Molino Del Cabrillas Weir and Molino Bajo Weir, Spain

The removal of these two weirs helped to restore ecological continuity, natural flows of water, sediments and nutrients, and fish farming connectivity.

Introduction

The scope of action is the lower and middle course of the Cabrillas River, within a high-value protected area, the backbone of the Tagus River, which, together with its headwater tributaries, has carved out a set of the most important karstic gorges and canyons in Spain. Due to its geographical isolation, low population density, absence of large urban centres and lack of industrial activity, the area has preserved a great environmental value, recognised as a Natural Park two decades ago.

With more than 1,000 km2, the Alto Tajo is the largest protected area in Spain and is included in the Natura 2000 Network. It includes a great diversity of habitats, river courses, hillside forests, karstic gorges, rocky outcrops and moors, all with great diversity of flora and fauna species of great ecological value, including 20% of the flora species present in the Iberian Peninsula, and numerous protected birds and mammals.

In turn, the wide fluvial space of the Alto Tajo encompasses more than 240 km of main river up to the first regulation reservoir. Species of high conservation value live in these cold-water rivers, such as the crayfish (Austrapotamobius pallipes) or native fish, most of which are endemic to Iberia and protected by European and Spanish legislation, such as Squalius pyrenaicus, Luciobarbus bocagei , Squalius alburnoides, Pseudochondrostoma polylepis and Achondrostoma arcasii. The dominant fishing species is an indigenous salmonid, the brown trout. This species has a population here with a recognised genetic singularity. Due to its reproductive migratory behaviour, it will also be one of the most benefited from the barrier removals. Other valuable species associated with the river, which will be highly favoured by the recovery of fluvial connectivity, are the kingfisher, the dipper, the Iberian desman, the vole water and the European otter.

At a glance

Project typeDam removal: demolition
Project statusComplete
Removal DateNovember/December 2022
CountrySpain
RiverCabrillas
Km to be opened25 in the Cabrillas River, 50 adding the section of the Tagus River
Key habitatsCalcareous Mediterranean mountain rivers and surrounding forests
Focal speciesSqualius pyrenaicus, Luciobarbus bocagei, Squalius alburnoides, Pseudochondrostoma polylepis, Achondrostoma arcasii, Salmo trutta, Alcedo atthis, Cinclus cinclus, Galemys pyrenaicus, Arvicola sapidus and Lutra lutra
WebsiteRios con Vida

Project context and opportunity

The actions will contribute significantly to the objective of the European Biodiversity Strategy of 25,000 km of barrier-free rivers.

Removing the dams is expected to positively impact the river ecosystem, helping to restore ecological continuity, restoring natural flows of water, sediments and nutrients, and fish farming connectivity. The removals will especially benefit the aquatic species, particularly the fish species present, the majority with reproductive migratory behaviour. The ecological reconnection with the Tagus is even more important considering the tendency towards the compaction of its substrate, which produces a certain scarcity of adequate spawning areas for fish, which the Cabrillas, however, do have. Concerning the brown trout, the removal of the weirs will allow the spawning area to be increased by more than 25 km of habitat that is more suitable for migrant spawners from the Tagus, and will reduce the fragmentation of the trout population of the Cabrillas itself, favouring the exchange and genetic variability and contributing to the strengthening and resilience of reconnected populations.

The removals will help to improve and consolidate the ecological status, with a particularly positive impact on the fish populations, benefiting recreational fishing and ecotourism.

Project aims

The elimination of the two barriers restored ecological continuity to the last 25 km of the Cabrillas River up to its connection with the Tagus River, reestablishing continuity in more than 50% of this body of water in connection with the main axis of the basin. In turn, this fluvial length is also reconnected with the 25 km of the unobstructed section of the Tagus River to which the Cabrillas flows, adding 50 km of barrier-free fluvial courses.

The Molino Bajo Weir removal helped restore the river’s original longitudinal continuity, the associated ecological processes, and the natural landscape to its original state. The Molino del Cabrillas Weir removal helped eliminate the retention and impact due to the barrier effect and returned the original longitudinal continuity to the river and associated ecological processes.

The actions contribute to improving and consolidating the ecological status of the river, with a particularly positive impact on the community of fish and other species linked to the river environment, benefiting recreational fishing and contributing to improving the landscape, tourist and recreational value associated with the use and enjoy the river and its surroundings.

This project is the 2022 Dam Removal Award winner.

Project achievements

Regarding environmental impact, the demolition projects and work plans underwent thorough review and coordination with relevant bodies in the autonomous community responsible for environmental matters and protected natural spaces. Collaborative efforts aimed to select appropriate alternatives and methods, ensuring a reasonable impact assessment and optimal environmental harmonisation. Additionally, all necessary authorisations and permits were obtained to execute the actions.

The removal of barriers has successfully restored ecological continuity along the last 25 km of the Cabrillas River, reconnecting it to the Tagus River. This initiative aimed to enhance the ecological status of the water body by reinstating natural water flows, sediment and nutrient movements, and fish farming connectivity. The positive impact on fish fauna has been a notable outcome. The proposed actions have also improved the landscape, tourism, and recreational value of the river and its surroundings.

The actions have significantly improved the state of the “Río Cabrillas a Río Tajo” water body (ES030MSPF0129010), classified as R-T12, “Mediterranean calcareous mountain rivers,” designated as a “Natural River” and “Permanent,” covering a total length of 59 km. This has reestablished continuity in over 42% of the mass connected to the Tagus River.

To see the complete project report click here (only available in Spanish).

Partners

AEMS

Gobierno de Espana

Castilla-La Mancha

Alto Tajo