The GROWA98 model for water balance analysis in large river basins—the river Elbe case study

An area differentiated water balance analysis in the river Elbe basin (German part) for the hydrological period 1961–1990 was carried out using the GROWA98 model. The mean long-term total runoff was modelled as a function of the regional interaction of the site conditions climate, soil, geology, topography and land use. The total runoff was separated into the direct runoff (interflow and surface runoff) and groundwater runoff (base flow) using base-flow indices, depending on area characteristics (e.g. geology, depth for groundwater). In this way, the regional dominant runoff components, i.e. pathways for the displacement of nutrients from soil to surface water were identified. The model results were validated by comparing the calculated runoff levels with measured data from 120 sub-basins of the river Elbe-catchment area. In general, the differences between modelled and measured runoff values were less than 15%, indicating the reliability of the chosen procedure. This allows further model applications, e.g. for the quantification of the diffuse nutrient input into groundwater and surface waters differentiated to the runoff components.