The Pyrenees, Spain-France

In the Pyrenees as well as other European mountains, studies have indicated that landslides and subsequent flooding have decreased in places where forest has conquered past grasslands, especially in the highest part of pastures. In some cases, reforestation has demonstrated its usefulness to cope with hydro-climatic extreme events by reducing the hazard intensity.

However, this positive impact is very local and more importantly it does not include the broader implications of socio-economic impact of land abandonment and downsizing of pastures. Demonstration and monitoring of reforestation in relevant environments is needed to understand the implications of tree species, drainage systems, and agro-pastoral practices.

The Consortium Pyrenees Working Community (CTP) is reaching out to local communities in these vulnerable natural areas to engage them in meaningful dialogue to co-design strategies, funding schemes, monitoring systems, services and policies related to various NBSs. Proposed demonstrations will be realized in collaboration with planned work of municipalities and project proposals that receive funding from the Operational Program for Territorial Cooperation Spain-France (POCTEFA) program for 2014-2020. This program focuses on “Promoting the protection, development and sustainable use of local resources” and “Promoting adaptation to climate change and risk prevention and management.” One of the goals is to propose land use changes as a tool for stabilizing the entire river basin and valleys, with the support of local communities.

Photos from Bareges in the Pyrenees after the flood in June 2013

Proposed and approved NBS interventions

Rock fall and erosion at St. Elena, Spain

At this site, landslides and rockfall from a steep, 25 m high slope consisting of loose glacial till, threaten an important road between France and Spain, the A-136. There is often fallen rocks and debris on the road, and the visibility lof the cars coming from both directions is low due to the curves, whereas the speed is often high. This location has been identified as a high-risk spot on this road. Increased heavy rain episodes may increase the hazard.

The measures to be implemented consists of reshaping the slope trhough terracing techniques, with the establishment of vegetation to stabilize the sediments, together with a drainage system to prevent water to erode and reduce stability of the slope. The terracing will be done using wooden gabions or drywalls, both to ensure a balanced, stable slope profile, and to make the measure as less impacting as possible. In addition, only locally adapted plants will be used.

The practical implementation of the measures is underway, and the tendering process for the works to be carried out is soon to start.

The measures to be implemented at St. Elena are expected to provide several co-benefits:

  • Less frequent need for maintenance and repair, probably leading to reduced costs over time;
  • Increased sense of safety for users of the road, particularly regarding transport of goods between the two countries;
  • Aesthetic benefits, and combining the measure with the system of foot-paths in the area.

Location of the NBS sites at St. Elena, Spain, and Artouste, France, both defined as high-risk locations along the important trans-national road A-136 / RD-934. The proposed NBS intervention at Socques, also along the same road, was cancelled.

The till slope at St. Elena. Loose blocks often hit the road, and small landslides often occur during heavy rain, exposing more blocks to threaten the road.

Rock fall at Artouste, France

At this site, the road, RD-934, bends around sharp hairpin turns below a steep, forested slope. The slope has several steep ledges, where rockfall are released. The forest has a breaking effect on smaller blocks, but rocks often hit the road. In 2013, a fatal accident occurred when a passing car was hit by a falling rock.

The rock fall area at Artouste (right) and a detail from the slope (left).

The proposed measures consist of wooden structures designed to prevent release of rocks, and to stop released rocks before they reach too high velocity. The structures are to be constructed as close as possible to the potential release areas and immediately below. Only logs from the region will be used, and the measures are to be combined with preservation and proper maintenance of the existing forest.

As for other NBS, the interventions at Artouste are expected to provide several co-benefits, in addition to the risk reduction:

  • A large upscaling potential;
  • Economic gain, through less need for repair of the road, and the less need for maintenance compared to traditional engineered measures;
  • Local jobs with construction of the measures, with more to come regarding potential for upscaling;
  • Reduced fear among the users of the road, and more secure transport of goods and people, also important for the tourist industry of the area.

Left: Part of the exposed road. Falling rocks come from the slope above the road cut, and hit the road with high energy.
Right:  Example showing wood constructions similar to those proposed for the Artouste site.

Snow avalanches at Capet Forest, village of Barèges, France

The village of Barèges, an important tourist destination, has been hit by snow avalanches, from the mountain side to the north of the village, several times. The village, which is part of the Grand Tourmalet ski destination and has warm health baths, was evacuated because of avalanche hazard as late as in 2013 and 2015. There are several avalanche paths in the valley side, and a number of existing measures exist, in the form of fences and barriers. These do function, but in extreme winters the existing fences are buried in snow, and avalanches can be released from the snow pack above the fences. This was the situation during the last avalanche that reached the village. In addition, they require extensive maintenance, which mostly have to be carried out on foot, and is therefore very labourious.

The NBS intervention currently being implemented consists of afforestation in the release area of Midaou, one of the known avalanche paths, with the plants being protected by tripods of wood until they are 4-5m high and can stabilize the snow pack. Until then, the tripods will also have some stabilizing effect on the snow. The plants are carefully selected and are adapted to the region and the altitude. They are also meant to withstand prognosed climate change, are robust and will not need extensive maintenance.

The implementation of the measures started in the summer of 2020 and was more than 50% completed before the work had to be closed down for the winter. The work will be completed as soon as the conditions allow the work to proceed in the spring of 2021.

The NBS interventions at the Capet Forest have several co-benefits:

  • Less costly maintenance operations; less human pressure and probably economic savings;
  • Environmental benefits through less need for helicopters to lift heavy material for maintenance. This is also of benefit for wildlife in the forest. It also helps preserve several of the species and biotopes in this high elevation forest;
  • Increased sense of safety amon the villagers, both regarding the village itself, but also regarding road closures, etc.
  • Less avalanche threat is important for the tourism in the area, which is important (alpine skiing, health baths, etc.);
  • Huge upscaling potential, if successful.

The Bastan Valley, with Barèges in the red circle. The cancelled NBS projects in the Bastan Valley were planned downstream from Barèges, and in the city of Luc.St-Saveur.

Left:  The release area of snow avalanche path Midaou where the afforrestaion is taking place (red circle).
Right:  Construction of the wooden tripods between the existing structures.

Proposed but cancelled NBS interventions

Two proposed and approved NBS interventions have been cancelled for various reasons. At Socques, also along the transnational road A-136 / RD934, torrents cause frequent problems.
A set of wooden barriers was proposed, to form a step-pool profile of the stream and thereby reduce the erosional energy. However, this measure was called off due to doubts regarding its effeiency.

Two flood controlling measures in the Bastan Valley, France were cancelled due to an expected lengthy processing time until implementation would be possible, and fear that this would not be possible within the project period.

 

Debris flow measures at Erill-La-Vall, Spain

The village of Erill-la-Vall in the Spanish Pyrenees is heavily affected by debris flow problems, where sediments are fed from tributary creeks and into a main debris flow channel leading to the village. The source area consists of thick deposits of glacial till. The measures to be implemented here consist of a combination of revegetation, to limit erosion, and constructions of logs from local wood to minimize energy in the creeks, all to reduce the feeding of sediments to the main debris flow channel.

The proposed NBS interventions are currently under evaluation by the project’s Steering Committee, and implementation is planned to start already in 2021. Co-benefits expected from the interventions comprise:

  • Improved sense of safety among the population
  • Less need for costly maintenance
  • Positive effect on the terrestrial plant ecology of the area
  • Positive effect on tourism in the area, i.e. an economic co-benefit.

Left: Thick till deposits and active erosion feeds debris to the main debris flow channels.
Right: Overview of the problematic area. The village is below the figure.

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See PHUSICOS Case study site poster PYRENEES at Kick-off.

Contact person: Idoia Arauzo,  i.arauzo@ctp.org