A sediment routing model called SETRAC has been developed to simulate bedload transport in torrents and mountain streams. SETRAC is the acronym for Sediment Transport in Alpine Catchments. Flow resistance is modelled using an approach proposed by Smart and Jaggi, and bedload transport is predicted with an equation by Rickenmann. Form roughness losses are accounted for by an empirical approach which is based on flow resistance observations in mountain streams. It is possible to compute fractional bedload transport taking grain sorting effects into account. Flow hydrographs are routed through the channel network by using the kinematic wave approach. An application of the model is discussed for an extreme flood event of August 2005 in the Chiene catchment, Switzerland, which mobilized 120,000 m³ of bedload along the mountain stream. The simulation results underline the importance of form resistance when modelling bedload transport in steep and rough channels.