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  • Walther, Marc  (19)
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  • 1
    Language: English
    Description: This tutorial on the application of the open-source software OpenGeoSys (OGS) in computational hydrology is based on a one-week training course at the Helmholtz Centre...
    Keywords: Earth Sciences -- Hydrogeology; Earth Sciences -- Quantitative Geology; Earth Sciences -- Simulation and Modeling
    ISBN: 978-3-319-13334-8
    ISBN: 3319133349
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  • 2
    Language: English
    In: Journal of Hydrology, August 2017, Vol.551, pp.648-659
    Description: Application of numerical models is a common method to assess groundwater resources. The versatility of these models allows consideration of different levels of complexity, but the accuracy of the outcomes hinges upon a proper description of the system behaviour. In seawater intrusion assessment, the implementation of the sea-side boundary condition is of particular importance. We evaluate the influence of the slope of the sea-side boundary on the simulation results of seawater intrusion in a freshwater aquifer by employing a series of slope variations together with a sensitivity analysis by varying additional sensitive parameters (freshwater inflow and longitudinal and transverse dispersivities). Model results reveal a multi-dimensional dependence of the investigated variables with an increasing relevance of the sea-side boundary slope for seawater intrusion (decrease of up to 32%), submarine groundwater discharge zone (reduction of up to 55%), and turnover times (increase of up to 730%) with increasing freshwater inflow or dispersivity values.
    Keywords: Saltwater Intrusion ; Coastal Aquifers ; Numerical Investigation ; Sea-Side Boundary Condition ; Submarine Groundwater Discharge ; Residence Times ; Opengeosys ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 3
    Language: English
    In: Journal of Contaminant Hydrology, 2014, Vol.157, p.1(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jconhyd.2013.10.007 Byline: Marc Walther, Utku Solpuker, Norbert Bottcher, Olaf Kolditz, Rudolf Liedl, Frank W. Schwartz Abstract: We present a novel approach for the numerical simulation of the gelation of silicate solutions under density-dependent flow conditions. The method utilizes an auxiliary, not density-dependent solute that is subject to a linear decay function to provide temporal information that is used to describe the viscosity change of the fluid. By comparing the modeling results to experimental data, we are able to simulate the behavior and the gelation process of the injected solute for three different compositions, including long-term stability of the gelated area, and non-gelation of low concentrations due to hydro-dynamic dispersion. This approach can also be used for other types of solutes with this gelling property and is useful in a variety of applications in geological, civil and environmental engineering. Article History: Received 30 March 2013; Revised 11 October 2013; Accepted 22 October 2013
    Keywords: Silicates – Analysis ; Silicates – Models ; Flow (Dynamics) – Analysis ; Flow (Dynamics) – Models
    ISSN: 0169-7722
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Environmental Earth Sciences, 2014, Vol.72(10), pp.3827-3837
    Description: This paper evaluates the remediation potential of a salinized coastal aquifer by utilizing a scenario simulation. Therefore, the numerical model OpenGeoSys is first validated against analytical and experimental data to represent transient groundwater level development and variable density saline intrusion. Afterwards, a regional scale model with a three-dimensional, heterogeneous hydrogeology is calibrated for a transient state and used to simulate a best-case scenario. Water balances are evaluated in both the transient calibration and scenario run. Visualization techniques help to assess the complex model output providing valuable insight in the occurring density-driven flow processes. Furthermore, modeling and visualization results give information on the time scale for remediation activities and, due to limitations in data quality and quantity reveal potential for model improvement.
    Keywords: Groundwater modeling ; Density-dependent ; Saltwater intrusion ; OpenGeoSys ; Model validation benchmark ; Transient calibration ; Scenario simulation ; Remediation potential ; Visualization
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 5
    Language: English
    In: Environmental Earth Sciences, 11/2014, Vol.72(10), pp.3827-3837
    Description: This paper evaluates the remediation potential of a salinized coastal aquifer by utilizing a scenario simulation. Therefore, the numerical model OpenGeoSys is first validated against analytical and experimental data to represent transient groundwater level development and variable density saline intrusion. Afterwards, a regional scale model with a three-dimensional, heterogeneous hydrogeology is calibrated for a transient state and used to simulate a best-case scenario. Water balances are evaluated in both the transient calibration and scenario run. Visualization techniques help to assess the complex model output providing valuable insight in the occurring density-driven flow processes. Furthermore, modeling and visualization results give information on the time scale for remediation activities and, due to limitations in data quality and quantity reveal potential for model improvement. Copyright 2014 Springer-Verlag Berlin Heidelberg
    Keywords: Hydrogeology ; Environmental Geology ; Applications ; Aquifers ; Coastal Environment ; Computer Programs ; Data Processing ; Ground Water ; Numerical Models ; Opengeosys ; Pollution ; Remediation ; Salt Water ; Salt-Water Intrusion ; Simulation ; Three-Dimensional Models ; Visualization ; Water Pollution;
    ISSN: 1866-6280
    E-ISSN: 1866-6299
    Source: Springer (via CrossRef)
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  • 6
    Language: English
    In: Journal of Contaminant Hydrology, February 2014, Vol.157, pp.1-10
    Description: We present a novel approach for the numerical simulation of the gelation of silicate solutions under density-dependent flow conditions. The method utilizes an auxiliary, not density-dependent solute that is subject to a linear decay function to provide temporal information that is used to describe the viscosity change of the fluid. By comparing the modeling results to experimental data, we are able to simulate the behavior and the gelation process of the injected solute for three different compositions, including long-term stability of the gelated area, and non-gelation of low concentrations due to hydro-dynamic dispersion. This approach can also be used for other types of solutes with this gelling property and is useful in a variety of applications in geological, civil and environmental engineering.
    Keywords: Gelation ; Viscosity Change ; Density-Dependent ; Numerical Modeling ; Laboratory Experiment ; Opengeosys ; Engineering ; Environmental Sciences ; Geography
    ISSN: 0169-7722
    E-ISSN: 1873-6009
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  • 7
    Language: English
    In: Geoscientific Model Development Discussions, 09/22/2017, pp.1-28
    Description: Most of the current large scale hydrological models do not contain a physically-based groundwater flow component. The main difficulties in large-scale groundwater modeling include the efficient representation of unsaturated zone flow, the characterization of dynamic groundwater-surface water interaction and the numerical stability while preserving complex physical processes and high resolution. To address these problems, we propose a highly-scalable coupled hydrologic and groundwater model (mHM#OGS) based on the integration of two open-source modeling codes: the mesoscale hydrologic Model (mHM) and the finite element simulator OpenGeoSys (OGS). mHM#OGS is coupled using a boundary condition-based coupling scheme that dynamically links the surface and subsurface parts. Nested time stepping allows smaller time steps for typically faster surface runoff routing in mHM and larger time steps for slower subsurface flow in OGS. mHM#OGS features the coupling interface which can transfer the groundwater recharge and river baseflow rate between mHM and OpenGeoSys. Verification of the coupled model was conducted using the time-series of observed streamflow and groundwater levels. Moreover, we force the transient model using groundwater recharge in two scenarios: (1) spatially variable recharge based on the mHM simulations, and (2) spatially homogeneous groundwater recharge. The modeling result in first scenario has a slightly higher correlation with groundwater head time-series, which further validates the plausibility of spatial groundwater recharge distribution calculated by mHM in the mesocale. The statistical analysis of model predictions shows a promising prediction ability of the model. The offline coupling method implemented here can reproduce reasonable groundwater head time series while keep a desired level of detail in the subsurface model structure with little surplus in computational cost. Our exemplary calculations show that the coupled model mHM#OGS can be a valuable tool to assess the effects of variability in land surface heterogeneity, meteorological, topographical forces and geological zonation on the groundwater flow dynamics.
    Keywords: Geology;
    ISSN: Geoscientific Model Development Discussions
    E-ISSN: 1991-962X
    Source: CrossRef
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  • 8
    Language: English
    In: Advances in Water Resources, May 2017, Vol.103, pp.32-43
    Description: Due to limited availability of surface water, many arid to semi-arid countries rely on their groundwater resources. Despite the quasi-absence of present day replenishment, some of these groundwater bodies contain large amounts of water, which was recharged during pluvial periods of the Late Pleistocene to Early Holocene. These mostly fossil, non-renewable resources require different management schemes compared to those which are usually applied in renewable systems. Fossil groundwater is a finite resource and its withdrawal implies mining of aquifer storage reserves. Although they receive almost no recharge, some of them show notable hydraulic gradients and a flow towards their discharge areas, even without pumping. As a result, these systems have more discharge than recharge and hence are not in steady state, which makes their modelling, in particular the calibration, very challenging. In this study, we introduce a new calibration approach, composed of four steps: (i) estimating the fossil discharge component, (ii) determining the origin of fossil discharge, (iii) fitting the hydraulic conductivity with a pseudo steady-state model, and (iv) fitting the storage capacity with a transient model by reconstructing head drawdown induced by pumping activities. Finally, we test the relevance of our approach and evaluated the effect of considering or ignoring fossil gradients on aquifer parameterization for the Upper Mega Aquifer (UMA) on the Arabian Peninsula.
    Keywords: Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 9
    Language: English
    In: Geoscientific Model Development, June 1, 2018, Vol.11(5), p.1989
    Description: Most large-scale hydrologic models fall short in reproducing groundwater head dynamics and simulating transport process due to their oversimplified representation of groundwater flow. In this study, we aim to extend the applicability of the mesoscale Hydrologic Model (mHM v5.7) to subsurface hydrology by coupling it with the porous media simulator OpenGeoSys (OGS). The two models are one-way coupled through model interfaces GIS2FEM and RIV2FEM, by which the grid-based fluxes of groundwater recharge and the river-groundwater exchange generated by mHM are converted to fixed-flux boundary conditions of the groundwater model OGS. Specifically, the grid-based vertical reservoirs in mHM are completely preserved for the estimation of land-surface fluxes, while OGS acts as a plug-in to the original mHM modeling framework for groundwater flow and transport modeling. The applicability of the coupled model (mHM-OGS v1.0) is evaluated by a case study in the central European mesoscale river basin - N#xE4;gelstedt. Different time steps, i.e., daily in mHM and monthly in OGS, are used to account for fast surface flow and slow groundwater flow. Model calibration is conducted following a two-step procedure using discharge for mHM and long-term mean of groundwater head measurements for OGS. Based on the model summary statistics, namely the Nash-Sutcliffe model efficiency (NSE), the mean absolute error (MAE), and the interquartile range error (QRE), the coupled model is able to satisfactorily represent the dynamics of discharge and groundwater heads at several locations across the study basin. Our exemplary calculations show that the one-way coupled model can take advantage of the spatially explicit modeling capabilities of surface and groundwater hydrologic models and provide an adequate representation of the spatiotemporal behaviors of groundwater storage and heads, thus making it a valuable tool for addressing water resources and management problems.
    Keywords: Water Resource Management – Case Studies ; Water Resource Management – Analysis ; Water Resource Management – Models ; Rivers – Case Studies ; Rivers – Analysis ; Rivers – Models ; Groundwater Flow – Case Studies ; Groundwater Flow – Analysis ; Groundwater Flow – Models ; Water Resources – Case Studies ; Water Resources – Analysis ; Water Resources – Models ; Groundwater – Case Studies ; Groundwater – Analysis ; Groundwater – Models ; Hydrology – Case Studies ; Hydrology – Analysis ; Hydrology – Models
    ISSN: 1991-959X
    ISSN: 19919603
    E-ISSN: 19919603
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  • 10
    Language: English
    In: Environmental Earth Sciences, Nov, 2014, Vol.72(10), p.3881(19)
    Description: Byline: Lars Bilke (1), Thomas Fischer (1), Carolin Helbig (1), Charlotte Krawczyk (9), Thomas Nagel (1), Dmitri Naumov (7), Sebastian Paulick (4), Karsten Rink (1), Agnes Sachse (2), Sophie Schelenz (3), Marc Walther (6), Norihiro Watanabe (1), Bjorn Zehner (8), Jennifer Ziesch (9), Olaf Kolditz (1,5) Keywords: Virtual reality; Visualization; Computer graphics; Data exploration; Hydrological processes; Geotechnics; Seismic data; OpenGeoSys; VISLAB Abstract: Scientific visualization is an integral part of the modeling workflow, enabling researchers to understand complex or large data sets and simulation results. A high-resolution stereoscopic virtual reality (VR) environment further enhances the possibilities of visualization. Such an environment also allows collaboration in work groups including people of different backgrounds and to present results of research projects to stakeholders or the public. The requirements for the computing equipment driving the VR environment demand specialized software applications which can be run in a parallel fashion on a set of interconnected machines. Another challenge is to devise a useful data workflow from source data sets onto the display system. Therefore, we develop software applications like the OpenGeoSys Data Explorer, custom data conversion tools for established visualization packages such as ParaView and Visualization Toolkit as well as presentation and interaction techniques for 3D applications like Unity. We demonstrate our workflow by presenting visualization results for case studies from a broad range of applications. An outlook on how visualization techniques can be deeply integrated into the simulation process is given and future technical improvements such as a simplified hardware setup are outlined. Author Affiliation: (1) Department of Environmental Informatics, Helmholtz Centre for Environmental Research, Leipzig, Germany (2) Department of Catchment Hydrology, Helmholtz Centre for Environmental Research, Leipzig, Germany (3) Department of Monitoring and Exploration Technologies, Helmholtz Centre for Environmental Research, Leipzig, Germany (4) Department of Ecologial Modelling, Helmholtz Centre for Environmental Research, Leipzig, Germany (5) Chair of Applied Environmental System Analysis, Technische University at Dresden, Dresden, Germany (6) Institute for Groundwater Management, Technische University at Dresden, Dresden, Germany (7) Faculty of Mechanical and Energy Engineering, Leipzig University of Applied Sciences, Leipzig, Germany (8) Federal Institute for Geosciences and Natural Resources, Berlin, Germany (9) Leibniz Institute for Applied Geophysics, Hannover, Germany Article History: Registration Date: 07/10/2014 Received Date: 25/08/2014 Accepted Date: 06/10/2014 Online Date: 19/10/2014
    Keywords: Visualization (Computer) -- Case Studies ; Engineering Geology -- Case Studies ; Hydrology -- Case Studies ; Workflow Software -- Case Studies ; Graphics Software -- Case Studies
    ISSN: 1866-6280
    Source: Cengage Learning, Inc.
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