Lescoude Culvert and Gué d’Ahetze Dam, France

Fédération de pêche des Pyrénées-Atlantiques restores longitudinal river connectivity in south-west France

THE RIVER BASINS

The River Bosdapous

River Bosdapous rises at 900 m altitude and runs for 4.5 km before it flows into Gave d’Aspe. The latter is located in south France close to the French-Spanish border (Figure 1). It is inhabited by large populations of Sea trout and Brown trout (Salmo trutta), Atlantic salmon (Salmo salar), and European eel (Anguilla anguilla). The latter two fish species are characterized by the French IUCN red list as “vulnerable” and “critical”, respectively. Atlantic stream crayfish, Austropotamobius pallipes, is also present in Gave d’Aspe and characterized as “vulnerable” by the French IUCN red list. The presence of all these species in River Bosdapous is very limited and restricted to its lowest 0.5 km section due to the presence of Lescoude Culvert. Specifically, only a small number of salmon and trout could surpass the barrier, while eels are completely excluded from the upstream section of the river and could be found only downstream the culvert. However, River Bosdapous has great potential to facilitate the successful reproduction of salmonids, especially Sea trout.

Figure 1. (left) Location of Gave d’Aspe indicated by the orange rectangle. (right) Gave d’Aspe and location of Lescoude Culvert (indicated by the red pin) at River Bosdapous (tributary of Gave d’Aspe)

The River Zirikolatzeko Erreka
River Zirikolatzeko Erreka is a tributary of River Uhabia located in south-west France (Figure 2). It is inhabited, especially in its upper section, by Brown trout, European eel, and Sea lamprey (Petromyzon marinus).

Figure 2. (left) Location of River Zirikolatzeko Erreka indicated by the orange rectangle. (right) Location of Gué d’Ahetze Dam (indicated by the red pin) at River Zirikolatzeko Erreka

BARRIER REMOVAL

Lescoude Culvert
Lescoude Culvert (Figure 3) was located 500 m upstream the confluence of Bosdapous and Gave d’Aspe rivers (latitude: 43.042928; longitude: -0.603469; Figure 1). It was built in the 1990s and used as a river crossing to facilitate car access to a nearby residence. 

Figure 3. Lescoude Culvert at River Bosdapous (photos by Charlie Pichon)

The culvert removal project was run by the Fédération de pêche des Pyrénées-Atlantiques, an organization that aims to protect the aquatic environments and to achieve sustainable development of recreational fishing and has been removing riverine barriers for the last 5 years (Video 1). The removal of the Lescoude Culvert was financially supported by Open Rivers Programme – a grant giving organization dedicated to restoring rivers.  

Video 1. Actions and projects conducted by the Fédération de pêche des Pyrénées-Atlantiques to restore river connectivity

The owner of the Lescoude Culvert was in favor of the removal, as where all the stakeholders involved in this project, including the Town Hall of Sarrance, the “AAPPMA Gaule Aspoise” fishing association and the Syndicat mixte du Gave d’Oloron et Affluents (SMGAO) which is the entity responsible for maintaining the river. The unanimous approval of the removal proposal was imperative to ensure the acceptance of the suggested solution by the local community.

The preparatory work that led to the removal was straightforward, since the structure was not a historical element of the area and thus did not have any heritage value that could prevent its demolition. The authorization for the demolition was acquired in June 2022. Prior to the onset of the removal works, fish were captured through electrofishing and were relocated (Figure 4).

Figure 4. Electrofishing survey and fish relocation prior to the removal works of Lescoude Culvert (photos by Charlie Pichon)  

The removal works initiated soon after (Figure 5) and were completed a few months later, in October 2022 (Figure 6). The culvert was replaced by a bridge to retain the car access to the nearby residence (Figure 7). 

Figure 5. Removal works of the Lescoude Culvert at River Bosdapous in summer of 2022 (photo by Charlie Pichon) 

Figure 6. Removal site after the demolition of Lescoude Culvert at River Bosdapous in October 2022 (photo by Charlie Pichon)

Figure 7. Replacement of Lescoude Culver with a bridge at River Bosdapous in October 2022 (photo by Charlie Pichon)

The final cost of the project (11734.84 €) exceeded the grant awarded by Open Rivers Programme (10930 €) due to an unexpected increase in the prices of supplies that occurred after the authorization of the removal works were obtained. The difference (840.84 €) was covered by the Fédération de pêche des Pyrénées-Atlantiques. This unexpected development led to a delay in the removal works by a few weeks.

Gué d’Ahetze Dam 

Gué d’Ahetze Dam (Figure 8) was the first barrier from the river mouth fragmenting River Zirikolatzeko Erreka (latitude: 43.410022; longitude: -1.567357; Figure 2). It was an old ford made of concrete that has outlived its usefulness and served no purpose any longer.

Figure 8. Gué d’Ahetze Dam at River Zirikolatzeko Erreka (photo by Charlie Pichon) 

This project was run by the Fédération de pêche des Pyrénées-Atlantiques and supported by “AAPPMA Nivelle Côte Basque” fishing association and the owner of the Gué d’Ahetze Dam, a local farmer. The support of the latter two stakeholders was important to prevent any opposition by the local community. The removal of the barrier was financially supported by Open Rivers Programme.  

Authorization to proceed with the demolition works was obtained on July 8, 2022, and removal works started soon after (Figure 9). The barrier removal was completed in October 2022 (Figure 10). The total cost of the project was 2010 euro, slightly less than estimated (2050 euro). The cost of each phase/task of the project is presented in Table 1.  

Table 1. Cost (in euro) per phase/task of the Gué d’Ahetze Dam removal project 

Figure 9. Removal works of the Gué d’Ahetze Dam at River Zirikolatzeko Erreka in summer of 2022 (photo by Cédric Nanini) 

Figure 10. Removal site after the demolition of Gué d’Ahetze Dam at River Zirikolatzeko Erreka in (up) October 2022 and (down) February 2023 (photos by Charlie Pichon) 

ECOLOGICAL AND COMMUNITY BENEFITS

Lescoude Culvert

River Bosdapous is now fully reconnected with Gave d’Aspe. The removal opened more than 4 km upstream. Eels are expected to colonize and salmonid fishes to take advantage of the newly opened sections of the river for spawning purposes. Monitoring surveys will be carried out following the removal to record whether fish populations take advantage of the newly opened river sections upstream the removal site.

This project could be a case study and pave the way for the removal of more culverts that are numerous in the area. The preparatory work and the removal process could be replicated and used for similar projects. Also, a local construction company was trained on the demolition processes during this project and this technical know-how could be used in next culvert removals.

Gué d’Ahetze Dam

The removal of Gué d’Ahetze Dam opened 3 km upstream and will enable unrestricted fish migration at all hydrological conditions. The first barrier currently fragmenting River Zirikolatzeko Erreka is a culvert located 3 km upstream from the removal site and opposes a partial barrier for fish migration.

DISSEMINATION OF NEWS

The news of the Lescoude Culvert and Gué d’Ahetze Dam demolitions were disseminated through the social media and website of the Fédération de pêche des Pyrénées-Atlantiques. The news was also presented in two daily newspapers, including “Sud-Ouest”, a daily newspaper with a wide readership (200000 copies on a daily basis) (Figure 11).

Figure 11. The news of the Lescoude Culvert and the Gué d’Ahetze Dam demolitions on the printed version of “Sud-Ouest” newspaper 

BEFORE & AFTER PHOTO PAIR

Lescoude Culvert

The removal site at River Perkalaba: (left) before and (right) after the removal operations of Bayurivka Dam (photos by Yaroslav Zelenchuck) 

Gué d’Ahetze Dam

The removal site at River Zirikolatzeko Erreka: (left) before and (right) after the removal operations of the Gué d’Ahetze Dam (photos by Charlie Pichon) 

Written by Foivos A. Mouchlianitis