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Reservoirs

Cenajo reservoir

Territorial and administrative background.


Physical Characteristics of the River Basin

The total catchment area of the Cenajo dam occupies an area of 2,602.4 square kilometres, of which 1220.6 km² correspond to the basin of the La Fuensanta dam, located upstream. The basin of the Cenajo dam itself, therefore, has an area of 1,381.8 km².

The whole basin lies at an average altitude of 1107m and is spread over the provinces of Albacete, Murcia, Jaén and Granada. The main tributaries of the Segura river in the basin are the river Zumeta,river Tus( which flows into the Segura in the Fuensanta reservoir) and river Taibilla.

The Camarillas reservoir has a surface area of 1732 ha at its usual maximum contour height, and all of the area lies within the municipal districts of Hellín,Socovos and Férez, in the province of Albacete, and Moratalla in Murcia province. The capacity of the reservoir at the given contour is 437 million cubic metres. The perimeter of the reservoir measures 72 km, while the length of the bed inundated by the reservoir is 31 km.

Vista general de la presa y embalse del Cenajo

Vista general de la presa y embalse del Cenajo

The main characteristics of the Cenajo reservoir and its catchment area are detailed below.

Catchment basin
Surface area of own basin: 1.381,8 km²
Surface area of whole basin: 2.602,4 km²
Average altitude of whole basin: 1.107 m
Average altitude of own basin: 969 m
Maximum altitude of basin: 1.860 m
Average annual rainfall: 325 mm
Runoff: 0,24
Average water collected annually in the basin: 298 hm³
Maximum recorded flood: 160 m³/s
Reservoir
Maximum normal level altitude (NMN): 433,40
Projected flood level (NAP): 435,00
Minimum level of Exploitation : 355,78
Total capacity (at NMN): 437,35 hm³
Total capacity (at NAP): 465,59 hm³
Reservoir surface area (at NMN): 1.732 ha
Section of river regulated: 31,00 Km
Length of shore: 72,13 km
 

The basin catchment area has been marked and measured in accordance with the 1:50,000 scale map published by the Servicio Geográfico del Ejército. The surface area of the reservoir and the stretches of river dammed and shore have been obtained through direct measurement on a 1:2,000 scale map developed from a photogrammetric flight over the reservoir in April 2003.

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Environmental information

El Cenajo reservoir is located between the provinces of Albacete and Murcia, and therefore it is geographically divided between the autonomous communities of Castilla-La Mancha and the Region of Murcia.

Vista parcial del cuenco de amortiguación en la que se incluye el azud de aguas abajo y la caseta de válvulas de regulación de la toma

Vista parcial del cuenco de amortiguación en la que se incluye el azud de aguas abajo y la caseta de válvulas de regulación de la toma

El Cenajo dam and reservoir do not form part of the networks of protected areas of either of the two autonomous communities. However, we should point out that downstream from the reservoir, following the course of the river, we have the Site of Community Importance (SCI) known as LIC de las Sierras y Vega Alta del Segura y Río Benamor, declared as such by agreement of the Governing Body of the Region of Murcia on 28th July 2000. SCIs are areas of unspoiled nature resulting from the application of the European Birds and Habitat Directives (79/409/EEC and 92/43/EEC), which are characterized by contributing significantly to preserving or restoring a type of natural habitat or a species in a favourable state of conservation within the biogeographical region to which it belongs.

Due to the dates on which the dam projects were drawn up and its construction was carried out, the dam was not submitted to any type of environmental impact study. However, we must highlight that there have been numerous actions carried out for the reforestation of the reservoir banks promoted by the Confederación Hidrográfica del Segura over a period of many years. These were done in areas such as Alcantarilla de Jover, Casa Requena, Rambla de los Cuartos, etc., all directed by the engineer of the Confederación Hidrográfica del Segura Mr. Luis Aycart Benzo.

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Geology and seismology

Regional geology

The oldest formations that we find in the region date from the Triassic period, whose “Keuper” facies form a unit lithologically consisting of clays, siltstones and gypsiferous loams, in which the thick layers of gypsum that have favoured the diapiric processes may vary. This formation appears dispersed in small outcrops in the surroundings of the Reservoir, their thickness being difficult to specify.

The Jurassic period is well represented in the area in question due to a monotonous series of dolomites of a massive, granular, aspect, with medium to thick grain, which usually present a brecciated appearance due to the secondary processes of dolomitization and which, in the area of the natural downstream boundary, and on the right riverbank of the Reservoir, appears loaded with terrigenous sediments (quartz gravel and sand) with irregular distribution in the vertical area.

This stretch presents abundant current structures partially eroded by diagenesis, although channels can be seen with stratified filled grooves and lags with quartzite stones, and therefore the sedimentary environment could be of a sub-tidal nature. It is estimated as being about 50 metres thick.

Another level well represented in the region, mainly to the north of the Segura river, and covering the whole left riverbank of the Reservoir in question, is the Upper Miocene-Pliocene, formed by sedimentary deposits in the Segura River Basin, with total thicknesses of about 500 metres.

Paramento de aguas arriba de la presa desde la margen derecha en la que se aprecia el conducto del limnímetro

Paramento de aguas arriba de la presa desde la margen derecha en la que se aprecia el conducto del limnímetro

A first stretch is lithologically formed by conglomerates and sandstones from the Jurassic period, from the detritic deposits of the Lower Cretaceous period and the Marine Miocene, with some carbonatic layers. Next to the natural downstream boundary, they are about 90 metres thick. They probably correspond to the Middle Tortonian age (Upper Vallesian), since only remains of spicules and algae without any cronostratigraphic value have been observed.

A second stretch, well developed in the region, is formed by white clayey loams with evaporites, in which small levels of lignite and sulphur can be found locally, which were intensely exploited in the past, currently having been abandoned.

This stretch, with thicknesses of between the 150 and 200 metres, may contain levels of Globigerins that show a connection of this area with other marine ones or with a resedimentation of the Marine Miocene period, being deposited as fragments of calcareous rocks.

Lastly, we can find another stretch lithologically formed by white folded limestones and loams that, occasionally, include some sandy levels. On the roof of this stretch, there are abundant levels of diatomites that are intensely exploited in the vicinity of the reservoir.

Their thickness is about 250 metres. Their age has been determined thanks to the abundance of fossil remains (micromammals, fish, gastropoda), very well conserved in the core of the diatomites and the associated loamy levels, which allow us to identify this stretch as belonging to the Upper Turolian (Messinian) stage.

Seismology

The Seismoresistant Construction Regulations NCSR-02, approved by means of Royal Decree 997/2002, in Section 2.1 include a seismic hazard map. This hazard is expressed in accordance with the basic seismic acceleration “ba” – a characteristic value of the horizontal acceleration of the land surface in accordance with the gravity acceleration “g”- and the “K” contribution coefficient, which takes into account the influence of the different types of earthquakes expected regarding the seismic hazard of each area.

The range of “ba” values in the areas of our country with seismic hazard is between 0.04 g and 0.24 g, and the “K” value is between 1.0 and 1.3.

In accordance with the aforementioned map and Annex 1 of the Regulations, which includes a list of “ba” and “K” values in different municipal districts of Spain, the characteristic parameters of the seismic hazard in the area of the Cenajo reservoir are the following: ba=0.07 g; K=1.0.

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