AQUIFERS.Since the 1980s, the Basque Energy Agency has studied 6 hydrogeological units in Alava with resources of 325 hectometres at the beginning of the 21st century.
The main one is the Subijana aquifer, which has been studied since 1985. Only 1.5 cubic hectometres of this aquifer are exploited per year, compared to the 72.5 hectometres possible. Its basin covers 170 square kilometres. Its waters were used to alleviate the 1990 drought. The water that gushes out of Nanclares is a turgor, one of the many springs that the technicians call the Subijana Hydrogeological Unit. An immense underground reservoir whose average flow in Nanclares is 440 litres per second of very clear water. This aquifer, an underground sea that extends the subsoil rocks from the east of Vitoria-Gasteiz to the confluence with Burgos, holds reserves of 72.5 cubic hectometres per year, the Urrunaga reservoir at its maximum capacity.
In addition to Subijana, the Ente Vasco de Energía (Basque Energy Agency) counts up to 6 underground reservoirs in Alava with resources of 325 cubic hectometres, twice as much as the network of Zadorra reservoirs. Despite the efforts made by the Provincial Council in recent years as a way of guaranteeing supply to many towns, only 16 % of this resource is used.
After the great drought of 1990, which made it necessary to carry out emergency works to capture this resource, the Greater Bilbao Water Consortium and the Basque Government have their sights set on incorporating the Subijana aquifer into the general network that supplies half of the Basque Autonomous Community-Basque Country. This would make it possible, among other things, to lower the level of the Zadorra reservoirs that put the capital of Alava at risk of flooding every time it rains torrentially.