Rudolf Liedl

New experimental techniques for pneumatic tomographical determination of the flow and transport parameters of highly fractured porous rock samples

Abstract The investigation of flow and transport parameters in fractured porous material is difficult due to the high permeability contrast between the fracture networks and the porous material, and due to the question of the scale dependency of the parameters determined. Here experimental methods and new experimental equipment are presented using a pneumatic technique for the experimental tomographical investigation of highly fractured bench scale porous sandstone samples. The procedure allows a great deal of flexibility in the determination of the spatially variable flow and transport parameters and allows the question of scale to be addressed. Examples of the results gained from the application of these new techniques are given for both flow and transport parameter determination.

The IWAS-ToolBox: Software coupling for an integrated water resources management

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.

Modelling surfactant-enhanced remediation of polycyclic aromatic hydrocarbons

Abstract Within the framework of a comprehensive investigation concerning the use of surfactants to enhance the in situ remediation of polycyclic aromatic hydrocarbons (PAH) contaminations in the subsurface, SMART (Streamtube Model for Advective and Reactive Transport), a multicomponent transport model, was developed to study the processes (interactions) taking place when surfactants and PAH migrate through porous media as solutes. The model is an adaption of a Lagrangian method allowing for separate treatment of conservative transport and reactive processes. It accounts for the hydraulic as well as physico-chemical heterogeneity of porous aquifers. The system of processes implemented in the model has been shown to be able to represent the behaviour of PAH and surfactants in porous media at the laboratory scale. Here the transport model is applied to a simplified two-dimensional remediation scenario (field scale). It is shown how surfactants may influence the clean-up of PAH contaminated aquifers. Emphasis is put on the effect of hydraulic and physico-chemical aquifer properties on the coupled transport of PAH and surfactants.

Saltwater intrusion modeling: Verification and application to an agricultural coastal arid region in Oman

This paper deals with numerical modeling of density-dependent flow of saltwater intrusion in coastal 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 model 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.

Evaluation of thermal equations of state for CO2 in numerical simulations

Three commonly used thermal equations of state for carbon dioxide, as well as the ideal gas law, have been compared against a large number of measurement data taken from the literature. Complex equations of state reach a higher accuracy than simple ones. The inaccuracy of the density function can cause large errors in fluid property correlations, such as heat capacity or viscosity. The influence of this inaccuracy on the results of numerical simulations have been evaluated by two examples: The first one assumes isothermal gas expansion from a volume, while the second one considers heat transport along a fracture. For both examples, different equations of state have been utilized. The simulations have been performed on the scientific software platform OpenGeoSys. The difference among the particular simulation results is significant. Apparently small errors in the density function can cause considerably different results of otherwise identical simulation setups.

Assessing the saltwater remediation potential of a three-dimensional, heterogeneous, coastal aquifer system

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.

Land use/land cover classification and its change detection using multi-temporal MODIS NDVI data

Detailed analysis of Land Use/Land Cover (LULC) using remote sensing data in complex irrigated basins provides complete profile for better water resource management and planning. Using remote sensing data, this study provides detailed land use maps of the Lower Chenab Canal irrigated region of Pakistan from 2005 to 2012 for LULC change detection. Major crop types are demarcated by identifying temporal profiles of NDVI using MODIS 250 m × 250 m spatial resolution data. Wheat and rice are found to be major crops in rabi and kharif seasons, respectively. Accuracy assessment of prepared maps is performed using three different techniques: error matrix approach, comparison with ancillary data and with previous study. Producer and user accuracies for each class are calculated along with kappa coefficients (K). The average overall accuracies for rabi and kharif are 82.83% and 78.21%, respectively. Producer and user accuracies for individual class range respectively between 72.5% to 77% and 70.1% to 84.3% for rabi and 76.6% to 90.2% and 72% to 84.7% for kharif. The K values range between 0.66 to 0.77 for rabi with average of 0.73, and from 0.69 to 0.74 with average of 0.71 for kharif. LULC change detection indicates that wheat and rice have less volatility of change in comparison with both rabi and kharif fodders. Transformation between cotton and rice is less common due to their completely different cropping conditions. Results of spatial and temporal LULC distributions and their seasonal variations provide useful insights for establishing realistic LULC scenarios for hydrological studies.

Complexity vs. Simplicity: Groundwater Model Ranking Using Information Criteria

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 Kashyaps 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.

Modellbasierte Sickerwasserprognose für die Verwertung von Recycling-Baustoff in technischen Bauwerken

in this study, groundwater contamination from recycled demolition waste in road constructions is assessed using predictions of leachate concentrations. Numerical transport simulations are performed for three scenarios (a parking lot, a noise protection barrier, and road), and using a number of characteristic subsoils of germany, to estimate the breakthrough of different contaminant classes at the groundwater table. conservative tracer breakthrough times (btt) primarily depend on subsoil hydraulic properties, for organic pollutants KOc and subsoil Oc are the controlling parameters. Significant concentration reductions from dispersion only occur when source concentrations decrease prior to contaminant breakthrough. if source concentrations remain high for long periods relative to peak btt, concentration breakthrough is undamped. accounting for biodegradation reduces breakthrough concentrations significantly. For the “noise protection barrier” and “road” scenarios, capillary barrier effects cause the seepage water to partially bypass the recycling material. accounting for this bypass flow and spatial averaging across the constructions reduces concentrations by about 30–40 %.

Modelling surfactant influenced PAH migration

Abstract Within the framework of a comprehensive investigation concerning the use of surfactants to enhance the remediation of PAH contaminations in the subsurface, a multicomponent transport model was developed to study the processes (interactions) taking place when surfactants and PAH migrate through porous media as solutes. Based on a close co-operation with the laboratory investigations during model development only those processes that could be identified within laboratory experiments have been implemented in the model: (i) surfactant-micellization, (ii) surfactant sorption (formation of hemi- and admicelles), (iii) intra-particle diffusion of PAH, (iv) PAH sorption on hemi- or into admicelles, (v) solution of PAH within micelles. Furthermore, process-oriented descriptions are used to guarantee that only measurable parameters are needed as model input. In a first step column experiments with phenanthrene and the surfactant Terrasurf G50 (Danzer and Grathwohl, 1997, this issue) have been simulated by pure forward modelling in order to validate the conceptual model. Using independently measured parameters only the model is able to reproduce the breakthrough curves of both phenanthrene and Terrasurf G50 very well. Furthermore, the modelling results provide evidence that not only PAH sorption but also the sorption of surfactants may be limited by diffusion. Based upon these results a new conceptual model of the processes involved in the coupled transport of PAH and surfactants has been developed.