Access

The access to the dam and reservoir area is along the MU-531 local road joining the towns of Alguazas and Campos del Río. From this local road, in the direction of Alguazas-Campos del Río, km 6.400, take the diversion, going south-west, to Los Rodeos reservoir, the access road being on the left bank of the reservoir. This access road is approximately 1,320 m long as far as the left abutment of the dam and is 6 m wide with two-way traffic, a transversal gradient of 2% toward the verge and 4% from the latter to the ditch. The road has 1 m verges, with ditches dug in the stretches where they are necessary

The access on the right embankment of the dam is along the N-344 main road until reaching the town of Las Torres de Cotillas. Once here, take the road west in the direction of Campos de Arriba as far as km 3 + 100 to Campos de Abajo. From here, take the road going north-west and about 4,000 m later you will find the right embankment of the reservoir.

Therefore, the dam has two accesses, one, on the left embankment, along the Alguazas road, and the other one on the right embankment, taking the turn-off from the road leaving the town of Las Torres Cotillas.

The location of the reservoir can be seen in the following map:

Characteristics

Imágenes

Purpose

The function of Los Rodeos Reservoir is that of flood abatement, its usual level being the same as or lower than the level of the scour outlets, and so the reservoir is functionally empty outside flood events.

Enlarge image

The River Mula is a tributary on the right of the Segura river.

The graph enclosed shows an outline of the dams existing in the Mula river basin, where it can be seen that upstream from Los Rodeos Reservoir we have Pliego Reservoir and Doña Ana Reservoir – also as a retarding basin – and La Cierva Reservoir, and that there are no dams downstream.

Territorial and Administrative Context

Physical Characteristics of the Basin.

The River Mula is a result of the confluence of various wadis and streams coming down from the mountain ranges of Burete, Lavia, Ceperos, Plaza de los Pastores and El Charco, in the municipal districts of Bullas and Cehegín. It flows to the north of the city of Mula and, shortly before reaching La Puebla, is joined by the River Pliego, which drain the northern slope of Sierra Espuña and the eastern one of Sierra del Cambrón. It flows through Albudeite and Campos del Río, is the boundary between the municipal districts of Alguazas and Las Torres de Cotillas, and flows into the Segura alter having flowed 64 km at a height of 62, 253.30 km from the source of the Segura river. The average gradient is 12.90 per thousand and its total basin area is 661 km².

The geographical structure of the basin is formed by plains and undulating reliefs, with scattered small hills and drainage through wadis and ravines that converge in two watercourses, the River Mula and the River Pliego. To the north, the territory is bordered by the Sierra de Ricote, and from the South-west to the South-east, by the Sierras del Cambrón, Espuña, La Muela and El Cura, the last two outside the district.

The centre or interior of the Basin shares a series of common characteristics. For example in Campos del Río, except in its northern area, Miocene deposits abound, mostly loamy ones, which have been highly eroded, thus resulting in the typical landscape of arid regions and, in short, of this basin, such as the landscape of badlands or ravines. The same occurs in Albudeite, where the highly uneven topography with numerous ravines, wadis, and gullies carved in those semi-impervious Miocene materials leads to a landscape of badlands. The loamy and clayey materials of Mula have also suffered that process. The fields of Pliego, located in the southern centre of the Mula Basin, next to the northern slope of Sierra Espuña, do not present this badland modelling. These lands have a similarly uneven topography, but are conditioned by their location on the southern slope of the Basin.

The River Mula is of a torrential nature, this feature being even more emphasised by the lack of vegetation and the loamy nature of its basin. Because of the steep gradient of the course, its floods are huge avalanches of water transporting a solid sediment load.

The catchment basin is located entirely within the province of Murcia, and the towns of Pliego, El Niño, Baños de Mula, Campos del Río, Yechar, Albudeite, Mula, and part of the built-up area of Bullas form part of its area.

Pliego, Doña Ana and La Cierva reservoirs are also situated within the basin.

As for Los Rodeos reservoir, the surface area of the catchment basin as far as its intersection with the dam, is 647.29 km² and the surface area of the storage area upstream the dam to the overfall spillway is 158.08 ha, with a corresponding volume of 15.01 million cubic metres.
 

Environmental Information.

The extreme aridity of the area means that the natural topsoil is scarce, xerophite and thermophile; it has been even more affected by human activity. Only stunted thickets of albardine, thyme and esparto grass are found in the eastern sector. Toward the west, thickets of rosemary and some patches of pines appear. Only in the mountainous areas that surround the District can we find pine groves. We must highlight the northern hillside of Sierra Espuña covered in gall-oaks, as well as Corsican pines, and also some holm-oak groves in the same area.

The main characteristic of the Mula river basin lands, being as it is an arid Mediterranean landscape, is the increasing use, in accordance with its topographical characteristics, of more lands for crop growing.

If the Mediterranean ecosystem is characterized by some not-so favourable factors for the development and maintenance of wooded masses in this district, due to the special characteristics of its climatology, a more unstable and vulnerable situation is reached due to the addition of the geomorphological, edaphic, ecological and negative anthropic factors. The latter contribute exceedingly to the disappearance of wooded areas.

Its fauna appears related to the plant formations that make up their natural habitat, being strongly interrelated. Among the species that inhabit the area in question, we can mention the following:

• Mammals: the Granada hare (Lepus granatensis); the European rabbit (Oryctolagus cuniculus); the wood mouse (Apodemus sylvaticus); the house mouse (Mus musculus); the water vole (Arvicola amphibius); the weasel (Mustela nivalis).
• Birds: the kestrel (Falco tinnunculus); the red-legged partridge (Alectoris rufa); the quail (Coturnix coturnix); the woodpigeon (Columba palumbus); the turtledove (Stretopelia turtur); the swift (Apus apus); the raven (Corvus corax); the magpie (Pica pica); the skylark (Alauda arvensis).
• Amphibians: the common salamander (Salamander salamander); the common toad (Bufo bufo); the Iberian water frog (Rana perezi); the European tree frog (Hyla arborea).
• Reptiles: the Iberian wall lizard (Pordacis hispanica); the common lizard (Lacerta lacerta); the eyed-lizard (Lacerta lepida); the green lizard (Lacerta viridis), Latastes viper (Vipera latasti).
• Macro invertebrates: (Tubelaria; Decapoda; Amphipoda), insects such as Belostoma elongatum (Ephemeroptesa, Trichoptera, Heteroptera), the great diving beetle (Coloptera), flies and mosquitoes (Diptera).

Geology and Seismology.

Regional Geology.

The Mula river basin is part of the Cordillera Bética-Rifeña mountain chain, a great geotectonical unit in the form of a wedge with its vertex orientated westwards, which closes in the so-called denominated Arco de Gibraltar and whose roots are hidden beneath the waters of the Mar de Alborán.

The mountain chain has its origin during the Lower and Middle Miocene, caused by the collision of the African and Iberian plates due to continental drift, the Alborán microplate playing an important role.

The area in question belongs to the Post-mantle Miocene of the unit known as Prebético Interno de la Cordillera Bética.

Lithostratigraphy: Lithologically-speaking, the materials appearing in the area in question, beginning with the oldest, are:

• Upper Miocene
  
  They are a group of loamy materials, with few calcarenitic intercalations, of a marine nature, and which are attributed to the Tortonian and the Andaluciense ages using micropaleontological criteria.
  
  This Miocene period is represented by the following formations:
  
  - Formation of Lower Loams. (t1). These are calcareous loams of a greenish-grey colour and conchoidal fracture of very fine grain and of a massive nature, its stratification not being easily appreciated.
  
  - Formation of Upper Loams (t2). This appears on the roof with the previous formation, downstream from the boundary for the storage area, and so it is not wet by the reservoir, or if it is, not very much, but part of the dam has its foundations on it.
  
  They are loams somewhat more clayey than the lower ones, of a similar colour and have alternating centimetric levels of calcareous loams, which means that is easy to distinguish the stratification. They are less massive than the previous, and in some places layers of white fibrous gypsum appear, not very thick, of only a few millimetres in the natural downstream boundary, although about 2 km to the NE (Loma de las Yeseras) there are layers of gypsum of between 0.5 to 1.5 m thick, layers that have to wedge themselves or become narrower toward the area of the reservoir.
  
  The base or wall of this formation (in contact with the underlying Lower Loams) has been located in the calcarenite layer that appears in the ravine, although the transit between them is gradual, there being a stretch of slightly clayey loams, with intermediate characteristics. The roof of the formation does not appear in the area, but it can be affirmed that it is several hundreds of metres thick.
  
  - Calcarenite layers (ta). Inserted in the loams of the two previous formations we find hard strata more resistant to erosion, formed by decimetric to metric layers of calcarenites and calcareous microconglomerates, bioclastic limestones with gastropod shells and oyster lumachelles that alternate with calcareous loams in metric layers.
  
  These harder layers can reach a thickness of 6-8 m and are what make up the Mula valley ravine and the summits of the small surrounding mountain ridges.
  
   
• Pliocene-Quaternary
  
  - Formation of rosy-coloured silts. This formation lies subhorizontal on the Miocene loams, the contact between both being an old eroded surface with strong relief, which means that contact varies between 0 to 50 m over the level of the River Mula.
  
  It is a heterogeneous formation, not consolidated, of gravels, conglomerates, fine silty sands, loamy silts and clayey loams.
  
  The gravels and conglomerates appear mainly in the lower part of the formation, resting on the Miocene loams, although there are also discontinuous levels in the upper part, corresponding to elongated bodies of fluvial paleochannel beds.
  
  The silty sands are of very fine grain, and have a characteristic rosy tone, being distinguished very well from a distance. (They are locally called arena bruja). Lastly, the clayey loams are yellowish and white in colour, not much consolidated and can at first sight be confused with the alteration loams of the loamy formations described. They are on the upper part of the formation.
  
  The thickness of the formation and its different lithologies is very variable, since its roof has been eroded. The maximum thickness observed was about 25 m, and that of its basal conglomerate part, about 15 m.
  
   
• Quaternary.
  
  - Terraces. (q1, q2, q3). Three levels of terraces were observed in the Mula valley, located 3, 6 and 10 m approximately over the current level of the bed.
  
  Their main lithology is clayey loams, including pebbles that are not very abundant except on the base, where a thin discontinuous level of gravels can be found. The maximum thickness observed was about 4 m.
  
  - Alluvial. (qa). The current gravel deposits of the River Mula are mainly heterometrical ones with limestone pebbles, and to a lesser extent, silty sands, deposited in the convex part of the meanders. Their thickness, deduced from the probing data, did not exceed 2 m.
  
  - Wadi bed deposits. (qr). These are whitish loamy clays, coming from the alteration of the Miocene loams and deposited by the streams at the bottom of the wadis that end in the River Mula, which means these small valleys have a flat floor.
  
  - Alluvial fans. (qc). They are formed in the mouth of the wadis on a surface of terraces on the left riverbank of the Mula upstream from the ravine. They are less than 1 m thick.
   
• Structure and Fracturation
  
  The formations of the Upper Miocene or “Post-mantle Miocene” which, in the area, are more than 1,000 m thick, are laid out forming a monocline series dipping uniformly between 15º and 25 º to the SE or SSE. The direction of the dip varies between 140º and 170º, that is, downstream of the River Mula, so that the oldest materials (t1 formation) appear toward the tail end of the reservoir, and the most recent (t2 formation) toward the downstream boundary for the storage area.
  
  Over the previous ones lies, subhorizontal, the formation of rosy-coloured Plio-Quaternary sands (pq formation) whose lower limit is an old eroded surface, with strong paleo-relief, which means that its base is at a different level according to the place. The formation fills and makes the paleo-relief and its upper part uniform, frequently cemented and resistant to erosion, of current morphologies of hills with a flat summit.
  
  The previous materials lie, also discordant, on Miocene loams and in some cases, on the rosy-coloured silts of the pq formation.
  
  Fracturation is very not very significant. The loamy formations behave plastically to the tectonic activity, there not being hardly any fractures in them. In the calcarenite layers (ta), fractures are more frequent, with a maximum vertical fault of 2.2 m, NE-SO and subvertical dips of about 30º to the NO.
  
  Landslides are not very frequent and they involve small volumes of material.

   

  
   

Geology and Geotechniques of the Storage Area Upstream of the dam.

The geology of the storage area upstream of the dam coincides with that indicated in the section on regional geology.

Summarizing what has been said in the previous section, this area is made up of massive calcareous loams from the Upper Miocene with scarce, thin intercalations of sandy limestones, fossiliferous and calcarenite limestones, which produce the slight narrowings of the valley.

The layers of loams and calcarenites dip uniformly to the SE between 15º and 25º.

The upper parts of the valley hillsides are covered in a Plio-Quaternary formation of rosy-coloured silts, with clayey loams and some conglomerates, not very cemented, which lie subhorizontal and discordant on the Miocene, reaching a thickness of 25 m in some places.

Other materials present, not so thick, are three levels of clayey-loamy terraces, some gravels, alluvial deposits of sands and gravels with silty matrix and covered in clayey loams of alteration of the substratum in the form of wadi bed deposits and alluvial fans.

The materials of the storage area upstream of the dam are practically impervious.

Fracturation is not very frequent and its orientation corresponds to regional tectonic guidelines.

Landslides occurred in the area are not very relevant, in spite of the abruptness of the valley hillsides.
 

Geology and Geotechniques of the Natural Downstream Boundary for the Storage Area.

Stratigraphy.

This area is the result of the formation of Upper Loams and calcarenitic layers, although very near it, upstream, there are Lower Loams.

The valley floor is filled with terraces and recent alluvial deposits, while the hillsides are almost totally covered in Plio-Quaternary silts and loams, recent silty sediments and loams of alteration of the substratum.

The lithological units that form the downstream boundary are, from older to more recent, the following:

• Upper Miocene Loamy Formations
  
  - Lower loams. (T1). They correspond to the upper part of the t1 formation described above. Their highest part is formed by slightly sandy grey loams that behave in a compact way, no alterations being detected deep down.
  
  - Calcarenitic Layers. (Ta). Four hard layers were detected, inserted between the upper and lower loams, the thickest being 6.0 m.
  
  They are micritic limestones and fossiliferous sandy limestones, lumachellic limestones and grey calcarenites of thick grain, the latter lithology prevailing. They are quite compact, except in some thin stretch of lumachellic limestones, which are more porous and may present symptoms of incipient Karstification.
  
  - The percentage of hard layers in comparison with the total number of layers is low, approximately 30%, giving the terrain greater rigidity.
  
   
• Upper Loams. (T2).
  
  They correspond to the t2 formation described above. The content of gypsum in the downstream boundary for the storage area is somewhat higher than usual, but is insignificant regarding possible phenomena of swelling due to hydration-dehydration. These loams are slightly more changeable than the Lower ones, changing to light brown loamy clays.
• Plio-Quaternary silt formation
  
  . Gravels and conglomerates. (Pg). In the base of this formation and sometimes inserted in its lower part, there are usually discontinuous layers of gravels and conglomerates. Their thickness can vary a lot in just a few metres, existing rather abrupt lateral contacts with the rosy-coloured silts that lie above and to the side. The maximum thickness observed is 2.50 m.
  
  These materials are quite constantly present in the base of the formation, although they are not always found, and so, in these places, rosy-coloured silts lie on the Tertiary loams.
  
  They are conglomerates of heterometrical pebbles, mainly limestone, although some of them are made of quartz, pudding stone, ophite, etc., usually included in a loamy-clayey matrix very often strongly cemented by carbonates, and so being highly compact and resistant.
  
  Due to their loamy matrix, they should be considered impervious.
  - Sands and rosy-coloured loams (P1). They are fine sands, loamy-silty clays and loams that correspond to old flood plain fluvial deposits. They are not much consolidated, unless they have been cemented later.
   
• Quaternary fluvial deposits
  
  - Terraces and alluvial deposits. (Qa). They are the current alluvial deposits and terraces of the River Mula. They are loamy clays and sands that include heterometrical pebbles, very abundant, the percentage of matrix clearly prevailing.
  They can be found on the valley floor and have a maximum thickness of about 3.00 m.
  
  Recent wadi bed deposits and coverings.
  
  - Silts and loams. (Qr). This refers to the materials coming from the recent alteration of the substratum, whether transported or not. They are deposits that are not very thick (1 m maximum) of clayey loams and plastic silts, which flow easily when saturated.
  
  - Silt sediments. (Qc). They are the same materials as above, but very recently have experienced a short transport, in the form of mud outflows, in favour of the slope. They are located on the upper part of the left hillside of the valley and are not very thick.
  
  - Hillside erosion. (Q1). They are collusions and alluviums formed by loamy clays with angular calcarenite pebbles. They are not very thick, around 1 m, and are on the middle part of the right hillside.

Geological structure of the layers..

- Tertiary rocks structure.

The lower and upper loams and the calcarenitic layers form a monocline series, dipping toward the SE between 20º and 25º, with some exceptions, and so the orientation of the layers is practically perpendicular to the river bed in the area of the downstream boundary for the storage area.

- Plio-Quaternary structure.

The formation of rosy-coloured silts, in many places with their base of gravels, lies on the Tertiary loams, the contact between both being an old eroded surface, more or less curved, and in general dipping toward the valley.

The inside layers are subhorizontal, except on the edges of the paleo-channels, where they can have dips of up to 30º toward their axis. The lateral changes of facies and lithology are very abrupt, a lower part of gravels and conglomerates being observed, a middle part of silts and an upper part of silty-loamy formation.

Seismology.

Los Rodeos reservoir is located within the municipal districts of Alguazas and Las Torres de Cotillas, for which Annex 1 of Seismoresistant Construction Regulations NCSR-02 establishes a basic seismic acceleration of 0.14 g, the aforementioned Regulation therefore being applicable.

On the other hand, the National Seismic System Accelerograph Network has installed a series of accelerographs in the area near the epicentres of the Bullas series (MU), many of which are connected via telephone with the IGN data reception and processing centre (Madrid). This allows to obtain the acceleration data from those accelerographs in a relatively short time following the detection of an earthquake.

The equipment connected by telephone are 18-bit resolution GEOSIG GSR-18 accelerographs with continuous updating of their internal clock through a GPS receiver.

The table below includes earthquakes higher than 3.5 (Richter scale) in the region of Murcia.

One of the most recent occurred on 06-06-2002, registering 4.6 on the Richter scale and with an intensity V.

Planos

Plans

• Geographical (401 KB)
• Cross-section (754 KB)
• Base of the reservoir (4,4 MB)
• Base of the reservoir II (1 MB)
• Elevations (215 KB)

Ortofotos

• Presa del embalse (6,7 MB)
• Vaso del embalse (6,7 MB)

Situation

The dam and reservoir are located within the municipal districts of Alguazas and Las Torres de Cotillas.

The coordinates of the point where the river Mula meets the reservoir comes as follows:

U.T.M. coordinates :

Reference system ETRS89. Time zone= 30
X=649.662
Y=4.212.009

Geographical coordinates (based on the Greenwich meridian):

X 38º 02' 39" West
Y 1º 17' 35" North