June 9, 2021

Vidange du Rhône 2021

A few weeks ago, the Vidange du Rhône (or Chasses du Rhône, meaning Flushing of the Rhône) took place between Barrage de Génissiat (Genissiat Dam) in France and Barrage de Verbois (Verbois Dam) in Geneva. Both the CNR (Compagnie Nationale du Rhône), which manage the dams on the French side, and the SIG (Services Industriels de Genève) cooperate on this operation: It is performed every few years in order to purge sediments brought into the Rhône river by the Arve, which accumulate and increase the risk of floods.

For a few days, the dams in the area are opened and their reservoirs emptied, in order to increase the discharge rate with the goal of flushing the sediments from the river bed. The river then turns gray, just like the Arve. Another side effect is that the level of the Rhône is lowered, almost as low as before dams were built along the river so it becomes quite the view. One other, less happy, consequence is that it is a bit of a fish apocalypse, with many of them dying because of the increase in solids suspended in the water.

I went to see this phenomenon in the area around Bellegarde-sur-Valserine, first in Éloise near Pont de Grésin, as part of a hike. Then a few days later, I visited Bellegarde itself just for this purpose and walked along the Rhône. Because of the the Corona restrictions on border crossings, unfortunately, I couldn’t visit the area upstream of the Verbois Dam in Geneva.

On this page, there is a download link to an interesting Powerpoint (PPS) with many pictures from the Vidange in 2012 in the area near Bellegarde. Here are photos of the 2012 Vidange from the area near the Verbois dam.

The photo at the top of this post was taken in in Bellegarde-sur-Valserine near the confluence of the Valserine river with the Rhône. There used to be an hydro power plant on the platform (Forces motrices de Coupy), which went underwater when the Génissiat Dam was built in the 1940’s. In the background, is the location of the Pertes du Rhône (similar to the Pertes de la Valserine nearby). It remains underwater.

▲ The same location in normal conditions.

▲ Pont de Lucey, next to the Pertes de Rhône.

▲ In normal conditions.

▲ Valserine river, just before the confluence.

▲ Waters mixing at the confluence. It looks like the Jonction of the Rhône and Arve in Geneva, except that this time, the Rhône is the gray one.

▲ Valserine canyon upstream towards Pont de Coupy.

▲ In normal conditions.

▲ The rock that is normally underwater is covered with small mussels.

▲ Valserine river at Pont de Coupy.

▲ Upstream of Pont de Coupy. The former Usine électrique Louis Dumont is just after the bend.

▲Downstream of Pont de Coupy.

▲ Remains of the Forces motrices de Coupy.

▲ Nicer in normal conditions.

▲ “Le Rhône et la Valserine”, by Milos Jiranek.

▲ Platform of the Forces motrices de Coupy.

▲ Remains of Usine électrique d’Éloise (an hydro powerplant).

▲ Rhône see from Pont de Savoie, with Viaduc de Bellegarde on the right.

▲ A waterfall has formed.

▲ Sediments normally underwater.

▲ After crossing Pont de Savoie to Éloise, I walked a small path going down to the bank on the left side of the Rhône.

▲ A few days before, I had visited Pont de Grésin in Éloise, upstream of Bellegarde.

▲ Upstream, towards Le Vuache.

▲ Downstream.

▲ I walked on the riverbed below Pont de Grésin. It is supposed to be dangerous so it is not recommended to get on the submerged part but it was a gentle slope on that side.