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Doña Ana reservoir

Territorial framework.

Physical Characteristics of the Basin

Doña Ana Reservoir is located on the Rambla de Doña Ana María, a tributary of the River Pliego, which in turn is a tributary of the River Mula.

From its source at El Carretero until Doña Ana Reservoir it runs 9.3 km. The average gradient over its course is of 2.41% and the surface area of the basin is 19.41 km².

With regards to Doña Ana Reservoir’s specific catchment basin we can point out that:

  • The highest areas of the basin are situated to the North, such as La Canticharria (509 m), El Arrebolao (557 m), the Cerro Rodero (the highest point of the catchment basin at 690 m).
  • To the East, South and West the mountainous areas are lower than to the North, such as El Carretero and La Zapatilla.
  • Near the course of the river the landscape is of plains spotted with hills

The catchment basin for Doña Ana Reservoir is all located within the province of Murcia and in the Municipality of Mula. Within this area there are no towns or villages.

The only road which crosses the basin is the C-6, which joins the village of El Niño with the MU-503 road.

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Environmental information.

The area is covered by large expanses of woodland where vegetation typical of the Mediterranean forests can be found, dominated by the Aleppo pine (Pinus halepensis), xerophilous bushes (esparto grass, wild asparagus, buckthorn) and herbs (rosemary, thyme, lavender), etc. On the planes, close to the stream there is farmland which mainly grows almonds, apricots, vines and olives.

The peaks of Sierra Espuña, close to the basin are dominated by the golden eagle (Aquila chrysaetos) and the chough (Pyrrhocorax pyrrhocorax). In these high areas it is easy to spot the Barbary sheep (Ammotragus lervia), a hunting species introduced in the Parque Natural de Sierra Espuña from Morocco.

Farmlands are inhabited by the swallow (Hirundo rustica), the white wagtail (Motacilla alba), the kestrel (Falco tinnunculus), besides mammals such as the field mouse (Apodemus sylvaticus) and amphibians such as the common salamander (Salamander salamander), the common toad (Bufo bufo), the Iberian water frog (Rana perezi) and the European tree frog (Hyla arborea).

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Regional geology.

The river basin where the Doña Ana dam is situated is formed by the Pre-Baetic materials of the Mula unit. It is located between formations from the Malaguide Baetic Complex of the Sierra de Espuña to the Southeast and Sub-Baetic materials from the Sierra de Ponce to the West. The Malaguide materials range from the Paleozoic era until the Eocene and are hardly affected by Alpidic Metamorphism. The Sub-Baetic materials go from the Triassic period to the Oligocene and do not present metamorphic features. The Neogene and Quaternary materials occupy a series of corridors that separate the various mountain ridges made up of Baetic materials.

The Mula unit belongs to Sub-Baetic - Pre-Baetic geotectonical area which is characterized by tectonics with surface principal structures and numerous low-angle thrust faults, this area having an important seismic activity.

The Mula unit is mainly composed of a succession of materials ranging from the Oligocene period to the Upper Miocene and Quaternary.

To the east of Sierra de Ponce there are Oligocene formations consisting of a thick series of loamy limestones characteristic of a lacustrine sedimentation, followed by compact limestones with Lepidocyclina, which are followed, discordant, by some molassic limestones, possibly from the Aquitanian period.

To the north of the Sierra de Espuña or south-southeast of the Mula unit, the formations of the Pliego river basin appear. On the Oligocene base these feature some reef limestone and conglomerates, followed by the Lower Oligocene formed by ochre loams with alternating detritic levels. This is followed by the Upper Oligocene which is basically coastal with strong continental influence, composed of shales, limonites and sandstones, with the appearance also, though clearly discordant, of some molassic limestones from the Aquitanian period.

Above these materials, to the west, there are deposits from the Middle Miocene, formed by greenish-grey loams and conglomerate sandstones of calcareous cement; to the east and in the vicinity of the town of Pliego, there are elements from the Upper Miocene, being discordant on the Lower Miocene; in this case, they are formed by loose clays, conglomerate sands and some levels of molasses.

The existing terrace deposits, fluvial alluvium and loose hillside soils are from the Quaternary, Holocene, period.

Doña Ana Reservoir is located on Map 72, of the geological map of Spain, of the Spanish National Geographical Institute at a scale of 1:200,000. Plan 1.5 shows the regional geography of the River Mula Basin through Maps 72 and 79 of the geological map of Spain at a scale of 1:200,000.

Geology and Geotechniques of the natural downstream boundary

a) Stratigraphy.

This area is made up of a monoclinal carbonated type series, covered in the flat areas by recent alluvial deposits, and on the hillsides by colluvial type deposits.

The lithological units that form the downstream boundary are the following:

  • Cretaceous. Loamy limestones

    This consists of a series of dark grey loamy limestones, stratified in packs, not more than 1 m thick, and levels of 30 to 40 cm thick light grey loamy limestones which were much more cemented and more resistant to excavation.

    The degree of hardness depends on the carbonated cement content as well as the degree of alteration, which is higher in the lower levels, closer to the riverbed.

    The samples were defined as fine grain fossiliferous loamy limestones, slightly sandy, with quartz grains whose proportion was between 3 and 5 %, with the degree of hardness depending solely on the carbonated cement content.

    The hard loamy limestone strata are not more than 40 cm thick, and are affected by numerous joints and faults which produced small movements relative to the blocks.

  • Quaternary.

    They consist of alluvial deposits which cover the valley floor and which are due to the fluvial dynamic of the wadi and the colluvial deposits due to the gravitational dynamic of the hillsides.

    There are three units situated within the quaternary:

    In the first unit, and the most modern of them, we can find light brown silty sands, which are between 3.5 and 4.0 m thick. This deposit lies, discordantly, on a level of gravel and is mixed with hillside deposits.

    The second unit is made up of sand and rounded limestone gravel. The thickness of this level varies, being less than a metre thick except for on the right bank where it reaches 3 m as this is an old paleobasin area. The base of this level is the cretaceous loamy limestone formation.

    And finally there are hillside or colluvial deposits, covering and hiding the cretaceous formations around the downstream boundary. These are less than 1 m thick and are made up of loamy clays with numerous fragments of heterometric rocks.

b) Structure

The rocky wall is characterized by a monoclinal structure with an approximately N-S orientation in the stratification with a dip that varies between 10º and 20º towards the NE.

The foundations are affected by four different families of joints, mainly smooth, undulating, of variable spacing, closed or grouted with yellowish crystalline calcite except for the most superficial ones which are open because of the effects of decompression and the effects of water or damp where they are nearby. The characteristics of these families are

  • The first family varies in direction by about 15º, being situated between 30º and 45º E, with the dip varying between 80º and 90º SE.
  • The second family has a directional dispersion of 5º, being situated between 55º and 60º E and a dip which varies between 80º and 90º NW.
  • The third family varies about 20º in direction, being located between 110º and 130º E, with a dip which varies from 70º to 90º NE.
  • The fourth and last family, is located between 165º and 180º E, with a dip of between 65º and 90º NE.

During excavation other joints were found, but as they did not appear systematically were not classified in any of these families.

The rocky wall is also affected by a system of faults, both vertical and normal which have provoked small relative movements in the blocks, without any one jump being greater than one metre. Similarly, in some cases, mylonitized clayey material has been observed in the fault planes.

c) Permeability

The in situ permeability tests performed by the Geological Service show that, disregarding recent deposits, the foundation land can be considered impermeable for the purposes of a reservoir; however, due to the alteration and decompression phenomena, there may be areas on both hillsides which could favour the focussing of moderate water losses.


Doña Ana Reservoir is located between the municipal district of Mula, for which Annex 1 of Seismoresistant Construction Regulations NCSR-02 establishes a basic seismic acceleration of 0.09 g, the aforementioned Regulation therefore being applicable.

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