Development of a numerical reactive transport modelling framework - Concept & Case Studies

Civilization and in particular agriculture worldwide depends on the availability of clean freshwater resources stored in the underlying soil and aquifer systems. Unfortunately, water quality is often deteriorating, which is e.g. due to the extensive use of fertilizers or pesticides in agriculture or infiltrating waste water from cities and industries. All groundwater bodies commonly discharge into the nearby surface-water bodies like streams, lakes, or springs, and soil water is a direct water source for the biosphere. Therefore, bio-hydro-geochemical reaction systems along flow paths of the unsaturated as well as the saturated zone can have a strong impact on aquatic and terrestrial ecosystems.

The simulation of such reactive transport problems in different hydrological compartments can help to understanding the comprehensive processes chain. One way to evaluate the water quality in space and time is to model the mass transport in soil and/or groundwater together with the contemporaneous chemical reactions numerically. Such physical and bio- hydro- geochemical driven forward simulations are usually solved by standard finite differences, finite element or finite volume methods, but simulating these scenarios at catchment scales is a challenging task due to the extreme computational load, numerical stability issues and different scale-dependencies.

The main focus of the present study is the numerical simulation of reactive transport processes in heterogeneous porous media at large scales, i.e. from field scale, over hill slopes towards catchment scale. The objective of the study is, to develop a robust modelling framework which allows to identify appropriate levels of heterogeneity as well as the possibly dominating structural features (e.g. S-shaped clay lenses) with respect to specific reaction systems. The presented modelling framework will describe the functional interaction of different numerical methods and high performing computing (HPC) techniques by the use of exemplary case studies. The concept includes different numerical coupling concepts e.g. operator splitting, global implicit approaches, particle tracking method, or tool couplings together with an OpenMPI parallelization scheme for reactive transport simulations on HPC-Cluster infrastructures.