoid contamination of the drinking water.

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.

River management and restoration measures are of increasing importance for integrated water resources management (IWRM) as well as for ecosystem services. However, often river management mainly considers engineering and construction aspects only and the hydrogeological settings as the properties and functions of ancient fluvial systems are neglected which often do not lead to the desired outcome. Knowledge of the distribution of sediment units could contribute to a more efficient restoration. In this study, we present two noninvasive approaches for delineation of fluvial sediment architecture that can form a basis for the restoration, particularly in areas where site disturbance is not permitted. We investigate the floodplain of a heavily modified low-mountain river in Switzerland using different hydrogeophysical methods. In the first approach, we use data from electromagnetic induction (EMI) with four different integral depths (0.75–6 m) and gamma-spectrometry as well as the elevation data as input for a K-means cluster algorithm. The generated cluster map of the surface combines the main characteristics from multilayered input data and delineates areas of varying soil properties. The resulting map provides an indication of areas with different sedimentary units. In the second approach, we develop a new iterative method for the generation of a geological structure model (GSM) by means of various EMI forward models. We vary the geological input parameters based on the measured data until the predicted EMI maps match the measured EMI values. Subsequently, we use the best matched input data for the GSM generation. The derived GSM provides a 3D delineation of possible ancient stream courses. A comparison with an independent ground penetrating radar (GPR) profile confirmed the delineations on the cluster map as well as the vertical changes of the GSM qualitatively. Thus, each of the approaches had the capacity for detecting sedimentary units with distinct hydraulic properties as an indication of former stream courses. The developed methodology presents a promising tool for the characterization of test sites with no additional subsurface information.