New hydraulic gallery to improve operation conditions at the Emosson hydro scheme

A new hydraulic gallery was constructed to increase operational resilience and mitigate risks of Emosson hydropower scheme in the Swiss-French Alps. One of the main constraints of the operation is to avoid the overflow of the so called "Corbes" surge chimney during pumping, if the upstream valve is closed. While this scenario is very rare and happened only three times since the commissioning of the dam in 1973, it is considered as a critical issue for operation of the scheme due to the high risk of this event. Different solutions have been studied to avoid the overflow of the surge chimney. However, the safest solution was to create a new gallery bringing water from the top of the surge chimney to the Emosson Reservoir. However, the execution of the new so-called "Corbes" Gallery took place in challenging alpine conditions with difficult access and a very tight schedule.