In the Erlenbach experimental basin in central Switzerland the actual sediment transport has been measured for more than 10 years with socalled hydrophones. These measurements show that the relation between runoff and sediment transport is nonlinear and that its complexity cannot be described by simple sediment transport models. Therefore a new concept, the concept PROBLOAD is proposed. The probable sediment transport is described by a Monte-Carlo simulation based on assumptions on the driving and retaining forces acting on a grain on the bed surface. The concept seems to be able to describe the behaviour of sediment transport in a steep mountain torrent.