CH Matxategi Dam, River Deba, Basque Country, Spain

CH Matxategi Dam removal within the framework of the River Deba basin restoration project

The River Deba
River Deba (Basque: Deba ibaia; Spanish: río Deva) is located in the Basque Country in Spain. It springs in Arlaban and flows into the Atlantic Ocean, in the Bay of Biscay, in Gipuzkoa Province (Figure 1). The Deba basin covers a large (534 km²) and highly populated area with ~135000 people live within it and includes different types of habitats, like urban, peri-urban and agricultural. In the south, River Deba borders with the ZEC Arno Natura 2000 site (Figure 1). Similarly, many of Deba’s tributaries spring from the ZEC Izarraitz and ZEC Aizkorri Aratz Natura 2000 sites and have been characterized as sites of natural interest (Figure 1). More specifically, they are registered as protected areas, sections of special interest in connectivity, areas of special interest for the Pyrenean desman (Galemys pyrenaicus), a small semiaquatic mammal related to moles and shrews, or for the European mink (Mustela lutreola). The latter is characterized by the IUCN (International Union for Conservation of Nature’s) Red List of Threatened Species as critically endangered, while the former as threatened.

Figure 1. The River Deba basin in the Basque Country, Spain. Natura 2000 sites, areas of special interest and the location of barriers are shown. The location of CH Matxategi Dam is indicated by the red rectangle

River Deba was heavily polluted and fish numbers were extremely low during the second half of the 20^th century. Industrial waste from urban areas was the main source of pollution. In the 21^st century, the water quality was significantly improved (Figure 2) due to the implementation of proper waste treatment measures, which led to a significant improvement of biological quality as well (Figure 3).

Figure 2. Annual measurements of physicochemical quality in CH Matxategi Dam (River Deba)

Figure 3. Annual measurement of biological quality (IBMWP index) downstream of Bergara (River Deba)

Despite the improvement in water and biological quality, longitudinal river fragmentation remains a serious issue for the whole Deba basin (Figure 4). Dozens of barriers, most of which remain obsolete, occur throughout the basin, impeding fish migration, altering natural habitats and increasing the risk of flooding. Fish species richness shows evident decline from the river mouth (A. Ab. Mendaro) towards its sources (Epelet) (Figure 5). In particular, the population density of catadromous fish, such as the European eel (Anguilla anguilla), has been decreased significantly from sea to source (Figure 6).

Figure 4. Fragmentation of the River Deba basin in the Basque Country, Spain, due to riverine barriers. The location of CH Matxategi Dam is indicated by the red rectangle

Figure 5. Fish species richness in River Deba from the river mouth (A. Ab. Mendaro) towards its sources (Epelet). The relative location from river mouth of CH Matxategi Dam is also shown

Figure 6. Density of the European eel Anguilla anguilla in River Deba from the river mouth (A. Ab. Mendaro) towards its sources (Epelet). The relative location from river mouth of CH Matxategi Dam is also shown

The CH Matxiategi Dam
The CH Matxiategi Dam was located in the center of the Deba basin (Figures 1 & 4; latitude: 43.11281925, longitude: -2.41639098) and in the center of Bergara city (Figure 7). It was an ~1-m-high and 32-m-long stone dam (Figure 8). It was built to accommodate the needs for water of the Goienetxe (or Guenetxe) mill. The Goenetxe mill and its relative house were first mentioned in 1576 when Catalina de Maella / Ms Gaviria, and Isabela García de Amézqueta leased the property to María de Elorza and Marina de Eguren. In 1891 the City Council of Bergara requested authorization for a change of use in the flour mill to power street lights. In 1894, owners of the mill were the owners of the Bergara, Echaide y Cia cotton thread and fabric factory. In 1929, S.A. Algodonera de Asan Antonio applied to be registered in the Registry of use of public waters, so they could use the dam for power generation purposes. The property was partially demolished in 1982 for the construction of the new Bergara GI-627 bridge.

Figure 7. Location of the CH Matxiategi Dam at River Deba, Gipuzkoa Province, Basque Country, Spain (photos by Gipuzkoa Provincial Council)

Figure 8. The CH Matxiategi Dam at River Deba, Gipuzkoa Province, Basque Country, Spain (photo by Gipuzkoa Provincial Council)

Dam removal
The removal process of the CH Matxiategi Dam was initiated in 2022 and executed by the Gipuzkoa Provincial Council. It was part of the River Deba basin restoration project. The removal works (Figures 9-10; Videos 1-2) lasted 1.5 month, costed 50.000€ and were financially supported by the EU Horizon 2020 project MERLIN (Mainstreaming Ecological Restoration of freshwater-related ecosystems in a Landscape context: INnovation, upscaling and transformation). The general aim of the MERLIN project is to implement transformative ecosystem restoration and to mainstream nature-based solutions.

Figure 9. Demolition works of the CH Matxiategi Dam at River Deba, Gipuzkoa Province, Basque Country, Spain (photos by Gipuzkoa Provincial Council)

Video 1. Demolition works of the CH Matxiategi Dam at River Deba (video by Gipuzkoa Provincial Council)

Figure 10. Removal site after the demolition of the CH Matxiategi Dam at River Deba, Gipuzkoa Province, Basque Country, Spain (photo by Gipuzkoa Provincial Council)

The location of the dam, in the city center, was considered by the project managers the perfect opportunity to showcase the importance of the project and also to shift the perspective of the local community towards dam removal practices. At the beginning of the project, concerns and objections were expressed by the local community. There was a lack of understanding regarding the necessity of the dam removal. Before the initiation of the project, local authorities (the mayor of Bergara and council members), stakeholders, schools, canoeing groups and nature associations were invited to discussions aiming to explain the steps of the restoration actions, the significance of the project and the expected socio-ecological benefits. The involvement of the locals in the project helped the project managers to understand their point of view and to promote the restorative actions more efficiently. Through this project, stakeholder interaction has been promoted, as has the connection with local communities, institutions and governments. Among the stakeholders involved in the removal of the CH Matxategi Dam were municipal councils, the Basque Country Water Agency (URA), the Society for the Economic Development of Deba Basin (DEBEGESA), the Deba Basin Rural Development Association (DEBEMEN), the Commonwealth of the Upper Deba and the Eibarko Baso Biziak.

Video 2. Removal of the CH Matxiategi Dam at River Deba (video by Gipuzkoa Provincial Council)

Ecological and community benefits
The River Deba basin restoration project aims through hydro-geomorphological restoration – including barrier removals – to reduce the risk of flooding, mitigate the environment degradation, enhance the biodiversity, restrain climate change, and improve human health. Comprehensive monitoring of the water quality, the invertebrate and fish communities, as well as of the whole ecosystem function followed the dam removal, using a BACI (Before-After-Control-Impact) design.

Before & After photo pairs

The removal site at River Deba: (left) before and (right) after the removal operations of CH Matxiategi Dam (photos by Gipuzkoa Provincial Council)

With many thanks to Gipuzkoa Provincial for providing the information and the visuals presented herein.

Written by Foivos A. Mouchlianitis