“30 years ago, 99% of the water consumed in Tenerife was underground and today it is less than 75%”

“30 years ago, 99% of the water consumed in Tenerife was underground and today it is less than 75%.” This was expressed by the technical engineer of Public Works and hydrologist, Juan José Braojos Ruiz, who opened the Cues conference cycletion of Balance. Water in Tenerife, Tradition and Avant-gardea, organized by the Bethencourt y Molina Canarian Cultural Foundation of Engineering and Architecture, in collaboration with the Royal Economic Society of Friends of the Country of Tenerife (RSEAPT).

During his dissertation, he explained that rain, together with snow, and the so-called horizontal rain form the beginning of the integral water cycle and constitute the basis of “traditional” conventional water resources: surface and groundwater. According to him, the total average annual rainfall that Tenerife received between 1944/45 and 2014/15 was 958 cubic hectometres, of which326 recharge the basal aquifer, where the large reserve of water from which the island has been supplied is housed.

The engineer highlighted that the availability of traditional conventional resources is “absolutely linked” to the extraction of groundwater through wells and galleries, where they are stored according to the three types of structure that characterize it: impermeable vertical walls (“interdykes”), on layer (where the water does not encounter obstacles and flows towards the sea) and the Las Cañadas aquifer, divided into two large “buckets”.

A review of the history

Tenerife’s water availability in the mid-19th century was provided by some coastal wells and those in the Vega de La Laguna, but with very low flows. It was the natural springs that offered the greatest amount of water. The phreatic surface was then very close to the surface of the land and in the ravines with large jumps, springs with very important flows were produced. At this point, he remembered that back then they talked about the rivers of Tenerife, such as in Aguamansa, in Güímar, in Adeje, and some ravines in Anaga, Arico, Granadilla…

By then, The water availability of the island was about 22 cubic hectometers per year, but there were great territorial imbalances, since the northern slope had 80% of the production, compared to 20% in the south. Furthermore, more than 50% of the resources generated on the northern slope were concentrated in the La Orotava Valley. On the other hand, the scarcity of pipelines and the precariousness of the existing ones meant that utilization did not even reach 50%.

Braojos explained that in 1840, when the Santa Cruz laundries were being planned, the scarcity of water led to the birth of the first gallery on the island. The City Council proposed to increase the flow of the Aguirre springs using an auger to drill “artesian wells” brought from England; but the first experiments did not give results and it was some individuals who, with prior permission from the council, put the drill in the hands of a French subject who knew how to use it and, as a result, the first horizontal subsoil drilling in Tenerife arose in search of water: the nascent gallery La Cueva del Francés. Only 10 or 20 pipes were lit, but it was the starting point for more drilling and the creation of societies and companies for research, exploitation, channeling and use of groundwater.

In 1915, there were already 300 galleries on the island, most of them small spring galleries, which provided a combined flow of 23 hm3/year which, together with lighting from wells and springs, made up an availability of 33 hm3/year; That is, in 75 years and with 50 kilometers of subsoil drilled, it only increased by 11 hm3/year. However, he did highlight the evolution during the 19th century of the channeling of water from the areas in which it was extracted to those of consumption, since it was possible to increase the use of availability to over 80%.

Twentieth century

The engineer highlighted that, at the beginning of the 20th century, the lack of water in Santa Cruz led the City Council to a new project: transferring water from the Roque Negro springs, in northern Anaga, to Los Catalanes, in southern Anaga, through the execution of a tunnel. In 1912, 613 meters from the south mouth, more than 1,500 pipes/hour emerged behind a dam (unfortunately, five workers lost their lives in the event); had contacted the basal aquifer.

Years later the conventional gallery Los Huecos in Arafo would do it. Thus began the exploitation, through galleries, of the great aquifer.

After the Spanish Civil War, he explained, the exploration of the subsoil in search of water intensified, giving rise to new and abundant floods that made the availability of water almost equivalent on both sides and in 1950 it grew up to 160 hm3/year and up to 255 hm3/year in 1965, its historical ceiling. Starting in 1950, groundwater extraction exceeded rainfall recharge.

The lowering of the water ceiling left the highest galleries hanging above and dry. The flows from the new lighting did not compensate for those lost in the galleries that were being exhausted; Consequently, the unstoppable decline in the production of gallery water began and with it the island’s water availability, which had to be sustained with the entry into the scene of boreholes. Later, at the end of the eighties, the Tenerife Balsas Plan put into service more than 20 hm3/year of gallery water that was thrown into the ravine channels in the rainy months. Around that time, the private sector once again contributed to recovering the lost flows by increasing water extraction from wells and implementing the first seawater desalination plants on the island (several hotels in the south, Cepsa, Unelco).

“Without remedy, the public sector also had to resort to unconventional resources. In 1993, with regenerated water (WWTP) and, in 1996, with desalinated seawater (EDAM); initiative supported by the private sector. Of the 44 existing desalination plants, 40 are private and 4 public,” he added.

The hydrologist concluded that, although conventional resources will continue to decline, especially those illuminated by galleries, groundwater could continue to account for half of the island’s water supply in the future. “We will always count on groundwater,” he stressed.

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