Rudolf Liedl

Technische Universität Dresden, Dresden, Saxony, Germany

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Publications (86)117.47 Total impact

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    ABSTRACT: In the last ten years (approximately) a lot of natural attenuation scenarios have been modeled under the assumption that the degradation of pollutants occurs mainly at the reaction front. This was particularly facilitated by using numerical methods which readily covers a wide range of different hydrogeological scenarios to predict associated plume length. In contrast, due to experimental difficulties, only part of the scenarios has so far been simulated in laboratory experiments in order to assess the suitability of the models under controlled conditions. This paper deals with the design and evaluation of natural attenuation scenario at laboratory scale in a tank experiment which is based on a vertical 2D experiment (tank dimension 200 cm * 2 cm * 15 cm). The study aims at the maximum spreading of electron donors (contaminant) reacting with the vertically entering electron acceptors (e.g. oxygen). In the experiment, this scenario was simulated by a base-acid pair with pH = 11.3 and pH = 2, respectively. An indicator mixing with both acid and base was used to visualize the reaction front. Glass beads (diameter 1.55 mm to 1.88 mm) was used as porous media. Experiments were evaluated after reaching steady conditions.
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    Environmental earth sciences 04/2014; · 1.45 Impact Factor
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    ABSTRACT: Aquifer storage and recovery (ASR) methods are increasingly used to overcome the temporal imbalance between water demand and availability. Common ASR recharge methods utilize large-diameter injection wells or surface infiltration basins and trenches, and can be costly to implement. A new low-cost ASR recharge method is currently being developed. This approach is based on recharge via gravity in small-diameter wells installed with direct-push (DP) technology. Numerical modeling is used here to assess the potential of this new approach under conditions commonly faced in field settings. The primary objective is to investigate if a battery of small-diameter DP wells can serve as a viable alternative to a surface basin under typical field conditions, while the secondary objective is to assess which subsurface parameters have the greatest control on DP well performance. Simulation results indicate that gravity recharge via small-diameter wells appears to have a distinct advantage over recharge via surface infiltration basins. For example, two 0.05-m shallow vadose-zone wells with 9-m screens can recharge water at a greater rate than a 60 m2 basin. Also, results reveal that, contrary to an infiltration basin, the recharge rate in a DP well has a much stronger dependence on the horizontal component of hydraulic conductivity than on the vertical component. Moreover, near-surface layers of low hydraulic conductivity, which can significantly reduce the recharge capacity of a surface basin, have a relatively small impact on the recharge capacity of a well as long as a significant portion of the well screen is installed below those layers. Given that installation and operation costs can be low in comparison to common ASR recharge methods, this new approach appears to have great potential for recharging good quality water in shallow unconsolidated aquifers. A field investigation has recently been initiated to follow up the findings of this simulation assessment.
    Journal of Hydrology. 01/2014; 517:54–63.
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    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.
    Journal of contaminant hydrology 11/2013; 157C:1-10. · 2.01 Impact Factor
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    ABSTRACT: A groundwater model characterized by a lack of field data about hydraulic model parameters and boundary conditions combined with many observation data sets for calibration purpose was investigated concerning model uncertainty. Seven different conceptual models with a stepwise increase from 0 to 30 adjustable parameters were calibrated using PEST. Residuals, sensitivities, the Akaike information criterion (AIC and AICc), Bayesian information criterion (BIC), and Kashyap's information criterion (KIC) were calculated for a set of seven inverse calibrated models with increasing complexity. Finally, the likelihood of each model was computed. Comparing only residuals of the different conceptual models leads to an overparameterization and certainty loss in the conceptual model approach. The model employing only uncalibrated hydraulic parameters, estimated from sedimentological information, obtained the worst AIC, BIC, and KIC values. Using only sedimentological data to derive hydraulic parameters introduces a systematic error into the simulation results and cannot be recommended for generating a valuable model. For numerical investigations with high numbers of calibration data the BIC and KIC select as optimal a simpler model than the AIC. The model with 15 adjusted parameters was evaluated by AIC as the best option and obtained a likelihood of 98%. The AIC disregards the potential model structure error and the selection of the KIC is, therefore, more appropriate. Sensitivities to piezometric heads were highest for the model with only five adjustable parameters and sensitivity coefficients were directly influenced by the changes in extracted groundwater volumes.
    Ground Water 06/2013; · 2.13 Impact Factor
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    ABSTRACT: Thermal management of aquifers requires knowledge on interactions and heat transport processes not only on a local but also on a more regional scale. Therefore, prediction of temperature developments due to thermal use and other anthropogenic impacts necessitate the use of large scale numerical models based on field temperature measurements. This contribution presents different modelling strategies for the thermal management of shallow rural and urban groundwater bodies. Depending on the settings and the relevant management topics different boundary conditions have to be considered. Whereas, thermal regimes within rural groundwater bodies primarily are governed by natural boundaries and the interaction with the atmosphere, in urban areas also the influences of urbanization and heated subsurface constructions have to be considered. Therefore, the setup of modelling tools as basis for the thermal management of groundwater bodies in different settings requires different interaction processes to be focused on. The study is illustrated by selected examples of a rural groundwater body located in the "Leibnitzer Feld" (Austria) and an urban groundwater body located in the city of Basel (Switzerland). The two case studies differ in their respective hydro-geological setting, above all in the vertical extents of the saturated and unsaturated zone. Therefore, specific modelling approaches are used to focus on a reliable description of the main governing impacts. The regional models evaluate current and future thermal use of the groundwater bodies and highlight the advantages arising from a regional view of heat transport processes.
    Poster. 04/2013;
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    ABSTRACT: Karst aquifers are characterized by highly conductive conduit flow paths embedded in a less conductive fissured and fractured matrix resulting in strong permeability contrasts with structured heterogeneity and anisotropy. Groundwater storage occurs predominantly in the fissured matrix. Hence, most karst models assume quasi steady-state flow in conduits neglecting conduit associated drainable storage (CADS). The concept of CADS considers storage volumes, where karst water is not part of the active flow system but rather hydraulically connected to conduits (for example karstic voids and large fractures). The disregard of conduit storage can be inappropriate when direct water abstraction from karst conduits occurs, e.g. large scale pumping. In such cases, CADS may be relevant. Furthermore, the typical fixed head boundary condition at the karst outlet can be inadequate for water abstraction scenarios because unhampered water inflow is possible. The objective of this paper is to analyze the significance of CADS and flow-limited boundary conditions on the hydraulic behavior of karst aquifers in water abstraction scenarios. To this end, the numerical hybrid model MODFLOW-2005 Conduit Flow Process Mode 1 (CFPM1) is enhanced to account for CADS. Additionally, a fixed-head limited-flow (FHLQ) boundary condition is added that limits inflow from constant head boundaries to a user-defined threshold. The affect and proper functioning of these modifications is demonstrated by simplified model studies. Both enhancements, CAD storage and the FHLQ boundary, are shown to be useful for water abstraction scenarios within karst aquifers. An idealized representation of a large-scale pumping test in a karst conduit is used to demonstrate that the enhanced CFPM1 is potentially able to adequately represent water abstraction processes in both the conduits and the matrix of real karst systems.
    Hydrology and Earth System Sciences Discussions 04/2013; 10(4):4463-4487. · 3.59 Impact Factor
  • Workshop on Visualisation in Environmental Sciences (EnvirVis); 01/2013
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    ABSTRACT: Die Verunreinigung des Grundwassers mit organischen Schadstoffen ist weltweit nach wie vor ein Problem. Für die Auswahl einer geeigneten Sanierungsmethode ist eine Erstabschätzung des Gefährdungspotenzials des kontaminierten Standortes unerlässlich. Dies ist unter Verwendung von analytischen und numerischen Verfahren möglich, welche Schadstoffausbreitungen prognostizieren können. Für eine erste Bewertung von kontaminierten Standorten wurde das MS-Excel© -Werkzeug Natural-Attenuation-Fahnenlängenabschätzung, kurz „NAFLA“ entwickelt. „NAFLA“ ermöglicht die unkomplizierte und effiziente Berechnung und den Vergleich einiger analytischer Modelle welche für die Abschätzung von maximalen Fahnenlängen unter stationären Bedingungen entwickelt wurden. Diese Methoden variieren in Quellgeometrie und Modellorientierung sowie in der Modellannahme für die (bio)chemischen Reaktionen im Modellbereich. Die Weiterentwicklung und Integration zusätzlicher analytischer Modelle ist möglich. In dieser Mitteilung wird die Entwicklung von „NAFLA“ dargestellt, seine Nutzung aufgezeigt und Benutzerhinweise gegeben. Die Anwendung dieses Tools wird insbesondere in der studentischen Ausbildung, für Behörden und Beratungsunternehmen gesehen.
    Grundwasser 01/2013; 18(1). · 0.94 Impact Factor
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    ABSTRACT: This paper deals with numerical modeling of groundwater systems. We present the implementation of an approach to solve a moving boundary problem for a dynamic water table within an invariant finite element mesh. The modeling software is successfully validated against laboratory experiment data for an unconfined, density-dependent benchmark. The validated software is applied to a regional-scale study area and sufficiently calibrated for a steady state of pre-development conditions. Transient mass transport scenario simulations show good concordance with salinity measurements satisfyingly supporting the model setup.
    Journal of Computational and Applied Mathematics 12/2012; 236(18):4798-4809. · 0.99 Impact Factor
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    ABSTRACT: In this work, we present a framework for numerical modeling of CO2 injection into porous media for enhanced gas recovery (EGR) from depleted reservoirs. Physically, we have to deal with non-isothermal, compressible gas flows resulting in a system of coupled non-linear PDEs. We describe the mathematical framework for the underlying balance equations as well as the equations of state for mixing gases. We use an object-oriented finite element method implemented in C++. The numerical model has been tested against an analytical solution for a simplified problem and then applied to CO2 injection into a real reservoir. Numerical modeling allows to investigate physical phenomena and to predict reservoir pressures as well as temperatures depending on injection scenarios and is therefore a useful tool for applied numerical analysis.
    Journal of Computational and Applied Mathematics 12/2012; 236(18):4933–4943. · 0.99 Impact Factor
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    ABSTRACT: A groundwater model characterized by a lack of field data to estimate hydraulic model parameters and boundary conditions combined with many piezometric head observations was investigated concerning model uncertainty. Different conceptual models with a stepwise increase from 0 to 30 adjustable parameters were calibrated using PEST. Residuals, sensitivities, the Akaike Information Criterion (AIC), and the likelihood of each model were computed. As expected, residuals and standard errors decreased with an increasing amount of adjustable model parameters. However, the model with only 15 adjusted parameters was evaluated by AIC as the best option with a likelihood of 98%, while the uncalibrated model obtained the worst AIC value. Computing of the AIC yielded the most important information to assess the model likelihood. Comparing only residuals of different conceptual models was less valuable and would result in an overparameterization of the conceptual model approach. Sensitivities of piezometric heads were highest for the model with five adjustable parameters reflecting also changes of extracted groundwater volumes. With increasing amount of adjustable parameters piezometric heads became less sensitive for the model calibration and changes of pumping rates were no longer displayed by the sensitivity coefficients. Therefore, when too many model parameters were adjusted, these parameters lost their impact on the model results. Additionally, using only sedimentological data to derive hydraulic parameters resulted in a large bias between measured and simulated groundwater level.
    Hydrology and Earth System Sciences Discussions 08/2012; 9(8):9687-9714. · 3.59 Impact Factor
  • Andy Philipp, Thomas Wöhling, Rudolf Liedl
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    ABSTRACT: Coming from the zero inertia (ZI) equations, an analytical model to describe sheet flow phenomena with a special focus on rainfall runoff processes is developed. A slight modification of the ZI equations, which draws upon the concept of a momentum-representative cross-section of the moving water body, leads—after comprehensive mathematical calculus—to an analytical solution describing essentially one-dimensional, shallow overland flow. In a test series, the analytical ZI model is applied together with three numerical models, one based on the Saint-Venant equations, one on the kinematic wave equations, and another one on diffusion wave equations. The test application refers to a typical rainfall runoff situation, i.e., rather shallow overland flow on a hillslope as a consequence of excess rainfall. Contrary to the analytical model, the comparative analysis clearly shows the difficulties of the numerical solutions in terms of exactness and robustness when approaching typical shallow water depths. This problem of numerical models is tackled by applying small time and space discretization, which, however, comes along with higher CPU execution times. Besides the good computational efficiency and freedom of any numerical inconvenience, the new analytical model outperforms the numerical models for typical overland flow simulations. This particularly refers to a highly satisfactory fulfillment of the mass balance and a nearly perfect match of peak flow rates.
    Journal of Hydraulic Engineering 05/2012; 138(5):391-399. · 1.28 Impact Factor
  • ModelCare2011, Models - Repositories of Knowledge; 01/2012
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    ABSTRACT: Numerical modeling of interacting flow and transport processes between different hydrological compartments, such as the atmosphere/land surface/vegetation/soil/groundwater systems, is essential for understanding the comprehensive processes, especially if quantity and quality of water resources are in acute danger, like e.g. in semi-arid areas and regions with environmental contaminations. The computational models used for system and scenario analysis in the framework of an integrated water resources management are rapidly developing instruments. In particular, advances in computational mathematics have revolutionized the variety and the nature of the problems that can be addressed by environmental scientists and engineers. It is certainly true that for each hydro-compartment, there exists many excellent simulation codes, but traditionally their development has been isolated within the different disciplines. A new generation of coupled tools based on the profound scientific background is needed for integrated modeling of hydrosystems. The objective of the IWAS-ToolBox is to develop innovative methods to combine and extend existing modeling software to address coupled processes in the hydrosphere, especially for the analysis of hydrological systems in sensitive regions. This involves, e.g. the provision of models for the prediction of water availability, water quality and/or the ecological situation under changing natural and socio-economic boundary conditions such as climate change, land use or population growth in the future. KeywordsCoupling–Modeling–Surface–subsurface–Soil–root water flow–Reactive transport–Density-dependent flow
    Environmental earth sciences 01/2012; 65(5):1367-1380. · 1.45 Impact Factor
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    ABSTRACT: Water resources management schemes generally imply the availability of a spectrum of various sources of water with a variability of quantity and quality in space and time, and the availability and suitability of storage facilities to cover various demands of water consumers on quantity and quality. Aquifers are generally regarded as suitable reservoirs since large volumes of water can be stored in the subsurface, water is protected from contamination and evaporation and the underground passage assists in the removal of at least some groundwater contaminants. Favorable aquifer properties include high vertical hydraulic conductivities for infiltration, large storage coefficients and not too large hydraulic gradients / conductivities. The latter factors determine the degree of discharge, i.e. loss of groundwater. Considering the above criteria, fractured and karstified aquifers appear to not really fulfill the respective conditions for storage reservoirs. Although infiltration capacity is relatively high, due to low storativity and high hydraulic conductivities, the small quantity of water stored is rapidly discharged. However, for a number of specific conditions, even karst aquifers are suitable for groundwater management schemes. They can be subdivided into active and passive management strategies. Active management options include strategies such as overpumping, i.e. the depletion of the karst water resources below the spring outflow level, the construction of subsurface dams to prevent rapid discharge. Passive management options include the optimal use of the discharging groundwater under natural discharge conditions. System models that include the superposition of the effect of the different compartments soil zone, epikarst, vadose and phreatic zone assist in the optimal usage of the available groundwater resources, while taking into account the different water reservoirs. The elaboration and implementation of groundwater protection schemes employing well established vulnerability assessment techniques ascertain the respective groundwater quality. In this paper a systematic overview is provided on karst groundwater management schemes illustrating the specific conditions allowing active or passive management in the first place as well as the employment of various types of adapted models for the design of the different management schemes. Examples are provided from karst systems in Israel/Palestine, where a large 4000sqkm basin is being managed as a whole, the South of France, where the Lez groundwater development scheme illustrates the optimal use of overpumping from the conduit system, providing additional water for the City of Montpellier during dry summers and at the same time increasing recharge and assisting in the mitigation of flooding during high winter discharge conditions. Overpumping could be an option in many Mediterranean karst catchments since karst conduit development occurred well below today's spring discharge level. Other examples include the construction of subsurface dams for hydropower generation in the Dinaric karst and reduction of discharge. Problems of leakage and general feasibility are discussed.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Well-developed karst aquifers consist of highly conductive conduits and a relatively low permeability fractured and/or porous rock matrix and therefore behave as a dual-hydraulic system. Groundwater flow within highly permeable strata is rapid and transient and depends on local flow conditions, i.e., pressurized or nonpressurized flow. The characterization of karst aquifers is a necessary and challenging task because information about hydraulic and spatial conduit properties is poorly defined or unknown. To investigate karst aquifers, hydraulic stresses such as large recharge events can be simulated with hybrid (coupled discrete continuum) models. Since existing hybrid models are simplifications of the system dynamics, a new karst model (ModBraC) is presented that accounts for unsteady and nonuniform discrete flow in variably saturated conduits employing the Saint-Venant equations. Model performance tests indicate that ModBraC is able to simulate (1) unsteady and nonuniform flow in variably filled conduits, (2) draining and refilling of conduits with stable transition between free-surface and pressurized flow and correct storage representation, (3) water exchange between matrix and variably filled conduits, and (4) discharge routing through branched and intermeshed conduit networks. Subsequently, ModBraC is applied to an idealized catchment to investigate the significance of free-surface flow representation. A parameter study is conducted with two different initial conditions: (1) pressurized flow and (2) free-surface flow. If free-surface flow prevails, the systems is characterized by (1) a time lag for signal transmission, (2) a typical spring discharge pattern representing the transition from pressurized to free-surface flow, and (3) a reduced conduit-matrix interaction during free-surface flow.
    Water Resources Research 11/2011; 47(11):11503-. · 3.15 Impact Factor
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    ABSTRACT: Transport of contaminants degrades natural resourcesPlume length formula can be used to quantify contaminant transportA 3D analytical Model is more realistic than so far known 2D models
    Water Resources Research 01/2011; 47(8). · 3.15 Impact Factor
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    Andy Philipp, Gerd H. Schmitz, Rudolf Liedl
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    ABSTRACT: A surge running down a dry wadi bed as a consequence of a controlled water release from a reservoir—e.g., for artificial groundwater recharge—represents a free boundary problem. After some time, when aiming for groundwater recharge, the infiltration equals inflow and thus forms a kind of “standing” wave. The numerical solution of such phenomena generally involves considerable problems. For avoiding the numerical inconvenience resulting from the complex interacting surface/subsurface flow, we present an analytical solution of the slightly modified zero-inertia (ZI) equations. The development introduces a momentum-representative cross section for portraying the transient development of momentum and refers to a channel with constant slope, irregular geometry, and a permeable channel bed with significant infiltration. Due to the structure of the solution, any arbitrary infiltration model can be used for quantifying the infiltration losses. For both synthetic prismatic and nonprismatic test channels, the robust and easy-to-use analytical ZI model shows an excellent match with the results of a comparative numerical simulation. Finally, the ZI model is employed for simulating a surge flow downstream of the Wadi Ahin groundwater recharge dam (Oman), in order to perform a scenario for artificial groundwater recharge in a natural wadi channel reach. This realistic application illustrates the potential of the new approach by even computing an almost standing wave and shows its applicability for an accurate and robust evaluation of release strategies.
    Journal of Hydraulic Engineering 05/2010; 136(5):290-298. · 1.28 Impact Factor

Publication Stats

790 Citations
117.47 Total Impact Points

Institutions

  • 2007–2014
    • Technische Universität Dresden
      • Institut für Grundwasserwirtschaft
      Dresden, Saxony, Germany
  • 2013
    • Bauhaus Universität Weimar
      Weimar, Thuringia, Germany
  • 2003–2010
    • Georg-August-Universität Göttingen
      • Geoscience Centre
      Göttingen, Lower Saxony, Germany
    • The University of Edinburgh
      • School of GeoSciences
      Edinburgh, Scotland, United Kingdom
  • 1998–2009
    • University of Tuebingen
      • Group of Applied Geosciences
      Tübingen, Baden-Württemberg, Germany
  • 2008
    • Karl-Franzens-Universität Graz
      • Institute of Earth Sciences
      Graz, Styria, Austria
  • 2006
    • Heriot-Watt University
      Edinburgh, Scotland, United Kingdom