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Reservoirs

Alfonso XIII Reservoir

Territorial framework

Physical features of the basin.

The surface of the reservoir basin reaches 833.37 km². The elevation of the riverbed in the dam is 261.68 above sea level. The maximum altitude in the basin is 2.081,00 m.

The reservoir surface at the maximum normal level, hereinafter MNL, is 223.26 ha. Its entire surface is within the Region of Murcia. The reservoir volume at such elevation is 13.70 hm³.



Alfonso XIII Reservoir Catchment Basin

Environmental information

No record of any environmental or dam construction impact studies exist, undoubtedly because of the date of execution of the works.

Afterward, the works carried out have generally been small, so that no study of the kind has been required.

In addition, the Alfonso XIII reservoir as such is considered an ICS (Important Community Site), ES6200043 called Río Quípar.

Furthermore, the reservoir is adjacent to another ICS area called Sierras y Vega Alta del Segura y Ríos Alhárabe y Moratalla (código ES6200004).

The reservoir is located inside the SPA (Special Bird Protection Area) area known as “Sierra del Molino, Embalse del Quípar y Llanos del Cagitán” con el código ES0000265, establecida por Resolución de 8 mayo de 2001. Además, por ser una zona ZEPA, el embalse está incluido a su vez en un Área de Protección de la Fauna Silvestre denominada Embalse de Alfonso XIII, Cagitán y Almadenes.

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Geology and seismology

Geology

The general geology of the area is described in:

  • Geological map of Spain. E: 1/50.000 (IGME). Page number 890 (Calasparra)
  • Geological map of Spain. E: 1/200.000 (IGME). Page number 72 (Elche)
  • Geomorphology of Spain. Different authors. Editorial Rueda, 1994.

There are no specific geological or geotechnical studies of the reservoir available, although information from different projects carried out for the dam has been collected.

The Alfonso XIII reservoir is located in the northernmost part of the Baetic System, which makes up the northwestern segment of the Alpine Peri-Mediterranean Orogen (alignment of mountain chains with asymmetric topologies created during the Cretaceous and Tertiary periods, centrifugally arranged relative to the sea; Martín Algarra, 1987).

In the Baetic Mountain System, the area under consideration is framed within the External Areas or the South Iberian Domain. The materials of such a domain cover an extensive area in the mountain system and represent a time period going from the Triassic to the Miocene. Its structure is characterized by a general detachment between the bedrock (Hercynian Paleozoic) and the deformed cover (Mesozoic and Cenozoic folds, faults and buckled strata), where the clayish-evaporitic Triassic layer acts as detachment material, and the buckled strata generally lean towards the W and NW. The Paleozoic layer does not surface, remaining at a depth of 5-8 km, and it is made up of the same materials as the Macizo Ibérico.

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

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



General geological map of the Baetic System PDF Document (4 MB)

Furthermore, it is possible to distinguish the autochthonous materials in our area of study, the relative pre-layer formations (belonging to the Miocenic period), as well as the post-orogenic formations which were deposited after the allochthonous units were placed, representing the Tertiary and Quaternary layers.

The basin rests, almost completely, on materials belonging to the External Sub-Baetic, mostly on Albian marls, marlaceous limestone and sandstone.

Furthermore, the mid basin area is transversely crossed by a strip of limestone, marl and marlaceous limestone of the Turoniensis and Senoniensis, both within the External Sub-Baetic. Due to the nature of such materials, water tightness is practically guaranteed.

The only area of the basin on the Internal Front Sub-Baetic is that nearest to the dam, where it is possible to observe gypsum marls and Keuper gypsum. This terrain is characterized by the presence of rich gypsum pits which, together with the clay it is made of, make the Triassic ground waterproof.

The Alfonso XIII reservoir has been built in an enclosure belonging to the Cretaceous Cenomatensis, practically in contact with the Triassic Keuper, as it starts some meters upstream from the reservoir.

Because of its closeness to the over-thrusting front, the geological structure is particularly complicated. Therefore, although the reservoir is set on the massive Cenomanian dolomites, it is possible to see stratified dolomites from the Turonian (Cretaceous of the Internal Pre-Baetic) and sandy limestone from the Lower Miocene (Authochtonous Tertiary); in addition to the aforementioned Keuper gypsum marl.



Downstream view of the riverbed

Seismology

Seismic hazard is different from one place to another, and it has been common practice to classify areas according to it. 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.)

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

According to the the Dam Safety Technical Guidelines. Geological and Material Prospecting Studies and taking into account the land factor (applying Seismic Resistance Regulation NCSE-2002 and by analogy with the previous instruction), the Project's calculated earthquake acceleration is 0.073•g, and it is 0.116•g for extreme earthquake.

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