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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

Detailed measurements of physical, chemical and biological dynamics in groundwater are key to understanding the important processes in place and their influence on water quality – particularly when used for drinking water. Measuring temporal bacterial dynamics at high frequency is challenging due to the limitations in automation of sampling and detection of the conventional, cultivation-based microbial methods. In this study, fully automated online flow cytometry was applied in a groundwater system for the first time in order to monitor microbial dynamics in a groundwater extraction well. Measurements of bacterial concentrations every 15 minutes during 14 days revealed both aperiodic and periodic dynamics that could not be detected previously, resulting in total cell concentration (TCC) fluctuations between 120 and 280 cells μL−1. The aperiodic dynamic was linked to river water contamination following precipitation events, while the (diurnal) periodic dynamic was attributed to changes in hydrological conditions as a consequence of intermittent groundwater extraction. Based on the high number of measurements, the two patterns could be disentangled and quantified separately. This study i) increases the understanding of system performance, ii) helps to optimize monitoring strategies, and iii) opens the possibility for more sophisticated (quantitative) microbial risk assessment of drinking water treatment systems., Scientific Reports, 6, ISSN:2045-2322

The high volume of water inflow into tunnel plays a significant role in the design of drainage systems and exerts bio-environmental effects. In engineering practice, analytical and empirical methods that are commonly used to estimate water inflow in sedimentary rock masses, lack sufficient accuracy. The geostructural anisotropy in a fractured rock has a great impact on water inflow. In discontinuous media, anisotropy and heterogeneity of the fractured rock masses are highlited. Hence, these methods are not efficient to calculate water inflow to tunnel in such media, due to the assumed isotropic hydraulic coefficient. In this regard, an empirical formula is developed in this study for hydraulic conductivity in the fractured rock masses for analytical methods, alternately used to predict water inflow. To achieve this, a discrete network flow model was performed. The simulation resulted in a dataset that is helpful in developing hydraulic conductivity empirical formula for well-known Goodman equation. The geostructural parameters, such as the joint orientation, aperture, spacing and joint interconnectivity were included to determine this formula. The acquired empirical equation was utilized in the evaluation of groundwater inflow to middle-depth Amirkabir tunnel in north of Iran. In comparison to the observerd flow, analytical methods resulted in higher overestimation, especially in the sites with high anisotropy. However, empirical model led to a better estimation of water inflow to tunnel.

The impact, caused by a construction of a dam site on the Birs river close to Basel (Switzerland), on the evolution of a gypsum-karst aquifer in the vicinity of the hydraulic building, is studied. Several sinkholes provoked subsidence of the dam and the highway nearby. Extensive technical measures had to be conducted in order to prevent further karstification. The numerous geophysical and geological field studies executed in the area, together with a 3D hydrogeological model of the aquifer, provide a very detailed information about the boundary conditions, and the local properties determining the karstification. In this work, we present a 2D karst evolution model of the aquifer in the vicinity of the dam structure. In contrast to older studies, this time the focus of the research is not the basic processes governing the karst evolution, but modeling the temporal development of the real aquifer. Using the large amount of information about the location, we demonstrate that a detailed knowledge of the local properties of the rock (hydraulic conductivity, solubility) is of crucial importance when modeling real aquifers. From a wide range of possible evolution scenarios, we deduce a warning that solutional features, such as sinkholes, can develop far away from the hydraulic structure and endanger facilities at the surface. Our model is able to reproduce and successfully explain the main geological features revealed by field studies. We suggest a workflow to combine the data from field observations, groundwater modeling, and karst evolution modeling and to study the karstification of real aquifers. We propose a scenario for the evolution of the aquifer and a reasonable range for the values of the basic parameters governing the karstification.

We present a three-dimensional model describing the evolution of a gypsum karst aquifer along the Birs river near Basel in Switzerland. Here, a small dam-site was built in 1890 to generate hydro-electric power. After subsidence of a nearby highway, geophysical and geological field studies have been carried out and a detailed hydrogeological model has been developed. These observations identified a karstified weathered zone as the reason for the subsidence. To prevent any further damage, remedial construction measures have been carried out. We employ our numerical model KARSTAQUIFER, which simulates the temporal evolution of a karst system by dissolution, increasing the porosity in the aquifer. We used results from geological and geophysical investigations as a priori information for implementing the initial boundary conditions into our three-dimensional numerical model. Our model accounts for topography, precipitation and geology and especially for the anisotropy of the local bedrock. It can successfully reproduce the weathered zone in its current horizontal and vertical extent. We cm also simulate the possible evolution of the aquifer following a remedial construction phase. Therefore, taken together with the geophysical and geological observations and the groundwater model, our three-dimensional karst aquifer evolution model enhances the understanding of the development of this heterogeneous karst aquifer system. (C) 2012 Elsevier B.V. All rights reserved. Hydrogeologie der Nordwestschweiz, Grundwasser

Summary Although alluvial aquifers connected to rivers can be a rich source of drinking water, they are susceptible to contamination by infiltrating river water. The processes governing river–groundwater interaction are variable in time and space. Natural filtration mechanisms are often not sufficient during high discharge events in the river. To capture the dynamics of river–groundwater interaction, indicator parameters that can serve as proxies for river water infiltration need to be derived. Principal component analysis of continuously measured time series was used to identify indicator wells and derive indicator parameters for a study area in NW Switzerland. The results showed different sources of variation in the parameters, including river stage fluctuations. The multivariate approach highlighted differences between observation wells based on the response of the measured parameters to effects of damping and delay of the input signals. Three observation wells were shown to be representative of river–groundwater interaction dynamics in the study area. Of the three parameters analysed, groundwater head and electrical conductivity are recommended as a combined proxy for river water infiltration in the study area. In contrast, temperature proved not to be a reliable indicator.

Hydrogeology Journal, 19 (7), ISSN:1431-2174, ISSN:1435-0157

Modelling variable density flow problems under heterogeneous porous media conditions requires very long computation time and high performance equipments. In this work, the DASPK solver for temporal resolution is combined with advanced spatial discretization schemes in order to improve the computational efficiency while maintaining accuracy. The spatial discretization is based on a combination of Mixed Finite Element (MFE), Discontinuous Galerkin (DG) and Multi-point Flux Approximation methods (MPFA). The obtained non-linear ODE/DAE system is solved with the Method of Lines (MOL) using the DASPK time solver. DASPK uses the preconditioned Krylov iterative method to solve linear systems arising at each time step. Precise laboratory-scale 2D experiments were conducted in a heterogeneously packed porous medium flow tank and the measured concentration contour lines are used to evaluate the numerical model. Simulations show the high efficiency and accuracy of the code and the sensitivity analysis confirms the density dependence of dispersion.

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.

Rapid changes in spring water quality in karst areas due to rapid recharge of bacterially contaminated water are a major concern for drinking water suppliers and users. The main objective of this study was to use field experiments with fecal indicators to verify the vulnerability of a karst spring to pathogens, as determined by using a numerical modeling approach. The groundwater modeling was based on linear storage models that can be used to simulate karst water flow. The vulnerability of the karst groundwater is estimated using such models to calculate criteria that influence the likelihood of spring water being affected by microbial contamination. Specifically, the temporal variation in the vulnerability, depending on rainfall events and overall recharge conditions, can be assessed and quantified using the dynamic vulnerability index (DVI). DVI corresponds to the ratio of conduit to diffuse flow contributions to spring discharge. To evaluate model performance with respect to predicted vulnerability, samples from a spring were analyzed for Escherichia coli, enterococci, Clostridium perfringens, and heterotrophic plate count bacteria during and after several rainfall events. DVI was shown to be an indication of the risk of fecal contamination of spring water with sufficient accuracy to be used in drinking water management. We conclude that numerical models are a useful tool for evaluating the vulnerability of karst systems to pathogens under varying recharge conditions.

Zusammenfassung: Die Zahl an Erdwärmesonden nimmt in ganz Europa stetig zu. Wie mit anderen Technologien der Energiegewinnung sind auch mit Erdwärmesonden Risiken verbunden. Deshalb bedarf es Leitlinien als Grundlage für die Bewilligungsverfahren, die den Bau und Betrieb einer solchen Anlage regeln. Um dabei den zu erwartenden Nutzen gegen mögliche Risiken abwägen zu können, sind Kenntnisse über die hydrogeologischen Verhältnisse am Standort und die dort stattfindenden Prozesse erforderlich. Am Beispiel des Erdwärmenutzungskonzepts des Kantons Basel-Landschaft wird gezeigt, wie die Bewilligung von Erdwärmesonden differenziert geregelt werden kann, und wie die geologischen Merkmale einer Region in ein Erdwärmenutzungskonzept integriert werden können. Dabei werden insbesondere Karstgebiete, Gebiete mit der Gefahr des Gebirgsquellens und der Subrosion, Gewässerschutzbereiche, und Gebiete mit Grundwasserstockwerkbau oder gespannten Grundwasserverhältnissen berücksichtigt. Der Artikel will damit einen Beitrag zur derzeit stattfindenden gesellschaftlichen Diskussion über den Nutzen und die Risiken der untiefen Geothermie leisten, indem er Risiken durch den Bau und Betrieb von Erdwärmesonden beschreibt, und Möglichkeiten aufzeigt, diese Risiken in der Bewilligungspraxis zu berücksichtigen

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.

To understand how groundwater resources may be affected by climate change and create sustainable management plans, modeling karst systems provides much insight.

Transmissive and reflective intensity measurements for visual concentration determinations in 2D flow tank experiments were compared and evaluated for their applicability in the study of flow and transport phenomena. A density-dependent heterogeneous flow experiment was conducted and transmission and reflection images of the dyed saltwater plume were analyzed. A single light source and dark curtains forced the light to pass through the porous media only, thus facilitating the transmission measurements. The reflection images delivered a more homogeneous spatial illumination than the transmission images. Major perturbations of the transmission images were lens flare effects and light dispersion within the bead-water-Plexiglas system which smear the front of the plume. Based on the conducted evaluation of transmissive and reflective intensity measurements, the reflection data delivered more reliable intensity values to derive solute concentrations in intermediate scale flow tank experiments.

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.

High-resolution depth-oriented temperature measurements havebeen introduced to investigate a groundwater body in the urban area of Basel. In total, four devices were installed with up to 16 sensors- located in both the saturated and unsaturated zone. Measurements were performed over a period of 4 years and provide sufficient data to set up and calibrate high-resolution numerical local heat-transport models. Calibration was performed for the saturated and unsaturated zone, respectively. Model results show that although depth-oriented measurements provide valuable insights into local thermal processes, the identification of governing and impacting factors strongly depends on appropriate positioning of the measurement device. High-resolution depth-oriented temperature measurements havebeen introduced to investigate a groundwater body in the urban area of Basel. In total, four devices were installed with up to 16 sensors- located in both the saturated and unsaturated zone. Measurements were performed over a period of 4 years and provide sufficient data to set up and calibrate high-resolution numerical local heat-transport models. Calibration was performed for the saturated and unsaturated zone, respectively. Model results show that although depth-oriented measurements provide valuable insights into local thermal processes, the identification of governing and impacting factors strongly depends on appropriate positioning of the measurement device. Hydrogeologie der Nordwestschweiz, Grundwasser in Basel

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.

This article presents a numerical model of a part of an aquifer that is recharged by infiltration from the Swiss pre-Alpine river Toss in the Linsental (north-eastern Switzerland). The nearby city of Winterthur makes use of this aquifer as a resource of drinking water. The presented model is part of a larger interdisciplinary research program undertaken with the goal to evaluate the possible impacts of a planned revitalization of the severely canalized river Toss. Above all it should show the extent of decrease of the groundwater residence time if the river bed is allowed to move towards the drinking water wells. The flow model was constrained and calibrated by transport modelling of tritiogenic 3 He. This tracer reflects both the aging of the water (by accumulation of 3 He resulting from tritium-decay) as well as the two different components of the mixture (river water free of tritiogenic 3 He due to degassing, and groundwater enriched in 3 He due to accumulation). By simulating a Dirac- pulse-shaped input of a conservative tracer at different sources (river cells or upstream flux boundary cells) it is possible to determine the age distributions as well as the mixing ratios of the two types of water at the two pumping stations within the model area. The same calculations for a hypothetical river course passing directly beside the pumping stations indicate a decrease of the mean residence time of the pumped water together with an increase of the amount of the younger river water component. q 2001 Elsevier Science B.V. All rights reserved.

The investigation of contaminated sites is usually a long and expensive process. It is therefore desirable to use a combination of methodologies in an integrative approach that can reduce redundant information gathering. The objective of this study was to examine the usefulness of 2 non-intrusive exploration techniques in a contaminated site investigation. Borehole positioning based on geophysical measurements was compared to positioning based on the Bayesian expert system for flow-field modeling. The goal set at the field site was the assessment of the type and load of contaminants transported from the landfill site to the adjacent aquifer and the extent of leachate plumes within the groundwater. The two methods made different demands on information gathering and were found to be complementary. The geophysical approach focused attention on the waste compartments at the site and on mixing plumes in the adjacent aquifer but could not, without prior information, provided information on the flow field. The Bayesian approach to flow-field modeling determined areas of greatest model uncertainty at the model boundaries. The model highlighted areas of greatest uncertainty that might otherwise have been overlooked and provided information on the most likely mean direction of the leachate plumes. It was concluded that both methods contribute to a site investigation and should be used before additional drilling is carried out.

Progress towards a better understanding of groundwater circulation and transport processes in aquifers demands a multidisciplinary approach to a host of unresolved problems. Although much progress has been made within recent years in interpreting the dynamic character of groundwater systems, many key issues remain to be addressed. In particular, several areas demand attention: the role of sedimentological information (heterogeneity) in groundwater and transport models, the scaling-up of observations from outcrop scale to larger scales and the integration of geological and geophysical information of different quality into the description of an aquifer structure. Still nowadays many of the heterogeneities cannot be recognized directly because of the limitation of measurement techniques. This is probably one of the reasons for the limited application of aquifer-sedimentology and geophysics in practical cases. In order to consolidate, expand, and make a larger number of people aware of the contribution of modern aquifer-sedimentology, including modelling and ultra-high resolution geophysical methods, several lines of intervention were identified: (1) a better collaboration of the different disciplines on site-specific applied problems; (2) development of new modelling techniques combining data of different quality; (3) development of optimizing tools (position and number of wells, additional geophysical methods, baysian techniques); (4) development of a `common language' among sedimentologists and hydrogeologists to overcome communication problems.

The threat of pollution in the shallow subsurface has led to an increasing need to understand how complex heterogeneities in gravel aquifers influence groundwater transport. To characterize these heterogeneities, we have conducted extensive two-dimensional (2-D) and three-dimensional (3-D) ground-penetrating radar (GPR or georadar) surveys in two quarries within the Rhine valley of northeastern Switzerland. The quarries comprised gravel and sand deposited in a proglacial braided river system that followed the maximum Wurm-stage glaciation. After the surveys, the terrace walls beneath the two study sites were photographed as they were being excavated. By combining information extracted from the 2- and 3-D georadar images with the outcrop photographs, it was possible to correlate georadar facies with the various glaciofluvial architectural elements. The dominant elements were scour pools formed at or near the confluences of two stream channels and horizontally bedded and massive gravel sheets deposited during moderate to high water flow conditions and exposed during low flow conditions. Architectural elements were generally elongated parallel to the mean flow directions of the ancient river system. Variations in the strike of their long axes reflected lateral and vertical changes in the local flow direction. Time slices showed structural trends not evident on 2-D georadar images and photographs. Data interpretation was quicker, more complete and less ambiguous when georadar facies analyses were based on a combination of georadar vertical profiles and time slices than when based on georadar vertical profiles alone.

In this study a three-dimensional stochastic facies-based aquifer model was developed. The model can be used to numerically simulate flow and solute transport in heterogeneous groundwater aquifers. The stochastic generation process can be conditioned by using available facies information in one vertical plane or two orthogonal vertical ones. In this study the information was obtained from a facies interpretation of a vertical georadar profile in a natural gravel formation in Switzerland. In the domain outside the known profile, unconditioned lenses and layers were generated at random according to statistical information on coherent sedimentary structures based on observations in adjacent gravel pits [Jussel et al., 1994a]. The method was applied to a single extraction well designed to capture an initially block-shaped contaminant plume. A total of 80 conditioned and unconditioned synthetic aquifers was generated. The flow and transport simulations were performed using a finite element flow model and a random walk transport model. The results are presented as the ensemble of integral solute mass recovery curves of single realizations. One would expect conditioning to reduce the bandwidth of the recovery curves representing the uncertainty, but the results show that the bandwidth even increased. This effect was attributed to a discrepancy in the mean volumetric fraction of the different facies types in the conditioned and the unconditioned cases. Moreover, a simulation using a homogeneous model with constant equivalent flow and transport parameters overestimated the remediation efficiency. The influence of a linear, reversible equilibrium sorption on the remediation well efficiency was taken into account by an uncorrelated random field of the retardation factor based on values from the literature. However, the impact of the variability in hydraulic conductivity clearly exceeded the effect of the variability in the retardation factor.

Ground penetrating radar (GPR) was used to investigate the structure of the sediments in a floodprone gravel-bed river. Measurements were made on 2 gravel bars and in the adjacent channel. We buried a metallic object to calibrate depth and to visualize changes in GPR-profiles taken before and after digging. In addition, along 2 GPR-profiles the structure of the alluvial sediment of a gravel bar was visually verified by digging a trench down to the groundwater table. The GPR method enables one to distinguish sedimentary units of different texture with a vertical resolution of about 0.25 m. The investigation showed the depth of the alluvial valley fill, and it revealed geomorphological features such as lateral point bar accretion, fills of former pools, or open framework textures. These structures form a complex 3-dimensional mosaic of sediment patches. The GPR method also allowed us to document the changes resulting from bed-moving floods, such as in the formation of homogeneous gravel sheets during high m...

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

This study presents a management concept for the sustainable thermal use of an urban groundwater body. The concept is designed to be applied for shallow thermal groundwater use and is based on (1) a characterization of the present thermal state of the investigated urban groundwater body; (2) the definition of development goals for specific aquifer regions, including future aquifer use and urbanization; and (3) an evaluation of the thermal use potential for these regions. The investigations conducted in the city of Basel (Switzerland) focus on thermal processes down-gradient of thermal groundwater use, effects of heated buildings in the aquifer 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 quantifying the thermal influence on the investigated urban groundwater body, including the influences of thermal groundwater use and additional heat from urbanization. Subsequently, management strategies for minimizing further groundwater temperature increase, targeting "potential natural" groundwater temperatures for specific aquifer regions and exploiting the thermal use potential are discussed.

[1] The Henry semianalytical solution for salt water intrusion is widely used for benchmarking density dependent flow codes. The method consists of replacing the stream function and the concentration by a double set of Fourier series. These series are truncated at a given order and the remaining coefficients are calculated by solving a highly nonlinear system of algebraic equations. The solution of this system is often subject to substantial numerical difficulties. Previous works succeeded to provide semianalytical solutions only for saltwater intrusion problems with unrealistic large amount of dispersion. In this work, different truncations for the Fourier series are tested and the Levenberg-Marquardt algorithm, which has a quadratic rate of convergence, is applied to calculate their coefficients. The obtained results provide semianalytical solutions for the Henry problem in the case of reduced dispersion coefficients and for two freshwater recharge values: the initial value suggested by Henry (1964) and the reduced one suggested by Simpson and Clement (2004). The developed semianalytical solutions are compared against numerical results obtained by using the method of lines and advanced spatial discretization schemes. The obtained semianalytical solutions improve considerably the worthiness of the Henry problem and therefore, they are more suitable for testing density dependent flow codes.

This article presents hydrogeophysical investigations performed in a well-developed, long-term hydrogeological gypsum karst research site where subsurface evaporite dissolution has led to the subsidence of a river dam and an adjacent highway; both constructed on gypsum-containing rock, southeast of Basel, Switzerland. An observation system was set up to improve the protection of surface and subsurface water resources during remedial construction measures of the highway and in order to understand the processes, as well as the temporal evolution, of rock water interaction (flow and dissolution).However, no detailed hydrogeological information beneath the river could be derived from the previous investigations. To supplement the basic knowledge on this area, underwater Electrical Resistivity Tomography (ERT) measurements were conducted in the river bed upstream of the dam. The ERT-data are interpreted together with drill-core information and a conceptual 3D-Model of the area behind the dam and beneath the river. Results help to delineate weathered zones, associated faults and the thickness of sediment deposits behind the dam, as well as to locate voids within the local karst system. The combination of the ERT and modeling allows the optimization of future site-specific remedial construction measures.

Pleistocene gravely braided-river deposits in river valleys constitute a large fraction of the natural ground-water reservoirs in Switzerland. The knowledge of the distribution and variability of hydraulic conductivity within these deposits are key factors for the estimation of water residence times and of description of large-scale mixing procesess in aquifers such as macrodispersion. It has been shown elsewhere that the spatial variability of hydraulic conductivity is related to the composition and the characteristic dimensions of sedimentary structures, which are themselves related to the dynamics of ancient braided-river systems. In many contamination problems, sedimentological information is sparse and drill-core descriptions and pumping-tests only give a limited picture of the geometry of inhomogeneities. The ground-probing radar (GPR) method is a promising tool for resolving changes of physical properties in gravel deposits at the scale of natural inhomogeneities arising from changing sedimentary composition. However, the main limitation of GPR is the rapid attenuation of electromagnetic waves in subsurface sediments such as gravels, which leads to a limited penetration of the order of 10 to 15 m for a 250 MHz antenna. The objectives of our present work are: 1. (1) To show how digital processing methods similar to reflection seismics may be applied for velocity and profile processing. These methods can improve both the resolution of radar profiles, in particular at greater depths, and the determination of velocity distributions from CDP experiments. 2. (2) To examine whether and to what extent the characteristic lithofacies of Pleistocene gravel deposits can be recognized as mappable reflection patterns on ground-probing radar (GPR) reflection profiles in order to gain information about the geometry of inhomogeneities. Using modern digital data processing methods, such as band pass, high- or low-cut filtering, deconvolution and velocity analysis, much more significant information can be obtained from the recorded GRP field data-sets. Our results demonstrate that on GPR reflection images the basic fluvial forms such as (1) pool deposits generated at the junction of two channels, and (2) channel deposits may be distiguished. Their shape and characteristic spatial dimensions may be recognized from a series of profiles in different directions. Because the method can detect changes in the water content, the reflection image may be related even to small changes in the degree of saturation of the sediments. Thus reflectors can indicate the changing composition of sediments.

[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 ).

Within this chapter, we present and discuss several hypotheses and some concepts which we consider as important for urban geology. The first section deals with adaptive subsurface and groundwater resource management in urban areas with a focus on the definition of “system and risk profiles.” The second section discusses the importance and role of “flow across boundaries.” The third section describes an approach for the assessment of “vulnerability” of urban groundwater resources and includes a discussion on how to define “quality control systems.” In the last section, we discuss impacts of anthropogenic and climate change to quantitative and qualitative aspects of groundwater resources in the city Basel.

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.

Urban subsurface resources and especially urban groundwater bodies are particularly vulnerable to environmental impacts and their rational management is of major importance. This book reflects the experience of the authors, working in a multidisciplinary team of specialists and scientists on urban geosciences including geology, hydrogeology, hydrogeophysics, river-ecology and on research projects at the Basel University. Beside the academic activities, the Applied and Environmental Geology (AUG) is in charge of the geologial survey of the Cantons of Basel-Stadt and Basel Landschaft. Modern quantitative earth-sciences can contribute significantly in finding solutions concerning the sustainable use or subsurface resources in urban environments. The approaches we present in this book are mainly problem oriented. This includes the cooperation of specialists from several universities and institutions with different background worldwide to find solutions to specific problems related to urban environmental questions. Hydrogeologie der Nordwestschweiz, Grundwasser

The presented examples and case studies illustrate specific applications of adaptive management of water resources in the region of Basel, Northwestern Switzerland. Such concepts together with the setup of tools and process-oriented experiments allow testing hypotheses. The applied methods facilitated us to fill several gaps of knowledge of subsurface processes. The examples focus on questions with practical as well as research. Most topics are relevant for urban areas and the sustainable use of subsurface resources in general.

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.

[1] A series of laboratory-scale two-dimensional porous medium tank experiments was conducted to study stable-layered variable density flow problems using well-defined experimental parameters and boundary conditions. The experiments were carried out both in a rectangular flow tank and in a more complex geometrical setup aimed at studying variable density flow in geometries similar to geological formations of aquifers and aquicludes connected via fault zones. An impermeable layer within the porous medium tank forced the solutes to pass through a vertical channel, representing a geological fault zone, to reach the outlet of the tank. Flow through the porous medium occurred through a single inflow opening and an outflow opening on the opposite edge of the domain. An image analysis technique delivered 2%, 10%, 50%, and 80% salt concentration isolines at distinct times. Breakthrough curves of the dyed saltwater with an initial density of 1063 g/L were available at any location within the tank. The experimental data are presented as benchmark problems to evaluate numerical codes. A numerical model based on mixed finite elements for the fluid flow problem and a combination of discontinuous Galerkin finite element and multipoint flux approximation methods for the transport turned out to be adequate for the simulation of the physical experiments. The high data availability makes the proposed benchmark experiments a valuable tool for assessing the performance of density-coupled flow models.

The response of fluvial systems to tectonic activity and climate change during the Late Pleistocene influenced sedimentary processes and hence the conditions of river terraces formation. The northern Alpine foreland is well adapted for such studies due to the high sediment input and the variety of depositional environments. This study focuses on sediments of a part of the Rhine River in the area of Basel, at the Border between Switzerland, Germany and France. A detailed evolution of the Lower Terrace is inferred from sedimentological, geomorphologic and pedological observations as well as historical documents, and calibrated using different dating methods (optically stimulated luminescence, uranium series disequilibrium, radiocarbon). The Lower Terrace was deposited during two periods (30–15 ka and 13–11 ka), which correlate with two cold climatic phases, representing the Last Glaciation of the Alps and the Younger Dryas. These ages underline that main incision of the Lower Terrace braidplain in the area of Basel is restricted to post Younger Dryas times, as sediments of that age (13–11 ka) are found atop the highest levels. From then on, a flight of cut-terraces were formed with minor re-accumulation due to Holocene flood events. These findings demonstrate that the surface of a terrace does not always represent the age of sediment aggradation, and this should be remembered when using terraces to reconstruct the tectonic history of an area.

Konz, M., Ackerer, P., Younes, A., Huggenberger, P., Zechner, E., 2009a. 2D Stable Layered Laboratory-scale Experiments for Testing Density-coupled Flow Models. Water Resources Research, 45. doi:10.1029/2008WR007118., a series of laboratory-scale 2D tank experiments were conducted and accurately simulated for density driven flow problems on homogeneous porous media. In the present work, we extended the numerical and experimental studies to heterogeneous problems. The heterogeneous porous medium was constructed with a low permeability zone in the centre of the tank and had well-defined parameters and boundary conditions. Concentration distributions were measured in high resolution using a photometric method and an image analysis technique. The numerical model used for the simulations was based on efficient advanced approximations for both spatial and temporal discretizations. The Method Of Lines (MOL) was used to allow higher-order temporal discretization. Three different boundary conditions, corresponding to different localizations of the inflow and the outflow openings at the opposite edges of the tank, were applied to investigate different flow scenarios in the heterogeneous porous medium flow tank. Simulation results of all three density coupled experiments revealed a density-dependent behavior of dispersion. Thus, a reduction of dispersivites was required to obtain a good matching of the experimental data. The high quality of the experiments enabled a detailed testing of numerical variable-density flow codes under heterogeneous conditions. Therefore, the experiments were considered to be reliable benchmark tests.

[1] Since the genesis and shape of natural deep-seated cavities within a salt body are insufficiently understood, the current study tries to shed some light on this topic. To this end, freshwater was pumped slowly through a horizontal borehole in rock salt cores. Owing to fast halite dissolution kinetics, high solubility, and slow inflow rate, halite dissolution took place only in the inflow of the rock salt cylinder. The shape of the created cavities is an approximately symmetrical half cone with a horizontal base facing upward. A conceptual model is presented that is inspired by the experimental results and based on theoretical hydraulic-geochemical considerations, as well as on field observations. It proposes that triangular prism or conically shaped cavities develop within salt under confined conditions, where aggressive water flows upward along a fracture/conduit from an insoluble aquifer into the soluble stratum. Such cavity enlargements may cause land subsidence and structure collapse.