Novel evaporation experiment to determine soil hydraulic properties

A novel experimental approach to determine soil hydraulic material properties for the dry and very dry range is presented. Evaporation from the surface of a soil column is controlled by a constant flux of preconditioned air and the resulting vapour flux is measured by infrared absorption spectroscopy. The data are inverted under the assumptions that (i) the simultaneous movement of water in the liquid and vapour is represented by Richards' equation with an effective hydraulic conductivity and that (ii) the coupling between the soil and the well-mixed atmosphere can be modelled by a boundary layer with a constant transfer resistance. The optimised model fits the data exceptionally well. Remaining deviations during the initial phase of an experiment are thought to be well-understood and are attributed to the onset of the heat flow through the column which compensates the latent heat of evaporation

Numerical simulation of growth of Escherichia coli in unsaturated porous media

A model for the aerobic and anaerobic growth of Escherichia coli (HB101 K12 pGLO) depending on the concentration of oxygen and DOC as substrate has been developed based on laboratory batch experiments. Using inverse modelling to obtain optimal sets of parameters, it could be shown that a model based on a modified double Contois kinetic can predict cell densities, organic carbon utilisation, oxygen transfer and utilisation rates for a large number of experiments under aerobic and anaerobic conditions with a single unique set of parameters. The model was extended to describe growth of E. coli in unsaturated porous media, combining diffusion, phase exchange and microbiological growth. Experiments in a Hele-Shaw cell, filled with quartz sand, were conducted to study bacterial growth in the capillary fringe above a saturated porous medium. Cell density profiles in the Hele-Shaw cell were predicted with the growth model and the parameters from the batch experiments without any further calibration. They showed a very good qualitative and quantitative agreement with cell densities determined from samples taken from the Hele-Shaw cell by re-suspension and subsequent counting. Thus it could be shown, that it is possible to successfully transfer growth parameters from batch experiments to porous media for both aerobic and anaerobic conditions.Comment: Minor changes in conclusions, results unchange

Novel evaporation experiment to determine soil hydraulic properties

International audienceA novel experimental approach to determine soil hydraulic material properties for the dry and very dry range is presented. Evaporation from the surface of a soil column is controlled by a constant flux of preconditioned air and the resulting vapour flux is measured by infrared absorption spectroscopy. The data are inverted under the assumptions that (i) the simultaneous movement of water in the liquid and vapour is represented by Richards' equation with an effective hydraulic conductivity and that (ii) the coupling between the soil and the well-mixed atmosphere can be modelled by a boundary layer with a constant transfer resistance. The optimised model fits the data exceptionally well. Remaining deviations during the initial phase of an experiment are thought to be well-understood and are attributed to the onset of the heat flow through the column which compensates the latent heat of evaporation

Contributions to the large-scale Simulation of Flow and Transport in Heterogeneous Porous Media

Powerful software tools for the sequential and parallel simulation of water and solute transport in strongly heterogeneous porous media are developed based on an extensive discussion of the involved processes, as well as of numerical and implementation aspects. The tools are applied to study problems involving parameter estimation in heterogeneous porous media, virtual soil systems and dynamic effects in heterogeneous soils. The excelent scalability of the numerical solver for both water as well as solute transport is investigated on BlueGene/P and /Q type supercomputers. As file transfer can be a bottleneck for large-scale simulations it is analysed carefully, obtaining near optimal data transfer rates with data sets of up to 17.5 Terabyte

Do effective properties for unsaturated weakly layered porous media exist? An experimental study

International audienceIn a multi-step outflow experiment we found that a weak heterogeneity within a sand column prevents the estimated effective hydraulic parameters from being unique. We compared vertical water content profiles calculated from these parameters with profiles measured by x-ray attenuation. A layered material model based on x-ray data was able to reproduce the outflow curve and also the water content distribution inside the column. We also calculated effective parameters for the layered model turned upside down and obtained large differences to the set of values of the original sample

Coupled transport in natural porous media

As the interactions between transport processes are important for a number of interesting systems, a set of partial differential equations and appropriate parameter functions for the study of coupled water, heat, gas and solute transport was formulated and a state of the art computer model for the numerical solution of the equation system was created. A new phase pressure/partial pressure formulation for the coupled transport of liquid and gas phase was developed. The model was used to simulate the water and energy dynamics of a permafrost soil. A good qualitative agreement was achieved. Differences between modeled and measured data could be explained with heterogeneity in combination with the model's sensitivity to a change in hydraulic parameters. Water vapor and solute transport had no effect on the simulation result but transport of liquid water proved to be an important heat transfer process near 0 °C. The impact of the chosen parameterization and model on the simulation of a multistep outflow experiment was analyzed. Differences between a model based on Richards' equation and a twophase model only occurred when the Brooks-Corey parameterization was used. The results of the twophase model showed a retarded drainage and a hysteresis during imbibation which is in good agreement with experimental results