The Basque Water Agency-URA has carried out an intervention on a section of the Mañaria River, as it passes through the Arbizolea industrial estate in Izurtza. The objective of this action was the removal of two disused weirs, thereby re-establishing the river's longitudinal continuity and restoring the free movement of fish and sediments.
The Mañaria River is home to various species, including the loina, Graells' barbel, trout, piscardo or ezkailu, and locha. Furthermore, this river section is part of the headwaters of the Ibaizabal River and is considered an Area of Special Interest for the conservation of the European mink in Bizkaia. Therefore, the aim is to restore the river's continuity, facilitate the movement of fish fauna, and return a more natural sediment transport dynamic to the riverbed.
The two weirs constituted transverse obstacles in the riverbed. The upstream weir measured 12 meters in length and 1.5 meters in height, while the second reached 15 meters in length and 1.5 meters in height. A significant portion of these structures has now been removed, retaining only certain lateral sections that act as deflectors (elements that partially divert the current and influence the river's transport and sedimentation) and protect existing elements on the banks.
The removal of disused transverse obstacles allows for the recovery of a basic characteristic of a functional river: its longitudinal continuity. In this case, the removal of the weirs once again facilitates the displacement of fish species and allows previously retained sediments to be transported downstream by the current itself until a new equilibrium situation is reached.
Where a transverse infrastructure has lost its function, its removal can restore space and continuity to the river and promote the recovery of its natural processes. In Izurtza, the intervention allows the Mañaria River to flow through this section with fewer obstacles and a configuration closer to that of the natural riverbed.
