Simultaneous flow of water and air across the land surface during runoff

This paper presents an inter-compartment boundary condition for the simulation of surface runoff, soil moisture, and soil air as a coupled system of partial differential equations. The boundary condition is based on a classic leakance approach to balance water between differently mobile regions such as the land surface and subsurface. Present work applies leakances to transfer water and air simultaneously through the land surface for soils, which are connected by an air flux with a steady atmosphere. Shallow flow and two phase flow in a porous medium are sequential calculated in an iteration loop. General criteria are stated to guarantee numerical stability in the coupling loop and for leakances to control inter-compartment fluid fluxes. Using the leakance approach, a numerical model captures typical feedbacks between surface runoff and soil air in near-stream areas. Specifically, displacement of water and air in soils is hampered at full-water saturation over the land surface resulting in enhanced surface runoff in the test cases. Leakance parameters permit the simulation of air out-breaks with reference to air pressures, which fluctuate in the shallow subsurface between two thresholds

Evaluating Remediation Potential Of A Salinized Heterogeneous Aquifer System Using Three-Dimensional, Density-Dependent Groundwater Modeling

In arid regions, groundwater is the most reliable source for freshwater. Thus, ensuring an aquifer’s long-term stability is one of the fundamental tasks for nowadays groundwater management. Especially in agriculturally used coastal regions, where water consumption exceeds annual recharge, water table drawdown and subsequent saline intrusion are problems that need to be addressed. Wihin the context of the government-funded research project „International Water ResearchAlliance Saxony“, groundwater quality for near-coastal, agriculturally used areas was investigated under the influence of marine saltwater intrusion. In the study region’s near-coastal areas, agricultural development increased tremendously during recent decades, while a steady lowering of the groundwater level was observed, which is primarily due to uncontrolled groundwater mining. Extracted water is mainly used for local irrigation. Intensively decreased groundwater levels, cause an inversion of the hydraulic gradient leading to intrusion of marine saltwater, endangering the productivity of farms. Utilizing the modeling software package OpenGeoSys, which is developed and enhanced by the Department of Environmental Informatics at UFZ Leipzig (Kolditz et al., 2012), a three-dimensional, density-dependent model including groundwater flow and mass transport was built up (Walther, et al., 2012a). The model comprises a heterogeneous hydro-geology (Walther et al., 2012b). A pre-development steady-state was calibrated successfully offering initial conditions for an adjacent transient calibration yielding acceptable results within apparent uncertainties of input parameters. The numerical model was used to investigate a best-case scenario assessing remediation potential of the salinized aquifer. The scenario considers ceasing groundwater abstraction and evaluates time scale and spatial distribution along the coast of the saltwater retreat. Using advanced visualization techniques in a virtual reality (Walther et al., 2013), results show a heterogeneous distribution of the saltwater withdrawal. Remediation actions will require a long-term strategy to retreive the already salinized regions of the aquifer. Results reveal valuable insight for future measurement campaings and management

Ein Euler-Lagrange'sches Konzept für Transportprozesse in gekoppelten Hydrosystemen

Das Verstehen und die Prognose von Wasserqualität bedingen eine gleichzeitige Kenntnis von Wasserherkunft und Fließwegen, da die Hydrology von Strömen und Einzugsgebieten eng miteinander verknüpft sind. Die Überbrückung verschiedenartiger Zeit- und Raumskalen ist eine der Hauptherausforderungen bei der numerischen Untersuchung des Wasserkreislaufes der Erde. Ein physikalisch basiertes numerisches Model zur Kopplung von Oberflächen- und Grundwasser einschließlich des Stoff- und Wärmetransportes wurde innerhalb des Programmpaketes OpenGeoSys entwickelt. Die hydrologischen Prozesse Oberflächen-, gesättigte und ungesättigte Strömung werden durch Diffusionsgleichungen beschrieben und mit Finite-Elemente und Finite-Volumen Verfahren gelöst. Neu ist die Anwendung von Lagrangeschen stochastischen Partikeln (random walk particle tracking) zur Simulation von advektiv-diffusivem/dispersivem Transport in gekoppelten Hydrosystemen. Alternativ können auch Eulersche Methoden verwendet werden. Das Kopplungskonzept ist ein Kompartiment-Ansatz. Typischerweise wird die Hydrosphäre in Oberflächen-, Boden- und Aquifer-Kompartimente aufgeteilt, welche über Austauschflüsse an gemeinsamen Schnittstellen interagieren. Jeder Prozess wird mit seiner eigenen räumlichen und zeitlichen Diskretisierung gelöst und eine weitere Kopplungsschleife wird ausgeführt (partitionierte Kopplung). Ein Schlüssel zur objektorientierten Implementierung des Kompartiment-Ansatzes ist eine Hierarchie von geometrischen, topologischen (Diskretisierungsnetzen) und Prozessbibliotheken, welche für Multiphysik-Probleme entworfen wurden. Die objektorientierte Umgebung von OpenGeoSys für Hochleistungsrechnen wurde bei der Entwicklung eines regionalen hydraulischen Bodenmodelles genutzt. Ein zentraler Teil dieser Arbeit ist die Untersuchung des neuen Modelles mit einigen Anwendungsbeispielen, welche hydrologische und Transportprozesse von Labor- bis Einzugsgebietsskala umspannen: Zwei Benchmark-Tests zu Horton'schem und Dunn'schem Oberflächenabfluss, eine Modellierungsstudie zu Cryptosporidium parvum Oozysten und drei Fallstudien - am Flussbecken der Lahn in Deutschland, dem Untersuchungsgebiet Borden in Kanada und dem Beerze-Reusel Einzugsgebiet in den Niederlanden.Understanding and predicting water quality require the concomitant knowledge of water origin and flow paths as stream and catchment hydrology are intimately linked. Bridging of various temporal and spatial scales is a key challenge in the numerical investigation of the terrestrial hydrologic cycle. A physically based numerical model for coupled surface and subsurface water flow with heat and mass transport has been developed in the software toolbox OpenGeoSys. The hydrological processes surface water flow, unsaturated, and saturated flow are described by diffusion type equations and solved with finite element and finite volume methods. New is the application of Lagrangian stochastic particles (random walk particle tracking) for the simulation of advective-diffusive/dispersive transport in coupled hydrosystems. Alternatively, Euler methods can be used. The coupling concept is a compartment approach. Typically, the hydrosphere is subdivided in surface, soil, and aquifer compartments, which interact via exchange fluxes at common interfaces. Each process is numerically solved with its own spatial and temporal discretization and an additional coupling loop is executed (partitioned coupling). A key to the object-oriented implementation of the compartment approach is a hierarchy of geometric, topologic (discretization meshes), and process libraries designed for multiphysics problems. The object-oriented environment of OpenGeoSys for high performance computing was used in the development of a regional hydraulic soil model. A central part of this work is the examination of the novel model with several application examples spanning hydrological and transport processes from laboratory to catchment scales: Two benchmark tests on Horton and Dunne overland flow, a modeling study on Cryptosporidium parvum oocysts, and three case studies - at the Lahn river basin in Germany, the Borden site in Canada, and the Beerze-Reusel drainage basin in the Netherlands

The OGS-Eclipse code for simulation of coupled multiphase flow and geomechanical processes in the subsurface

This paper presents a numerical simulation tool for the analysis of coupled processes related to subsurface operations. The tool combines the open-source scientific code OpenGeoSys with the reservoir simulator Eclipse enabling the coupling of thermal, hydraulic, mechanical and geochemical processes. While the coupling of multiphase flow with heat and reactive geochemical component transport has been already implemented, OpenGeoSys-Eclipse is now extended for the coupling of multiphase flow and deformation. By this, OpenGeoSys-Eclipse is capable of addressing the impact of pore pressure changes on rock stability and deformation as well as the feedback effects of geomechanical processes on multiphase flow via pore volume coupling and porosity and permeability update. The coupling is verified by several test cases of gas storage scenarios and compared with reference simulations of OpenGeoSys. The results are in good agreement regarding the general effects of geomechanical feedback on pore pressure as well as porosity and permeability changes. Differences in the results are only observed for the pore volume coupling arising from the different implementation of rock compressibility models in the two simulators. The simulations are furthermore used to investigate the relevance of addressing geomechanical feedback in numerical scenario simulations for the assessment of subsurface operations. The results show clearly, that, depending on the given storage site conditions and rock types, the feedback of deformation on pore pressure can be significant and should therefore be accounted for in the assessment

The OGS-Eclipse code for simulation of coupled multiphase flow and geomechanical processes in the subsurface

<jats:title>Abstract</jats:title><jats:p>This paper presents a numerical simulation tool for the analysis of coupled processes related to subsurface operations. The tool combines the open-source scientific code OpenGeoSys with the reservoir simulator Eclipse enabling the coupling of thermal, hydraulic, mechanical and geochemical processes. While the coupling of multiphase flow with heat and reactive geochemical component transport has been already implemented, OpenGeoSys-Eclipse is now extended for the coupling of multiphase flow and deformation. By this, OpenGeoSys-Eclipse is capable of addressing the impact of pore pressure changes on rock stability and deformation as well as the feedback effects of geomechanical processes on multiphase flow via pore volume coupling and porosity and permeability update. The coupling is verified by several test cases of gas storage scenarios and compared with reference simulations of OpenGeoSys. The results are in good agreement regarding the general effects of geomechanical feedback on pore pressure as well as porosity and permeability changes. Differences in the results are only observed for the pore volume coupling arising from the different implementation of rock compressibility models in the two simulators. The simulations are furthermore used to investigate the relevance of addressing geomechanical feedback in numerical scenario simulations for the assessment of subsurface operations. The results show clearly, that, depending on the given storage site conditions and rock types, the feedback of deformation on pore pressure can be significant and should therefore be accounted for in the assessment.</jats:p&gt