NBS implemented in the Pyrenees during the PHUSICOS project

The H2020 project PHUSICOS designs and implements NBS for DRR at demonstrator case sites in rural areas of Norway, Italy, and in the French and Spanish Pyrenees. This presentation covers four locations in the Pyrenees, where NBS to reduce risk from snow avalanches, rockfall and debris flows are implemented. Snow avalanches from the steep slopes of the Capet Forest threaten the French village of Barèges. The NBS here consist of afforestation in the release areas. 5000 trees have been planted in groups of 30-50, protected behind wooden tripods, which also act as protection structures until the trees are large enough to stabilize the snowpack. Rockfall poses a severe hazard at two locations along the important road A-136 / RD-934 between France and Spain. At St. Elena, Spain, the rocks are released by erosion of a slope in a thick till deposit. The implemented NBS consists of vegetated terraces, built up by a dry masonry wall and gabions constructed from wood and filled with the local till. At the location in Artouste, France, rockfalls in the steep slope are released from exposed ledges and from loose blocks in the till surface. The measures here consist of wooden stabilising and retaining structures for each individual ledge or block. These solutions are also tested at newly established laboratory and full-scale test facilities in Spain and France, respectively. The fourth location is near the Spanish village Erill-la-Vall, where debris flows from a >50m thick till deposit pose the threat. Several gullies feed the main debris flow path towards the village during periods of extreme precipitation. The implemented solution is a series of terraces, built up by local rocks and whole-log gabions in the lower parts of the gullies. These will prevent deepening of the erosional base and form increased rugosity in the debris flow paths. The site has been monitored during the last 15 years. In-situ borehole (piezometer) data shows two processes: a deep-seated (15-20 m) failure level, which reacts up to two weeks after a period of heavy rain, and shallow erosion, which reacts almost immediately as a direct response to heavy precipitation. The implemented NBS are primarily to mitigate against the latter process.

The NBS described here all have large upscaling potential, as there are numerous locations in the Pyrenees and elsewhere with similar problems. Terracing and afforestation for slope stabilization is not a new concept but is here re-vitalized in cooperation with stakeholders through Living-Lab processes. These processes have also helped overcoming challenges related to land ownership issues and permissions to operate, e.g., in national parks, which have caused implementation delays. Monitoring of the implemented measures, focused on both the resilience aspect and, not the least, the NBS' co-benefits will be important for building up an evidence-base for the functionality of NBS for DRR.