Micro hydroelectric power stations in mountain streams

Chaire Paysage et énergie (ENSP), 2022

To download : brochure-petite-hydro-2018-planches.compressed.pdf (4.7 MiB)

Micro hydroelectric power stations in the Hautes-Alpes, energy from mountain rivers

1 - The Serre-Ponçon lake and its valleys, water and electricity

The village of Crévoux is part of the landscape unit of the Serre-Ponçon lake valleys. This artificial lake, located in the Durance valley, is the major part of this unit, extending over 20 km. The dam was built in 1960 to produce hydraulic electricity. The huge mountain lake resulting from the dam quickly became a tourist attraction: swimming, water sports and leisure activities, campsites, hotels and restaurants, etc. The exploitation of the dam lake, subject to energy needs and climatic hazards, leads to seasonal tidal phenomena which significantly affect the perceived and experienced landscape. These transformations are at the origin of banks in perpetual mutation. Well-marked valleys cling perpendicularly to the lake, notably that of Crévoux, which benefits from the tourist dynamic linked to the presence of Serre-Ponçon. The dialogue with the lake takes place through balcony views.

2 - Crévoux, a mountain commune

Crévoux is a mountain commune located in the Parpaillon massif. The Crévoux torrent flows into the Durance at the foot of Embrun. There is a strong contrast between the right bank, a rocky wall that is mostly bare, and the left bank, a wooded slope dominated by larches. The valley is steep and has few services, except for mountain tourist activities, with a ski resort and numerous hiking trails. Small-scale agriculture is present, with cattle for meat and goats for milk and its transformation into cheese. Today, the population of the village is decreasing, with little renewal. The proximity of Embrun, twenty minutes away by car, is both an asset and a hindrance, giving some people the desire to live in the countryside, and at the same time generating a dormitory village.

3 - The Guil and Queyras valleys, the iconic mountain

The village of Cervières is part of the landscape unit of the Guil and Queyras valleys. It is associated with strong representations, in particular that of an iconic mountain with deep valleys, ridges at over 3,000 metres, mountain pastures grazed by herds and small villages. The reputation of Queyras and the Guil valleys is based on its history marked by religious conflicts, its traditional livestock and craft activities, and its preserved landscapes.

4 - The village of Cervières, a remarkable site

The mountains that surround the village of Cervières strongly frame the views. The commune has created and maintains Nordic ski trails. These trails are part of the « Nordic Alpes du Sud ». The west-east exposure of the valley gives the different mountain slopes marked characteristics. On the sunniest slopes there are meadows, while on the other side the mineral character of the mountain predominates, with numerous screes. Small terraced fields are located at the exit of the village. Their typology is interesting; they are open, without fences, and their shape follows the unevenness of the terrain.

From the RD 902 coming from Briançon, the arrival on Cervières is wide and open. The buildings are grouped together on a grassy plateau and form a clearly identifiable terraced silhouette. Off-centre elements such as the church of Saint-Michel (listed as a historic monument) are very visible in relation to the village core.

The two mountain streams of Crévoux and Cerveyrette have a similar layout, with mountain villages of the same size and operating with the same economy of small-scale agriculture and tourism. They both support micro-hydro power projects that benefit the attached communes.

Energy projects adapted to the needs of the villages

1 - The power station projects, joint reflections between the town halls and the companies

The Crévoux torrent has already been in operation with a micro-hydro power station since the survey of the installations carried out in 1989, in the commune of Saint-André-d’Embrun. The project for a second power station emerged in the 1990s, but the file was initially rejected by the Prefecture and the Department. In 2013, SERHY Ingénierie contacted the mayor of Crévoux to propose the development of a micro-power station project above the existing Saint-André-d’Embrun facility. To this end, the two parties signed an agreement describing, in particular, a redistribution of annual royalties representing an amount of approximately €60,000. The town hall accepts the renewal of the old power station and the project for a new power station in 2013. Ségolène Royal’s call for projects for « Positive Energy Territories for Green Growth » in 2015 offers financial and institutional support for the project. The company SERHY Ingénierie is specialised in small hydroelectricity. Initial feasibility studies were initiated in 2013. Then a file was launched at the DDT, under the authority of the Prefecture. The impact study file was built up over six months; it was initially rejected because it was very incomplete and insufficient on the environmental and technical aspects. The company reworked these aspects, particularly ecological and landscape aspects, and the file was accepted six months later. It took four years to draw up and examine the environmental authorisation file and thus obtain the prefectoral decree allowing the construction and operation of the hydroelectric scheme.

« The examination of the file by the investigating department takes about 6 months following the simplification of the investigation procedure. This is a relatively short period of time to study all the documents in the file. We therefore attach great importance to getting closer to the administration’s coordinating services during the pre-investigation phase so that they can familiarise themselves with the project that we will submit to them during the investigation. Nathan Ranc, SERHY Ingénierie

The work will start in October 2018 and the recoiling will take place in December 2019. However, the winter period during which work is impossible must be deducted.

« As soon as the prefectoral decree is obtained, we will begin the procedures for the construction of the development. In Crévoux, we managed to put the facility into service in 1 year and 4 months… » Nathan Ranc

In Cervières, on the Cerveyrette torrent, two power stations already exist. They are operated by the Société d’économie mixte (SEM) Énergie Développement Services du Briançonnais (EDSB), which will also build and operate the new power station, with a specific economic model. The municipality owns the entire land area of the EDC plant, and only part of one of the existing plants. A feasibility study was launched in 2012.

In 2015, the application file for the water right of authorisation, which includes, among other things, the « Étude d’impact », is examined by the prefecture, and the authorisation for the operation of the Cerveyrette by the new power plant is granted, leading to the start of the works in 2016. An important point in the impact study file concerns the architectural aspect of the plant building. Indeed, the micro-power station is located opposite the church of Saint-Michel, which is classified as a historical monument.

In 2017, the first turbine tests were carried out and in spring 2018 the final fittings completed the construction. Production was launched in January 2018.

For this project, the SEM Énergie Développement Cervières (EDC) was created. The municipality has the means to contribute to the project, the shares are shared between EDSB (49.9%) and the municipality of Cervières (50.1%) so that the latter has the majority. The EDSB company is already an SEM. This semi-public company, created in 1990, is 49% owned by the commune of Briançon. It replaced the Régie Electrique du Briançonnais created in 1924.

2 - Qualitative contributions for the communes

During the construction period of the Crévoux power station, the SERHY company employed people from the village. The power station brings in a financial windfall of 60,000 euros per year for the commune. At the start of the works, the town hall asked the company to add a drinking water network. The network of the penstock passes under some agricultural land; this allows the farmers to benefit from the company’s contributions (excavations or embankments required, removal of piles of stones, etc.). These elements put together provide real added value for the commune. For the Cervières plant, the board of directors meets four times a year. It is composed of 5 members, 3 representatives of the majority shareholder, i.e. the commune, and 2 representatives of the EDSB company. The power station brings economic added value to the village, and the penstock passing close to certain gardens allows irrigation work to be carried out. In addition, a hiking trail is being renovated during the construction period.

Landscape and architectural aspects of the micro power stations

The Crévoux and Cervières power stations consist of a water intake, a buried penstock and a plant for the micro power station. In both cases, the landscape studies were carried out by an environmental consultancy, which also produced other chapters of the impact study file (fauna and flora, hydrobiology, etc).

1 - Crévoux - Run-of-river developments

The water intake of the Crévoux power station is located 4 km upstream of the micro power station. It is located near the commune’s cross-country ski resort. It is hidden behind a rocky hill and can only be seen from a bridge a few dozen metres upstream. The intake building is not plastered; the concrete is left rough to match the rocks. The dam opens with a flap valve, which allows the materials to be evacuated from the basin; the latter is never obstructed. A fish pass is built for fish species. A fish pass of this type is essential, especially for the upstream migration of trout. A little further downstream, the underground penstock passes between the Crévoux torrent and the departmental road. The work has resulted in a semi-concreted stone riprap of the site, with a submerged part. The riprap can only be seen if you walk along the banks very close to the river; it almost gives the impression of a dry stone wall. A little further on, the penstock passes under terraced farmland. The soil was reseeded and enriched after the work was completed. The land is well reworked. Part of the cleared site is replanted with naturally occurring species. This choice raises questions about the closure of the agricultural landscape and the advance of coniferous forests.

The building of the micro-power station is hidden from the road behind an embankment. It is located on the edge of the river, just opposite a beautiful waterfall. The building was designed directly by the SERHY company, then signed by architects for validation. With its roughcast, decorative wood cladding, its volume and its surroundings, it stands out in this remarkable site. Calling in an architect from the beginning to the end of the project would have made it possible to obtain a work of quality in the end. The State’s examination of the building permit did not trigger any particular quality requirements. The DDT requested the construction of a low retaining wall on the edge of the bank to protect the site from potential flooding, without any quality of integration into the landscape. As the project is not on a listed site or in the vicinity of a historic monument, the opinion of the ABF is a ‘simple’ opinion. There is no regulatory obligation that applies, enforceable against the petitioner.

2 - Networks and local dynamics

The electrical production is connected to an Enedis substation in Saint-André-d’Embrun; it is then reinjected locally in Crévoux and the surrounding villages. The procedure for connecting to the Enedis network is complex, as it can only start once the prefectural decree has been obtained. The working time between the SERHY company and Enedis is therefore very short. As far as land is concerned, the project was complicated to set up. For the file to be complete, it is necessary to have the authorisation of all the owners affected by the project area. The Crévoux town hall made a major contribution to obtaining the authorisations, of which there were many.

3 - Cervières - Run-of-river developments

The water intake of the Cervières power station is located 2.5 km upstream of the micro power station. It is quite far from the village, along a hiking trail. It is located in the Cerveyrette notch, in scree areas.

The riprap bed at the level of the water intake is made up of blocks taken from the site. The most important part is a dam wall 1.95 m high over about twenty metres, closing the torrent bed. It is made of concreted blocks of stone from the site; its appearance is a little rough, especially as it can be seen from the front from a small bridge located a few metres away. The accompanying structures are smaller and semi-buried. The walls of the building are left in raw concrete, in order to facilitate their proper integration into the rocks. The volume of the building is itself integrated into the slope. The water reservoir is about fifteen metres long.

The penstock trench was filled in and the surface materials were put back into place. On the paths and the meadow areas, spontaneous vegetation has been reclaimed.

The architecture of the micro power station building is interesting; it was designed by a local architect. He took advantage of the heritage constraints (the nearby presence of the church of Saint-Michel, a listed building) and the « showcase » effect of its location at the entrance to the village. The power station is one of the first buildings to be seen when arriving from the road, and it is visible from almost everywhere in the village and on the surrounding footpaths.

It is north-south facing, with a two-sloped roof and light-coloured rendered walls. The roof is clad in wood. The shape of the rounded window in the façade was chosen to « recall » the stained glass window of the church of Saint Michael overlooking the village.

The factory and the church are indeed in covisibility, although the factory is not within the protection perimeter of this historic monument. The building is also well integrated into the landscape; local trees are planted around the building in a discontinuous manner, as well as soft earthworks. An existing low retaining wall made of stone and concrete blocks is extended over a few metres along the river. It is hardly visible from the road and the power station.

The electricity produced is fed back into the Enedis network.

Long-term benefits of hydroelectric power for mountain villages

1 - Tourism and global warming

The financial contributions generated by the two power stations enable the communes to carry out new projects. For the commune of Crévoux, the desire is to develop a ski resort with a chairlift. « We need tourism, even if the future of winter sports seems to be compromised in the face of global warming » Marie-Jeanne Faure Climate change, even if it is not yet visible locally (particularly on the snow cover), will modify the mountain landscape in the coming decades. The issue of tourism, particularly winter sports, will change. The financial contributions of micro-power stations will therefore have to be diversified. However, they can be used to vary this offer to accompany the change.

2 - The future of micro hydroelectric power stations

The Crévoux and Cervières power station projects have set an example locally, particularly in terms of their integration into the landscape. Numerous communes are contacting the developers to carry out similar projects. The Cervières project won an architecture prize. It is notably cited as an example by the CAUE des Hautes-Alpes.

Sources

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