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Argos Reservoir

Territorial framework.

Geology and Geotechnics.

Regional geology and geotechnics

The Argos reservoir is located in the northernmost part of the Baetic System which, in turn, represents the north-western segment of the Peri-mediterranean Alpine Orogen (alignment of mountain chains with asymmetric topologies created during the Cretaceous and Tertiary eras, centrifugally arranged relative to the sea; Martín Algarra, 1987).

In the Baetic System, the area of interest is delimited within the External Areas or South Iberian Domain. The materials in this area occupy a vast extension in the mountain range and represent a time period which goes from the Triassic to the Miocene. Its structure is characterized by a general detachment between the base rock (Hercynian Paleozoic) and the deformed covering (Mesozoic and Cenozoic folds, faults and buckled strata), where the clayish-evaporitic Triassic level acts as the detachment material and the buckled strata are generally inclined towards the W and NW. The Paleozoic base does not surface, remaining at a depth of 5-8 km, and it is made up of materials analogous to the Iberian Massif.

According to the nature of the materials and strain rate, it is possible to clearly distinguish two areas:

  • Pre-Baetic, with facies located in shallow areas which represented the nearest area to the continent during the Mesozoic, formed by the Iberian Massif.
  • Sub-Baetic, with pelagic facies from the middle Liassic which represent the most distant marine area from the continent with materials from the oceanic basin and, possibly, volcanic effusive rocks during the Mesozoic.

Between them, it is possible to observe the Intermediate Units in some areas of the continental slope with generally turbitidic facies linked to the deposit in submarine flares and which could locally reach a relevant width. They have their own features with important lateral differences from the Pre-Baetic and the Sub-Baetic.

Furthermore, it is possible to distinguish the autochthonous materials of our area of study, corresponding to the post-orogenic formations which were deposited there after the allochthonous units were placed, representing the Quaternary layer.

Photo of the Argos reservoir

Basin geology and geotechnics

The basin is made up of Triassic clays, apart from a small section located on the left abutment, exactly to the left of the structure above the Argos-Quípar Channel, where slightly sandy marls and marly limestones from the Lower Cretaceous emerge.

The basin slopes are quiet soft and stable, so there should not be significant disturbances due to the natural operation of the reservoir.

Geology and geotechnics of the enclosure

Geologically, the enclosure area is mainly characterized by alternate layers of limestone and marl, which are more or less calcareous. On the left abutment, the limestone and marl (Lower Cretaceous) drop (about 15º) towards the riverbed.

On the right margin, which is a hard escarpment (part of the Cabezo de Teruel peak), it is possible to observe limestone and dolomites alternating with grayish-black marly layers which turn ochre on the surface due to weathering. Such limestone and dolomites (Upper Cretaceous) are more fractured and split than those on the right margin over which they ride.

Before this over-thrust, another took place in which Triassic clay were thrust on the Cretaceous marl limestone; later on, favored by this more fluid layer which acted as a lubricant, the limestone and dolomites that make up the Cabezo de Teruel thrusted over the remaining series.

Thus we have, between the two marly-limestoney formations, a multicolor clay coat deeply nestled on the other side of the peak, which extends towards the watercourse, although it is covered by debris for the entire segment of the river occupied by the dam, and it appears at the bottom of the right margin escarpment upstream and downstream from the site.

Due to such an anomaly (the presence of the clayey coat and Triassic gypsum under the Teruel peak), a plug was built on the entire front side of the impermeable core of the dam, after excavating the altered rock at the bottom of the peak escarpment, with subsequent injection and, in addition, a battery of injections so that they vertically reached under the Triassic layer, and traversed the peak horizontally until it closes the Triassic trace East of it, thus guaranteeing the dam's impermeability and stability.

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The seismic hazard is different from one place to another, and it has been common practice to classify areas according to this hazard. Taking into account the recommendation criteria included in the “Dam Safety Technical Guidelines. Geological and Material Prospecting Studies” published by the Spanish National Committee on Large Dams (SNCLD), paragraph 3.3, there are three large groups:

  • Low seismicity areas. Coefficient ab < 0.04 g
  • Medium seismicity areas. 0.04 g < ab < 0.13g.
  • High seismicity areas. 0.13 g < ab

(ab is the standard acceleration of the area.)

Photo of the Argos reservoir

According to this classification, the Argos reservoir is located in an area of medium seismicity, given that the standard acceleration for the Calasparra Municipality is 0.07 g (data from the Seismic Resistance Regulation NCSE-02).

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Environmental information.

The Argos reservoir is located in a SPA (Special Bird Protection Area) known as “Sierra del Molino, Embalse del Quípar y Llanos del Cagitán” code ES0000265, established by resolution on May 8, 2001. Furthermore, because it is a SPA area, the dam is included at the same time in the Wildlife Protection Area known as Alfonso XIII, Cagitán y Almadenes Reservoir.

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