Abstract : Pesticides, which have been extensively used in agriculture, have become a major environmental issue, especially regarding surface and ground water contamination. Of particular importance are vegetated farm drainage ditches, which can play an important role in the mitigation of pesticide contamination by adsorption onto ditch bed substrates. This role is however poorly understood, especially regarding the influence of hydrodynamic parameters, which make it difficult to promote best management practice of these systems. We have assessed the influence of three of these parameters on the transfer and adsorption of selected pesticides (isoproturon, diuron, tebuconazole and azoxystrobin) into the bed substrate by performing experiments with a tilted experimental flume, using hemp fibres as a standard of natural organic substrates that are found at the bottom of agricultural ditches. There were: 1, the speed of the surface water flow; 2, the submergence; and 3, the geometrical characteristics of the bed forms. The results show that the transfer of the pesticides from the surface water flow into the bed substrate is favoured, both regarding the amounts transferred into the bed substrate and the kinetics of the transfer, when the surface water speed and the submergence increase, and when the bed forms are made of rectangular shapes. The extrapolation of the flume data over a distance of several hundred meters, suggests that an interesting possibility for improving the mitigation of pesticides in ditches would be to increase the submergence and to favour bed forms which tend to enhance perturbations and subsequent infiltration of the surface water flow.