Open Access

C. Auel, R.M. Boes

• Reservoir sedimentation is an increasing problem affecting the majority of reservoirs both in Switzerland and worldwide. As many dams are more than 50 years of age, this problem is becoming more and more serious nowadays. Res-ervoir sedimentation leads to various severe problems such as a decisive de-crease of the active reservoir volume leading to 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. Therefore, countermeasures have to be developed. They can be divided into the three main categories sediment yield reduction, sediment routing and sediment removal. This paper focuses on the sediment routing using sediment bypass tunnels. Sediment bypass tunnels are an effective means to decrease the reservoir sedimentation process. By routing the sediments around the reservoir into the tailwater, sediment accumulation is reduced significantly. However, the number of sediment bypass tunnels in the world is limited primarily due to high investment and maintenance costs. The main problem of all bypass tunnels is the invert abrasion due to high velocities in combination with high sediment transport. Three Swiss bypass tunnel examples suffering invert abrasion are presented in this paper. Furthermore, VAW started a research project to investigate the invert abrasion process by conducting hydraulic scale tests in the laboratory. The goal of this research project is to establish general design criteria for optimal flow con-ditions where both sediment depositions in the tunnel are avoided and the result-ing abrasion damages are kept at a minimum.