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Santomera reservoir

Territorial Framework and Management.

Physical Characteristics of the Basin.

The fundamental characteristics of the dam and reservoir of Santomera are:

Fundamental characteristics
Crest level
Reservoir capacity
26,29 hm³
Reservoir surface area
263,4 ha
Section of river regulated
5,08 km
Length of shore
28,6 km
Surface area of own basin
152,78 km²
Surface area of whole basin
500,43 km²
Maximum height of basin
1 372 m

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Geology and Seismology.

Regional Geology.

The town of Santomera lies on the northern edge of the Vega Baja del Segura, about 4 km from the river. Behind the town there is a relatively flat area of an approximate surface area of 6-7 km², which is bordered by contour limit 50, a small alluvial valley in the final stretch of the course of the Rambla Salada or Santomera which is bordered on both banks by sharp topographical reliefs. On the left, the western prolongation of Sierra de Orihuela, with heights of up to 500 m; and to the right, Sierra de Los Cantalares, not so high, and which stretches to the area around the town (Punta del Bermejo).

To the west of Sierra de Orihuela there is a series of small isolated hills or hillocks, which run as far as the natural downstream boundary of the dam.

Geology and Soils of the Storage Area.

The age of the outcropping materials in the area ranges from the Triassic, the only representative of the Secondary Age, through to the Quaternary. The lithological plan for the different formations is given below.

Triassic. The area in question forms part of the inner area of the Cordilleras Béticas, and is usually referred to as the Zona Bética. Within this, the Triassic formations represented are attributed to the Ballabona-Cucharón complex. The geological report includes in the Orihuela page three tectonic units which are designated: Túnel, Bermejo and Orihuela. In the area under study all the Triassic materials belong to the Bermejo unit, in which, in turn, the Mina formation and the Cantalares formation are distinguished.

  • The Mina formation, which is present along the main road between Campillo and Monteagudo, consists essentially of quartzites and slates with an estimated thickness of 300-400 m.
  • The Cantalares formation, which is stratigraphically above the former, is basically composed of carbonated rocks. The lithology of this formation is very variable, with 5 series being distinguished, and all of them, with the exception of the uppermost, contain limestones, dolomitic limestones or dolomites of various colours, loamy and slatey rocks. The limestones are generally very siliceous and there are quartzite banks and abundant greywacke and gypsum, the latter in banks of several metres. Where the two formations meet there appear metabasites (E1), masses of volcanic origin concordant with the carbonatic strata which locally can be dozens of metres thick.

Miocene. Only the upper part of the Miocene appears, in marine and continental facies. The reduced outcrops of grey loams and sandy limestones on the right bank of the Santomera reservoir are attributed to the Tortonian age, and these are marine sediments which run laterally to a continental conglomerate complex. The gypsiferous loams which occupy the north-western part belong to an ample outcrop, dated as Andaluciense, and which are assigned a thickness of about 400-500 m. Locally they are topped by continental horizons of little thickness, like that which can be seen at the tail-end of the reservoir.

Geology and Soils of the Natural Downstream Boundary.

The dam rests on its right abutment on the conglomerate formation, pudding stones of great thickness, composed of not very rounded stones from the Triassic age. These conglomerates, concordant to the north with the Andaluciense loams, further south form the only Miocene representation. They lie directly on the Triassic in the area between the reservoir and Los Cantalares hill.

The left abutment of the dam lies on limestone with a certain degree of fissuring, which has been the cause of important seepage on different occasions during the life of the dam.

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