Molino de Gastiáin Dam, Spain

One of two dam removals along the upper Ega River to restore fluvial continuity and recover the natural dynamics of the river.

Introduction

Molino de Gastiáin dam is located in a Natura 2000 site in the Ega River, a tributary of the Ebro River, in Spain. This unused dam is the second 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.

This dam’s removal is linked to the Molino de Arquijas dam, the uppermost dam of the Ega River located 4.9 km upstream and in the same Natura 2000 site, for which the technical project of the demolition will be 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 inhabiting the River Ega’s upper reaches will be improved when the two dams are removed. These dams prevent fish migrations to the upper reaches, genetic exchange between individuals along the river, colonization of new territories, and decreased food availability.

At a glance

CountrySpain
RiverEga
Km to be opened9.9
Key habitatsthe natural succession of riffle-pools; fast flowing, shallow and cold waters
Key speciesParachondrostoma miegii and Achondrostoma arcasii
Project websitehttps://cirefluvial.com/en/programa-open-rivers/
Project typeDam removal (demolition)
Project statusLive

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 due to the lack of maintenance after the abandonment of the activity, which poses a danger to crops, goods and people located downstream since its rupture could cause serious damage downstream.

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; and, the Spanish National River Restoration Strategy foresees the removal of out-of-use dams.

But the main reason to remove the dams is to recover the access of fish to high-quality spawning areas located upstream, thus increasing their reproductive success and the 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, which includes the elimination of two dams, 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.

The recovery of the natural river habitats is also an important reason to remove the two dams. The fish habitat upstream of these two dams is inappropriate for the native fish species (adapted to fast-flowing, shallow and cold waters). Instead, the deep, slow-moving and poorly oxygenated waters upstream of the dams offer favourable conditions for alien fish species that proliferate and compete with the native fish, some even predating them. Removing the dams will recover the natural succession of riffle pools, creating an unfavourable habitat for alien species and favouring the increase of the native fish populations.

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. In addition, the positive impact that the demolition of the dams will have 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. With regard to flood prevention, the demolition of the dams would avoid potential catastrophes that could occur if the dams (in poor condition) 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.

Partners

CIREF