The Basque Water Agency-URA, under the Department of Industry, Energy Transition and Sustainability of the Basque Government, has commenced the partial and progressive demolition of the Mendizabal dam. This structure is situated on the Ibaizabal river, beneath the Montón bridge (Montoiko zubia), on the border between the municipalities of Iurreta and Durango.
The objective of this action is to enhance the river's hydraulic performance during floods and simultaneously restore its fluvial continuity. The weir, built around 1860 and currently disused, acts as a transversal obstacle that disrupts the natural flow regime, hinders sediment transport and the movement of fish populations, and causes water levels to rise excessively during floods.
This intervention will make approximately two kilometers of the Ibaizabal permeable, covering the stretch shared by Iurreta and Durango. It will also contribute to reducing the flood risk in the Significant Potential Flood Risk Area (ARPSI) of Iurreta. The project is part of the measures outlined in the Flood Risk Management Plan 2022-2027 and aligns with URA's commitments under the collaboration agreement signed with the Iurreta City Council on November 2, 2023.
The dam measures approximately 28 meters in length, about two meters in width, and 1.5 meters in height from the riverbed. Given its characteristics, age, and location under the bridge, a progressive demolition approach has been adopted, involving the creation of openings (breaches) in the dam's structure.
The work is being carried out by creating dry enclosures using big-bags, which contain the water flow and allow for dry demolition of the dam. This ensures that at least one span remains open for water circulation at all times.
The execution of both phases has a combined budget of 141,191.22 euros, including VAT. The first phase is expected to take six weeks, and the second phase will take five weeks.
In addition to reducing flood risk, the intervention will progressively restore more natural conditions to this section of the Ibaizabal. The removal of the obstacle will promote fluvial connectivity, species migration, natural sediment dynamics, and the recovery of the habitat's physical characteristics.
