Reservoir sedimentation is increasingly affecting the majority of reservoirs all over the world, leading to various severe problems such as pronounced decrease of the active reservoir volume. This in turn causes both loss of energy production and water available for water supply and irrigation. These problems will intensify in the near future, because sediment supply tends to increase due to climate change. Sediment bypass tunnels are amongst others an effective countermeasure to decrease or even stop the reservoir sedimentation process. By routing the sediments around the reservoir into the tailwater in case of flood events sediment accumulation of both bed load and suspended load is significantly reduced. Another advantage gaining in importance is the ecological and sustainable aspect of sediment routing. River bed erosion downstream of the dam is stopped and the morphological variability increases. Only sediments provided from the upstream river reach are conveyed through the bypass tunnel, and no removal of already accumulated sediments in the reservoir occurs. However, the number of sediment bypass tunnels in the world is limited primarily due to high investment and above all maintenance costs. Quasi all bypass tunnels in operation are facing an abrasion problem. Due to high flow velocities in combination with high sediment load abrasion of the tunnel invert is significant, leading to major recurring maintenance costs. Having in mind that design of sediment bypass tunnels depends on both the hydraulic and the sedimentologic conditions a suitable layout is difficult. Whereas the basic hydraulic design is easy to determine, a crucial lack of knowledge exists in considering the sediment transport processes in the tunnel. Therefore this research project has been launched to focus on sediment transport in bypass tunnels accounting for the invert abrasion.