Enabling the removal of the Henares Weir to benefit nature and people, Spain

Introduction

The Henares Weir, built in 1863 to supply water for irrigating the fields of Mejorada del Campo, is the largest weir on the Henares River. Located within a protected Regional Park, a Special Area of Conservation, a Special Protection Area, and a Madrid Region protected wetland, this steep weir is now obsolete, with both the barrier and the channel in very poor condition.

Removing the 4-metre-high weir would restore connectivity to around 35 km of the Henares River, improving its natural dynamics and boosting biodiversity within a Natura 2000 area. Furthermore, it would enhance the river’s natural dynamics – something rare in rivers within the Madrid Region – which could reduce the area affected by future floods.

Project context and opportunity

The weir’s proximity to Madrid means that several million people stand to benefit from increased conservation value, enhanced recreational opportunities, and greater potential for environmental education. Removing the weir will also strengthen ongoing efforts to eliminate other obsolete barriers along the river.

The removal of the Henares Weir has a high probability of success due to strong partnerships with key stakeholders, including the Environment Councillor of Mejorada del Campo and her team, who are committed to improving the local environment; the Water Authority of the Tajo River Basin; and the Regional Government of Madrid, which oversees protected area management. These partners support the removal and have taken significant steps to facilitate it by (1) listing the weir in the Water Authority’s catalogue of obstacles slated for demolition, and (2) refraining from renewing its expired irrigation concession.

Project aims

Through the development of a weir removal plan, the project has the following (main) objectives:

• Increasing river connectivity, which will undoubtedly boost biodiversity. Removing the weir will also help to reduce flooding and contribute to restoring the river’s natural functions and key ecosystem services, such as water purification.
• Establishing the technical specifications necessary for the weir’s removal and the restoration of this stretch of the river, while considering other conservation and restoration activities in the area.
• Contributing to the improvement of the river’s ecological status. This includes enhancing both the water’s ecological quality and the conservation status of aquatic habitats and species.

Project achievements

Significant progress has been made towards the demolition of the Henares Weir, with the following key achievements:

Engineering and technical preparations:

• All the necessary work for the project design of the demolition of the weir have been carried out by an engineering company, including field measurements and data collection for drafting the technical demolition project.
• A full technical plan to remove the weir and restore this area of the river has been produced taking into account other conservation and restoration activities in the area including a a road map for implementation of the weir removal. The purpose is to model the expected future hydromorphological situation once the obstacle is demolished, both downstream and upstream. The results of the simulation will allow the correct calculation and sizing of the bioengineering techniques used to stabilise the new topography (post-operational situation) with novel calculation methodologies that incorporate the processes of wood deterioration and the reinforcement effects of vegetation.
• An Environmental Impact Assessment report including a specific report, as the weir lies within a N2000 site, has been realised.

Engagement and advocacy

• A participatory workshop with local stakeholders was conducted after the summer of 2024 to foster community involvement.
• Meetings with local NGOs and environmental groups have taken place to align on restoration goals for the Henares River and nearby Jarama River sections.
• WWF was active at the Iberian Congress of Rivers Restoration (Toledo, Spain), organised by CIREF, in the sessions related to dam removal and rivers.
• WWF engaged the Madrid WWF volunteers group, which has been actively involved in seasonal biodiversity monitoring in the Natura 2000 area. This group could play an important role in implementing the monitoring protocol in the second phase of the demolition of the weir.

Coordination with key stakeholders

• Collaboration with the Mejorada del Campo City Council has ensured alignment with territorial objectives and recreational plans for the area.
• Support for the project has been obtained from the environmental NGOs of the nearby municipalities and the Administration of the Southeast Regional Park and Mejorada del Campo City Council.
• The Tagus Water Authority has confirmed that the weir can be legally removed as its concession has expired. Under Spanish national legislation, dam and weir owners are required to demolish their infrastructure at their own expense when it is no longer in use. This measure is enforced as a matter of public safety to prevent abandoned infrastructure from remaining in the public domain.
• A meeting was held with the new Environmental Councillor of Mejorada del Campo and representatives of the Madrid regional government and the Spanish Ministry of Agriculture. The latter has committed both the budget and responsibility for the weir’s demolition.
• WWF has shared all studies and project documentation with the Centro Nacional de Tecnología de Regadíos (CENTER), which will oversee the demolition, implemented by Tragsatec. WWF will play a pivotal role in catalysing the demolition by facilitating the process.

Future impact

• The project will significantly improve the hydromorphological status of the water body, boosting biodiversity, restoring natural ecosystem functions, and enhancing key services such as water purification.
• Increased river connectivity will support flood mitigation efforts and provide opportunities for ecological restoration.