Environmental Engineering Reference
In-Depth Information
Figure 1.
Dike across lava flows.
Figure 2. sectional view a water gallery on the hierro
island, canary islands, spain.
The other type of aquifer, most exploited, mainly
because the population centers and land uses are
established near the sea, is called the coastal aqui-
fer, this presents an important difference that, it is
affected by the tides, so we have a fresh water body,
which “floats” by its density above the body of salt
water, denser, the border between the two phases,
is a fragile mix zone (interface). The latter aquifer
is more exploited than the first and here is where
mainly the effects of seawater intrusion. There
aren't dikes in this part of the aquifer.
flows to 200 l/s, representing about 6 hm 3 per
year.
The function of a gallery is twofold since, besides
acting as water collector, also serves as a transport
medium for this. The galleries are perforated usu-
ally by explosives because of the hardness of the
basalt.
as discussed, a fundamental concept for under-
standing the aquifer exploitation by horizontal gal-
leries located at considerable heights above sea, is
that, the aquifer is raised by dikes. Dikes are cells
where the water is stored; these dikes create a stag-
gering basaltic aquifer with dynamic hydraulic gra-
dients. The highest concentrations of dykes are set
at the ridges of the islands. These ridges are higher
rainfall areas of the islands, with vertical rainfall
and convective rain, they are the areas where the
aquifer is higher.
The galleries have a singular constructive sys-
tem, are basically oriented toward the ridges of
the islands, based on what was said previously,
is not possible to apply continental areas drilling
techniques, such as tunnel boring machines drill-
ing machines, because mainly to the following
issues: the first is a gallery of water has no outlet
and the other reason is that volcanic material is
very heterogeneous, that creates many problems in
tunnel boring machines drilling, in case a problem
of calibration of force may even rupture, since in
the front can be anything from a layer of slag or
basalt.
The choice of construction method to be used in
any underground works will be conditioned, first,
by the geotechnical characteristics of the land to
drilling and secondly, by the geometry and size of
the excavation.
it is possible to estimate the properties of the ter-
rain and geological materials by studing technical
literature works and projects in similar perforations.
1.4 Water mining
The horizontal galleries for obtaining underground
water is a method widely millennium. From ancient
times was known as far away as china, Persia,
spain and latin america.
The canary archipelago gets much of its water
resources primarily from underground water, mainly
in the Western isles our case study, in the eastern
islands, by the water scarcity, little rain, erosion and
evapotranspiration, eastern islands are mainly sup-
plied by desalination of water sea, in fact the first
desalination plant was installed in lanzarote in the
60s, although as has been found there in the last cen-
tury in the archipelago of Malta and more recently
in the twentieth century in Gibraltar and Turkey
were the first desalinations plants in europa.
in the late nineteenth century began piercing
galleries in those parts where it was clearer evi-
dence of the existence of groundwater, ie, in areas
already existing natural springs.
The horizontal gallery type, most common, has
a small section of 1.80 by 1.80 m, mainly were built
by private initiative, although built by the admin-
istration have come to section 4 and 2.50 m, with
a length of up to 6 km, where water are obtained
by gravity. These horizontal galleries are oriented
towards dorsals. Generally have produced water
 
 
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