"Effects of Grid Size and Upscaling for Finite-Difference Flow and Transport Model"
In the framework of the BMBF research project GLOWA-Danube , the long-term evolution of the water cycle for the German catchment area of the river Danube has to be determined. The part performed at Institute for Hydraulics, of the Stuttgart University, is the development of a finite-difference groundwater flow and transport model on a grid with a cell size of 1 km x 1 km. Modeling transport of nitrates on such a coarse grid is a new and challenging problem. The aim of this master thesis was to compare the results obtained by using different cell sizes, which differ from each other due to numerical dispersion, and to investigate problems emerging from the process of upscaling. The transport of nitrates was assumed to be purely advective one. The flow model was a steady-state one, and the transport model was transient.
The main work was carried out on conceptual models, simple models that are built in such a way as to allow a focused analysis of one or more of its components. One-dimensional and two-dimensional models were investigated. A case study for the Leutkircher Heide and Aitrachtal aquifer, located in the southeastern part of Baden-Württemberg, was also investigated. Every studied case was modeled on grids of different size, comparing the results and trying to understand the evolution of the differences between the solution obtained. The assumption was done that the results calculated on the finest grid are closest to the real ones.