Estimates of pesticide contributions to surface water by spray drift can be made by using the Rautmann-Ganzelmeier curves (Rautmann et al., 2001), which describe the deposition of pesticides on a water course depending on the distance between the boundary of the treated surface and the water course.
The functions of Ganzelmeier-Rautmann are a model of deposition on a body of water and not the outputs from the field (it is difficult to calculate all the outputs by drift of the plot). So a receptacle, here a stream is always needed to do drift calculations.
The Ganzelmeier-Rautmann curves are functions adjusted to experimental data points and give the deposits on the surface (in the form of a relative surface concentration, that is, in percent of the application rate on the plot) depending on the distance of the treated surface.
It should be noted that the curves reflect an application without technique reducing drift, but which observes good agricultural professional practice (wind speed ≤ 5 m/s, tractor speed ≤ 8 km/h, spray bar in position not too high etc.). If good professional practices are not observed (which is illegal in Germany, where the experiments were done), the resulting drift may be higher.