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New solution to potable water supply on La Gomera PDF Print E-mail
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Sunday, 10 May 2009 16:04

The Hydrological Plan of La Gomera is an example of how an island can satisfy its demand for potable water in a sustainable manner and with the greatest respect for the environment. On no other island in this archipelago the premises of sustainability and respect have been achieved in such a clear and effective manner as on La Gomera. The key to this success has been determined by a clear and total commitment to groundwater reserves.

The island of La Gomera began searching potable water in the surface runoff of its numerous gullies. This hydraulic policy resulted in the construction of thirty large dams such as La Encantadora, Amalahuigue, Los Chejelipes, Mulagua, etc. These large waterworks yielded one of the highest dam densities in the world, but owing to the torrential, sporadic and meager nature of surface runoff, they only managed to give a percentage of the water flow required by the island.

At the beginning of the 1990's the water situation on La Gomera was particularly dramatic. The municipal nuclei, landlocked generally on the coast and demanding most of the urban supply, suffered from the scarcity and low quality of the water obtained from saline wells, such as those of San Sebastián and Valle Gran Rey. Hamlets on higher grounds such as Chipude, Erques, Igualero and so many others, which had always been supplied with water from the springs, had at that time a flow rate that barely covered their meager needs and this began to cause problems of public order. And for its part, agriculture and the demand for irrigation water in boroughs like Hermigua was not better either.

In this tense and dramatic situation a new Hydrological Plan of La Gomera was introduced, which proposed a drastic change in the island's hydrological policy: to abandon the water catchment in the gullies in favor of drillings made into the groundwater reserves. This new approach was proved viable already in the first drilling surveys on areas with most severe shortage of supply. The rapid acquisition of water soon showed that the change in policy towards the abstraction of groundwater was cheaper, faster and had less impact on the insular landscape.

The surveys that were conducted in Enchereda, Benchijigua, Erques, Las Palomas, etc. demonstrated that in the subsoil of La Gomera there's water of excellent quality in sufficient quantity, and these drillings were used to supply all the population centers, giving an end to the dramatic situation and the problems between municipalities. Concurrently an Insular Hydrological Plan (IHP) was developed, which as a first step defined a zone of reserve, one that feeds the headwaters of the island and where drilling should never be conducted, so that the number and flow of water from the natural springs of the Garajonay National Park would remain unchanged.

In about a decade, following the guidelines of IHP, the necessary groundwater was found and networks of pipes were built that today continue to supply all the nuclei of La Gomera. Thus two major transfers capture and supply the water in the south of the island, and once the needs there are met, they transport the surplus to the center and north of the island. One transfer passes through the massif of Enchereda supplying San Sebastián, Hermigua and Agulo, and the other, catching the groundwater in the gullies of Erques and Guarimiar, leads it to Alajeró, Vallehermoso and Valle Gran Rey. On La Gomera it has been shown that the premise "water is extracted from where available and taken to where needed" is as simple as effective.

At present and financed by the Ministry of Environment, two galleries are being drilled in order to replace the surveys as a cheaper and safer method of satisfying the potable water needs. Of these two the gallery of Ipalán, located in Barranco Seco, is being drilled to give water to the eastern half of the island. After one year and having drilled 1.700 meters in dry, the aquifer has just been reached, obtaining water that has one of the highest qualities in the Canaries.

As indicated by the analysis, the mineralization is weak with a dry residue of 224 mg/l, and having a calcium and magnesium content of soft water. Thus, according to the Royal Decree 1074/2002, the water can be classified as natural mineral water. Therefore we can say that the future water supply of the eastern half of La Gomera will be done with water having quality similar to the bottled one, a luxury that very few places in the world can afford. Moreover, the excellent quality of the water gained from the gallery has made the Cabildo Insular to plan a bottling plant, taking advantage of not only the quality but also the location of the gallery.

Owing to the technique of closures in the volcanic dikes drilled by the gallery, only the amount of water which is needed at each moment is extracted from the gallery, and the rest is being used to replenish the aquifer. Three major benefits are thereby achieved: the waste of water posed by the open galleries is avoided, as well as the need for regulating reservoirs like those on Tenerife; the aquifer can be used to act as a reservoir, extracting and replenishing as needed; and finally, thanks to the veritable swarm of dikes in the aquifers, raising of the water level is achieved, making it possible to extract the water flow on levels higher than the mouth of the gallery.

Like the other Canary Islands, La Gomera began looking for water in the gullies, but unlike Tenerife and La Palma, abandoned forever that solution for being too random and dependent on annual rainfall. Moreover, the island differed from Gran Canaria, El Hierro, Tenerife, Lanzarote and Fuerteventura as well, by refusing desalination of sea water, since it did not want its water supply to depend on the precarious existence and the abusive price of crude oil.

The result is clear to see - La Gomera has settled the demand for water indefinitely, with a quality equal to that of bottled water, and with a natural solution based on capture of underground water, using a technology that the Canaries know as nobody else has come to know in this world. Now La Gomera could become an example to be followed, not only in this archipelago but also in any other of the endless archipelagos which are scattered all over the oceans of this world.

La Gomera has solved its potable water supply with an economic, ecologic and sustainable solution for always. Can anyone else say the same?

Submitted by Julián Horcajada and Carlos Soler - Hydrological Plan of La Gomera