As part of the Undúrraga Dam project, a 1,300-meter bypass tunnel has been built from the tail-end of the reservoir to the foot of the dam through the rocky massif on the left side of the reservoir, with two 900 mm diameter PRFV pipes embedded in the floor of the tunnel. At the tail-end of the reservoir a diversion dam and an intake have also been constructed, through which water is diverted to the bypass tunnel and to the Venta Alta DWTP. At the exit of the tunnel, a discharge has been built at the foot of the dam to reduce water flow.
Objectives of the project
- To improve the hydrological safety of the Undúrraga dam, significantly increasing the structure’s relief capacity – by 64 m3/s for the maximum storage level and to 110 m3/s for the crest elevation – complying with the technical regulation of dam and reservoir security by being able to create laminar flow in cases of extreme flooding (T = 5,000 YEARS – 288 m3/s)
- To guarantee drinking water to the Venta Alta DWTP, directly supplying a 5m3/s flow from the tail-end of the reservoir without using the available reservoir storage volume or the existing intake. This objective responds to the need to ensure supplies to the Metropolitan Area of Bilbao in the event of an emergency or in the case of repair to the Undúrraga dam preventing its functioning.
- To use the bypass tunnel for muddy overflow from the Arratia river in the event of heavy rains that might affect the quality of supply from the Undúrraga Reservoir.
The project, along with other drainage work, achieves a peak flow return period of 1,000 and 5,000 years, as anticipated in Spain’s Comprehensive Flood Prevention Plan, used by the Bilbao-Bizkaia Water Consortium.
Attendees at the event
Representing the Bilbao Bizkaia Water Consortium at the event were Ricardo Barkala, President; Pedro Barreiro, Manager; José María Villanueva, Technical Director and Eduardo Elguezabal, Exploitation Director. On behalf of the Municipality of Zeanuri, where the dam is located, were Mayor Eusebio Larrazabal; while the Basque Water Agency (URA), was represented by Ernesto Martínez, Manager; and on behalf of the Provincial Council of Vizcaya, Deputy Elena Onzueta.
Representing Ferrovial Agroman were Ángel Luis Sánchez, Director of Zone I Construction; Juan Magín Lozano, Director of Civil Works for Spain and Portugal; Alberto Val, Civil Works Manager of the Zone, as well as Project Manager Enrique de las Cuevas, among others.
The construction team, led by Manager Alberto Val, included Enrique de las Cuevas, Construction Manager; José María Rodríguez and Miguel Cavia, Tunnel Specialists; Luis Miguel Blanco, External Works Senior Manager; Ángel Antonio Seco and Aitor Casaña, surveyors; Miguel Ruiz, Tunnel Manager; Jesús del Hierro, Tunnel Foreman; Alberto Blanco, External Works Manager; and Jesús Varela, Administration.