The current work presents the modeling of soil moisture distribution and routing in two small headwater catchments within the catchment of Lake Greifensee (Switzerland). It aims at localizing saturated areas that contribute to surface runo and areas that tend to preferential
ow through tile drains. Thereby it shows an option to determine areas that produce diffuse herbicide losses to surface water. The transferability of the used model parameterization is tested concerning another simulation period on the one hand and another catchment on the other hand. For model veri cation the simulation results are compared to field data (discharge and atrazine losses) in the study catchments for the year 1999. The model evaluation is done concerning the temporal dynamic of water discharges and the spatial pattern of saturation and runoff. Furthermore sensitivity and identifiability analyses detect the main influence factors on the simulation results and the problems regarding to lack of data. Parameter estimations help to improve the simulations. They serve as a starting point to clarify which parameter values may be different for a better model representation of the system. Finally conclusions are drawn concerning the possibilities of the model to determine
areas contributing to diffuse herbicide loss.