Dr.-Ing. Leopold Stadler

Simulating the flow of water and soil air in macroporous soils is important for many technical and scientific problems. In this thesis, two different modelling concepts for simulating two-phase flow (water/gas) in macroporous soils are presented and their underlying numerical methods and implementation are discussed. Python and Embedded Python were used to allow rapid software development and extension of existing simulation programs. Further, an interface (XML-RPC) for the coupling of different computer programs is presented.

The first modelling concept allows to simulate the flow in a single macropore and the surrounding soil matrix and the water and gas transfer between the matrix and the macropore. Numerical results are compared with existing measurements and the fluxes between the macropore and the matrix are analyzed. Mathematical optimization was applied for finding reasonable soil hydraulic parameters.

The second modelling concept is an extension of the widely used Richards dual-permeability model. For such models, the soil is divided into a matrix and macropore continuum. The flow in both continua is described with separate balance equations. Transfer terms are used to compute the mass exchange between the matrix and macropores. While the classical Richards dual-permeability models only allows the simulation of water flow, the presented two-phase dual-permeability model also considers the soil air. Similar model concepts exist for fractured rocks. The presented studies show that the soil air can have a strong influence on the flow and infiltration of water. Hence Richards dual-permeability models may fail to properly describe the flow of water. Differences between the Richards model and the two-phase flow model were mainly observed when the soil air was trapped inside the matrix and the transfer between matrix and macropores was hindered by the macropore surface.

The application range of the new two-phase dual-permeability model was tested by simulating the flow processes in a macroporous hill slope. Special dynamic boundary conditions were developed to simulate the infiltration and exfiltration of water. Water flow occurred mainly in the macropores, the matrix acted as a storage volume. From the studies it was concluded that evapotranspiration should be taken into account for long term simulations.