Feasibility study for Urrutiénéa dam removal

Preparatory works included a topographical survey, fish populations assessment and hydromorphological measurements of the site, detailing the impacts of the removal of the dam and the measures that needed to limit these impacts.

Introduction

Nivelle River is a 45km long cross-border coastal river. The first 12 km upstream flows into Spain. The next 33 km are in France, including the river’s mouth into the Atlantic Ocean. This river supports a variety of migratory fish, including two species of shad, sea lamprey, European eel, Atlantic salmon and sea trout. The number of salmon that swim up the river each year has fallen from an average of over 200 fish from 1990-2000 to 100 fish (in some years less than 50) in the last 20 years. This species is in sharp decline and particularly threatened in this basin. The causes of the decline are multiple, as in other rivers (habitat quality, water quality, dams, professional fishing, etc.).

This river is also home to the last population of freshwater pearl mussels in the Pyrenees, which live in symbiosis with salmon and trout. It is also in great danger of extinction, and great efforts have been made in recent years to save this population. The upstream part of the river is home to other rare and endangered species, such as the Pyrenean Desman (a small aquatic mammal endemic to the Pyrenees) and the White-clawed Crayfish. Currently, the upstream sector of the river has the best conservation status and spawning grounds for salmon and trout. This section of the river is inaccessible due to the Urrutienea Dam.

At a glance

LocationAinhoa
CountryFrance
RiverNivelle
Potential km to be opened10
Key habitatsSpawning habitat for salmonids
Focal speciesSalmon, brown trout, European eel, freshwater pearl mussel
Project typeDam removal (pre-demolition)
Project statusComplete

Project context and opportunity

Several fish-passes have been built on the two main dams in the downstream part of the Nivelle, but the Urrutienea Dam was never equipped, despite the very high stakes for biodiversity. The owner was always opposed to the construction of a fish pass. For this reason, the project team bought the dam, with the aim of removing it when they became the owners.

This project also had the support of the Government of Navarra in Spain, as it would allow the return of salmon to the Spanish section of the Nivelle. In the context of climate change, the circulation of fish (and of all aquatic organisms in general) is becoming an increasing issue.

This project was very important locally, and it required in-depth preliminary technical studies.

Project aims

The project team performed topographic surveys, estimating the volume of sediment that will be remobilised and drawing technical design documents. During the preparatory phase, the project team defined the measures to limit the impacts during the removal and drew up the specifications and selected the company to present the best skills at the best cost. During this phase, they also drew up the permission procedure.

This project was completed in 2022 and in 2023, the dam will be removed with a follow on grant from the programme.

Project achievements

Thanks to the preparation work conducted, the project’s technical feasibility, the primary goal of the study, has been confirmed. The sediment quality is deemed satisfactory, facilitating natural sediment transit without needing removal from the river. The dam’s influence area has been accurately identified, and the topography and the required resources for the upcoming works are well-defined.

Encountering challenges, the association successfully negotiated with the dam owner, eventually acquiring the dam and associated former fish farm independently of the Open Rivers Programme grant on August 1, 2022. Another hurdle involved opposition from a neighbouring owner, a local authority with ownership of an old mill downstream (refer to the Executive summary). Continuous mediation efforts led to a favourable agreement publicly announced during the last Natura 2000 meeting on September 11, 2022.

A thorough survey of the dam’s concrete quality revealed a combination of reinforced concrete (with embedded iron) and stone components, aiding in sizing the demolition efforts. Additionally, an analysis of potential effects stemming from the dam removal, encompassing both positive and negative aspects on the environment, ecosystem functioning, and fish populations, was conducted.

This project was completed in 2022, and in 2023, the dam was removed with a follow on grant from the programme.

Partners

FEDERATION DE PECHE 64

L’AAPPMA Nivelle

Basque Country Agglomeration Community

Government of Navarre