Concepts for the sustainable management of multi-scale flow systems: the groundwater system within the Laufen Basin, Switzerland

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 system

Zeitliche und räumliche Skalen der Fluss-Grundwasser-Interaktion: Ein multidimensionaler hydrogeologischer Untersuchungsansatz

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 Flussbet

Development of monitoring and modelling tools as basis for sustainable thermal management concepts of urban groundwater bodies

Increasing groundwater temperatures observed in many urban areas strongly interfere with the demand of thermal groundwater use. The groundwater temperatures in these urban areas are affected by numerous interacting factors: open and closed-loop geothermal systems for heating and cooling, sealed surfaces, constructions in the subsurface (infrastructure and buildings), artificial groundwater recharge, and interaction with rivers. On the one hand, these increasing groundwater temperatures will negatively affect the potential for its use in the future e.g. for cooling purposes. On the other hand, elevated subsurface temperatures can be considered as an energy source for shallow geothermal heating systems. Integrated thermal management concepts are therefore needed to coordinate the thermal use of groundwater in urban areas. These concepts should be based on knowledge of the driving processes which influence the thermal regime of the aquifer. We are currently investigating the processes influencing the groundwater temperature throughout the urban area of Basel City, Switzerland. This involves a three-dimensional numerical groundwater heat-transport model including geothermal use and interactions with the unsaturated zone such as subsurface constructions reaching into the aquifer. The cantonal groundwater monitoring system is an important part of the data base in our model, which will help to develop sustainable management strategies. However, single temperature measurements in conventional groundwater wells can be biased by vertical thermal convection. Therefore, multilevel observation wells are used in the urban areas of the city to monitor subsurface temperatures reaching from the unsaturated zone to the base of the aquifer. These multilevel wells are distributed in a pilot area in order to monitor the subsurface temperatures in the vicinity of deep buildings and to quantify the influence of the geothermal use of groundwater. Based on time series of the conventional groundwater wells, the multilevel observation wells and the different boundary conditions we characterize the groundwater temperature regimes using a regional groundwater heattransport model. In the urban area of Basel, mean annual groundwater temperatures are significantly increasing with 0.05 K per year in the period of 1994 to 2014, which is most likely due to anthropogenic influences. Overall, mean annual groundwater temperatures of Basel are 3.0 ± 0.7 K higher compared to the mean annual air temperature, which is considered the expectable natural groundwater temperature. Additionally, the findings highlight the importance of appropriate monitoring systems for quantifyin

Prediction of Groundwater Flow and Transport Processes in an Urban Area: A Combined Approach of Field Testing and Numerical Modeling

Drinking water supply in urban areas is challenging due to different kinds of water use and potential groundwater contamination. We investigate an area where drinking water production is close to different contaminated sites. The study site is characterized by a high complexity of the tectonic and geological setting with a gravel and a karstic aquifer. The two aquifers are partly connected, partly disconnected by an aquitard. To avoid drinking water contamination, artificial groundwater recharge with surface water into the gravel aquifer is used to create a hydraulic barrier between the contaminated sites and the water abstraction wells. Trace compounds, that were found in former times in the surface water but not nowadays, are still detected in the extracted drinking water. Different studies have been performed such as numerical modeling, intensive groundwater monitoring and investigation of drilling cores to get a differentiated overview of the distribution of the contaminants. Back-diffusion from the matrix due to changing hydraulic boundary was stated to be the reason for the actual distribution of the contaminants. In a first approach due to the lack of experimental data or evidence from field measurements, the permeabilities of the karstic aquifer were assumed as homogeneous. In our study, we seek to identify the flow and transport processes within the system including the fracture network in a combined approach of field work and 3D modeling with FEFLOW. During a field campaign we acquired water samples for the analysis of stable water isotopes as well as organic and inorganic compounds. Furthermore, tritium and helium samples were taken to estimate water ages and to determine the flow through the fracture networks. A combination of existing and recently obtained data was used to build and validate a 3D flow and transport model. The simulation of different scenarios such as the water flow for varying injection and extraction rates as well as particle transport from different sources is carried out. To investigate the effect of subsurface heterogeneity, PEST, an independent parameter estimation and uncertainty analysis software, was used. With the calibrated model we will be able to optimize the operational conditions of artificial recharge and drinking water production especially at the boundaries of the production field. Hence, we can provide guidelines for an improved water resource management

Governance of shallow geothermal energy resources

Successful electrification of cities' heating and cooling demands depends on the sustainable implementation of highly efficient ground source heat pumps (GSHP). During the last decade, the use of shallow geothermal energy (SGE) resources in urban areas has experienced an unprecedented boost which nowadays is still showing a steady 9% market growth trend. However, the intensive market incorporation experienced by this technology entails different responsibilities towards the long-term technical and environmental sustainability in order to maintain this positive trend. Here we present a SGE management framework structure and a governance model agreed among 13 European Geological Surveys, providing a roadmap for the different levels of management development, adaptable to any urban scale, and independent of the hydrogeological conditions and the grade of development of SGE technology implementation. The management approach reported is based on the adaptive management concept, thus offering a working flow for the non-linear relationship between planning, implementation and control that establishes a cyclical and iterative management process. The generalized structure of the SGE management framework provided allows the effective analysis of policy to identify and plan for management problems and to select the best management objectives, strategies and measures according to the policy principles proposed here

Process-oriented concepts for adaptive water resource management. implications for urban hydrogeology

The present thesis illustrates process-oriented methods for water resource monitoring, management and protection. The methods have been applied and tested for specific questions arising in the context of urban hydrogeology within selected areas in the region of Basel, Switzerland. The results contribute to an integrated perception of surface and subsurface water resources in urban areas. Although the topics of the investigations may differ in terms of objectives and scales, the concept and methods are characteristic for many hydrogeologic problems in urban environments. The basic principles of adaptive groundwater management include the identification of the current profiles of groundwater systems. The methods applied facilitate the evaluation of the sum of impacts and their interaction in time and space with changing hydrological, operational, technical and even geological boundary conditions. The thesis consists of five parts (Parts I-V), including this executive summary, an introduction, a general summary together with the discussion of results and conclusions. Each part represents an already published or submitted scientific article. The investigations address a variety of site-specific questions arising from different scales in the context of urban hydrogeology. All parts deal with impacts of engineering projects and infrastructure development on surface and groundwater systems. Part I illustrates that, with the aid of groundwater modeling, the dynamics of the groundwa­ter ?ow regime under changing spatial and temporal constraints could be simulated and evaluated successfully during the various project phases of a tunnel highway construction. The results allowed to optimize groundwater monitoring, management and protection and to progressively evaluate different engineering proposals. The methods presented in Part II exemplify quantitative data fusion for urban hydrogeology as a practical tool for subsurface characterization. The applied techniques allow integrating different type and quality data into groundwater models and to quantify the effect of groundwater flow budgets and velocities in individual sedimentary structures. Obviously, groundwater flow in heterogeneous media occurs largely through interconnected highly permeable sedimentary structures. In Part III process-oriented approaches for adaptive groundwater management in urban areas is illustrated by selected examples in the region of the city of Basel. The concept focuses on the influence of various water engineering projects on the future development of water resources and associated flow regimes. Further emphasis is on the transient character of river-groundwater interaction and the revision of existing protection concepts. Part IV and V illustrate the results of a project dealing with urban infrastructure maintenance and development at a smaller scale. Subsidence of a river dam and an adjacent highway, both constructed on gypsum-containing rock, required remedial construction measures. This case study presents comprehensive research within a gypsum karst site. Next to universal measurements and monitoring technologies, investigative methods with predictive character are developed that allow long-term predictions on the future evolution of the system and on further subsidence. This part further illustrates that the proposed concept and methods can be used for the setup of monitoring networks and the development of adaptive water management tools on the one hand, but also can be applied for basic research on the development of gypsum karst systems on the other hand. The various investigative methods for karst aquifer characterization complement each other and allow the interpretation of short-term impacts and long-term developments. The scientific achievements of this thesis include: (1) the implementation of a concept for adaptive and integrated water resource management; (2) the demonstration of integrating different methods and tools for process-oriented investigations in urban areas (monitoring, modeling, hydrogeophysics, etc.); (3) the fusion of qualitative and quantitative geological and hydrological information of different quality to describe aquifer heterogeneity; (4) the revision of existing protection concepts and approaches for risk assessment; (5) the application of karst evolution modeling based on genuine field data; (6) novel iterative approaches for the setup and combination of groundwater and karst evolution modeling techniques; (7) methods applied to characterize short-term impacts and long-term development of flow regimes in karst areas and (8) suggestions for monitoring strategies, including the development of tools that can be used for prediction in urban hydrogeology

Thermal management of urban subsurface resources - Delineation of boundary conditions

Shallow subsurface resources are progressively used for the production of geothermal energy, i.e. for the installation and operation of a broad variety of Geothermal Energy Systems (GES). Additionally, in many urban areas there is a surplus of heat from large buildings and constructions reaching into the groundwater saturated zone. Likewise, groundwater is more often used as a cheap cooling medium. As a result, significantly increased subsurface temperatures have been observed in many urban areas. Several studies investigated how the so-called "Subsurface Urban Heat Island" (SUHI) effect and how current thermal subsurface regimes developed. However, a sustainable management of subsurface resources requires a general understanding on how “current thermal states” of subsurface and thermal regimes developed in context of different urban settings and boundary conditions. These aspects yet are mostly unexplored. In practice mitigation measures are generally taken for individual projects. Thereby, a consideration of the broader context of hydrogeological and thermal processes and boundaries and the interacting thermal activities could lead to a more sustainable use of subsurface energy resources. Besides providing an overview of subjects related to the thermal management of urban subsurface resources this review paper summarizes the results from different research projects that have been realized in the densely urbanised area of Basel in northwestern Switzerland