The Rhone flows in an EPFL hall!

«Imagine the electricity consumption of 13'500 raclette ovens that work simultaneously»: this is the example, very Valaisan, given by Julien Derivaz to image the power of the future Massongex-Bex-Rhône (MBR) dam. The director of MBR SA and collaborator of the Forces Motrices Valaisannes hopes that the work will be commissioned at the end of 2026. Eventually, the level will produce electricity for 20,000 households, exploiting the flow of the Rhône.

But the road is still long. To build such an infrastructure, we must offer guarantees to the Federal Office of the Environment and the Federal Office of Energy, continues Julien Derivaz. This is why it is necessary to have a physical model, which removes doubts about different phenomena. ' Thus, the contracting authority added the services of the Hydraulic Construction Platform (PL-LCH) of EPFL, to conduct scientific tests.

«Until the Flood»

In a hall of about 700 square meters, the team of the platform, made up mainly of future engineers, built a huge model last summer. Giovanni De Cesare, director of the PL-LCH, describes: All our skills come within the framework of this project. We work on hydroelectricity and dams, we assess design floods for dams and rivers, we verify the safety of hydraulic installations and study the mechanisms of sediment transport in torrents and rivers. '

For such a construction, the requirements are high, he adds, «The bearing must not prevent the transit of sediments, which are an integral part of the river, nor the passage of floating bodies, which must be ensured.» After the optimization of the model at the beginning of 2021, about sixty systematic tests were carried out, allowing to study all the cases of possible loads, from a quiet day in the life of the stream to the millennium flood. “We can even go as far as the flood,” says the director.

Two complementary models

For the physical model, the PL-LCH has a tank of 800'000 litres of water, which gives it the possibility to create an arm of «mini-rhône» in situ. The sediments or floating timber used for the tests are all at the scale of the model. But a digital simulator was also developed by the team of scientists. This allows us to refine our observations and extrapolate further down the river. We take advantage of the strengths of each model,' said Giovanni De Cesare.

The MBR landing will operate 6 to 9 meters of fall. Located in the Rhône, it will play valves to adapt to the conditions of the moment. It is in particular to determine the mode of use of the latter, for the transit of floods or the management of floating litter, that the tests are useful. In case of too high a flow rate, the power-generating unit will be closed and the grids fully raised, in order to allow the water to flow normally, as if no work blocked the passage.

Ongoing discussion with environmentalists

Thanks to the validations obtained, as well as the optimization of the concept after the tests on the models, MBR SA hopes to be able to file its application for permission to build at the end of 2021.

If the Swiss Confederation and the cantons of Valais and Vaud have deemed that the environmental balance is balanced, this is not the case with WWF and Pro Natura, Julien Derivaz, who have appealed in each of the cantons concerned, notes: A participatory approach is being undertaken with these organisations. We are trying to find solutions, which will probably involve ecological compensation. But it takes time.”

According to the director of MBR SA, the project is fully in line with the 2050 energy strategy. He hopes to obtain a financial contribution of 35% from the Confederation, out of a total investment estimated at 158 million francs.