With the help of Schlieren images (line-integral convolution visualization technology) the flow paths can be described clearly and graphically appealing using the flow rates in a potential field. Thus, catchment areas can be estimated quickly also in 3D models, where physically no stream lines are to be determined. The colouring of the Schlieren depends on the problem and is based on freely selectable input or result data (i.e. temperatures, potentials, ground level, ...).