Preparing to remove the Molino de Arquijas dam in River Ega, Navarra, Spain

Preparatory works to remove a second dam on the upper Ega River to recover fish access to high-quality spawning areas located upstream, thus increasing their reproductive success and conservation status.

Introduction

Molino de Arquijas Dam is located in a Nature Reserve and Natura 2000 site in the Ega River basin, a tributary of the Ebro River, in Spain. This unused dam is the uppermost dam in the Ega River and represents a major obstacle to the migration of potadromous fish that are considered Key Elements for the management of the “Ega-Urederra Rivers” Natura 2000 SCI (ES2200024), Parachondrostoma miegii and Achondrostoma arcasii, both included in Annex II of the Habitats Directive.

The removal of this dam is linked to the Molino de Gastiain Dam removal, also promoted by CIREF and funded by the Open Rivers Programme, the second uppermost dam of the Ega River located 4.9Km downstream and in the same Natura 2000 site, for which the technical project of the demolition is already drafted. The holistic approach proposed by CIREF, removing both dams, will free 44,7 Km of the upper Ega River from obstacles and help meet the conservation objectives proposed for this Natura 2000 site.

The ecological status of the fish species that inhabit the upper reaches of the river Ega will be improved when the two dams are removed. These dams prevent fish migrations to the upper reaches, which is of great importance to ensure the survival of eggs and juveniles of these species. Spawning in lower reaches increases the probability of mortality caused by floods, higher water temperatures and predation. Hence, the strategy of the targeted fish species is to migrate upstream to areas where their offspring have a better chance of survival. Genetic exchange between individuals along the river, colonization of new territories and increased food availability are other reasons why migration is important for these species and the improvement of their conservation status.

At a glance

CountrySpain
RiverEga
Km to be opened34.8
Key speciesParachondrostoma miegii and Achondrostoma arcasii
Project websitehttps://cirefluvial.com/en/programa-open-rivers/
Project typeDam removal (pre-demolition)
Project statusComplete

Project context and opportunity

The mills built in the Ega River were used for centuries to grind the cereal produced in the area. However, with the modernization of the agricultural sector, the mills became obsolete and little by little, they were abandoned. Only the remains of the old buildings and the dams used to divert the water remain standing. Both dams are in poor condition, which poses a danger to crops, goods and people located downstream since their rupture could cause serious damage.

Removing both dams will facilitate the achievement of the objectives of several plans and regulations adopted for the Ega basin. The Management Plan of the Natura 2000 SCI proposes to “improve the habitat conditions of the native fish community”; the Master Plan for the Ebro River Basin contemplates the elimination of the dams that are out of use to meet the objectives of the WFD; the National River Restoration Strategy also proposes the elimination of disused dams and, finally, the European Biodiversity Strategy, which aims to reach 25,000 km of rivers free of obstacles.

But the main reason to remove the dams is to recover the access of fish to high-quality spawning areas located upstream, thus increasing the reproductive success and conservation status of important fish species such as Ebro nase and Red gurnard, two freshwater fish species from the carps family, endemic of the Iberian Peninsula.

According to the latest Habitats Directive article 17 report, the conservation status of the two target species is ‘unfavourable-inadequate’ and deteriorating in the Mediterranean region. The main pressures described for both species are human-induced changes in hydraulic conditions (canalization and dams) and alien species. Therefore, it is time to begin eliminating those infrastructures that interrupt fluvial continuity and recover the natural dynamics of the river.

Project aims

The proposed holistic approach will free the uppermost 45 km of the Ega River, allowing genetic exchange and access to spawning areas for two fish species included in Annex II of the Habitats Directive and declared Key Elements for the conservation of this Natura 2000 SCI in its Management Plan. An information campaign addressed to stakeholders, and a monitoring scheme to establish the baseline for future longer-term monitoring are also foreseen.

Regarding the social benefits, the area is frequented by hikers and fishermen who will see how the natural environment will benefit from removing the dam, as river habitats will diversify. The dam removal’s positive impact on native fish species will benefit brown trout anglers. By releasing the water withheld upstream of the dam, the quality of the flowing water will improve, especially concerning oxygenation and self-purification capacity so that the water intakes located downstream will also be benefited. The demolition of the dams would avoid potential catastrophes that could occur if the dams broke in a flood.

This project has many possibilities of being replicated in other places since, in the Iberian Peninsula, there are hundreds of similar cases. CIREF will make a great effort to publicize the results so that the project can be replicated, to improve fluvial governance working together with other regional and water authorities.

Project achievements

The main objective of the project was to draw up the demolition project and all the technical documents that will enable the structure to be completely demolished in the future, managing the impact to adapt the riverbank vegetation and accelerate the naturalisation process.

The demolition project of the Arquijas dam and the preliminary studies have been completed. Over a period of eleven months (January to November 2023) work has been carried out on the following points:

  • Technical project and preliminary studies for the demolition of the dam
  • Public participation sessions in the area to publicise the Open Rivers Programme and the project to demolish the Arquijas dam to neighbours and stakeholders.
  • Creation of audiovisual material on the benefits of dam removal and the before and after of other dams removed in the region.
  • Technical project management, coordination, administration, and communication with Open Rivers.

View programme-supported demolition project.

Partners

CIREF