Significant erosion, transport and deposition of sediment typically occur during medium and large flows in rivers and headwater streams. Measurement of sediment transport under these conditions is challenging, and recent technological developments offer interesting possibilities for new measuring techniques. For ecological and water quality studies, the assessment of contaminant sediment transport is important. Observations and measurements of sediment transport during all flow conditions are essential for developing and testing sediment transport models. The large variety of available sediment transport equations reflects the uncertainty under which conditions these transport equations should be best applied. In mountain streams with a coarse bed and irregular bed-form structures, for example, it is still very difficult to quantify the effects of form resistance and of supply limitation on sediment entrainment and transport. To improve modelling of sediment transport, we need reliable measurements of sediment transport over large ranges of discharges and environmental conditions, and we need suitable modelling approaches taking into account the various influencing factors. For this session we welcome contributions addressing one or several of the above mentioned issues.