Design and construction of the sediment bypass tunnel at Solis

Since the construction of the Swiss Solis reservoir in 1986, high sediment input from upstream mountain torrents has led to major aggradations, already filling nearly half of the original reservoir volume. A sediment bypass tunnel is under construction to flush the incoming bedload around the dam to the tailwater in the future. The tunnel intake design and the approach flow were hydraulically optimized based on model tests at the Laboratory of Hydraulics, Hydrology and Glaciology of ETH Zurich. The tunnel will begin operation early next year. An overview of the hydraulic model tests and the construction process is presented.