Doña Ana Reservoir
Background
The Segura River Basin is, amongst all those in Spain and throughout history, the one that has suffered the greatest number of catastrophes as a result of the floods produced by rivers overflowing their banks.
There are historical references dating back almost five hundred years that speak of the disasters suffered in the area due to these meteorological phenomena, including the loss of human lives.
During the 18th and 19th centuries some works were carried out in the Segura River Basin in order to guarantee its maximum exploitation: this is the case of Puentes Reservoir, on the River Guadalentín, and Valdeinfierno Reservoir, on its tributary, the River Luchena.
At the beginning of the 20th century work started on the systematized construction of reservoirs at river headwaters, in accordance with a preliminary plan drawn up in 1887 by Ramón García and Luis Gaztelu to mitigate the devastating consequences of the Santa Teresa flood of 1875. Fuensanta and Cenajo reservoirs on the Segura river are from this period, as are Talave and Camarillas reservoirs on the Mundo river; Alfonso XIII Reservoir on the River Quípar, Santomera Reservoir on Rambla Salada, La Cierva Reservoir on the River Mula and Argos Reservoir on the River Argos.
The extension of the irrigation areas, especially in the Vega Baja and Vega Media of the Segura river caused the narrowing of the Segura river, reducing the capacity of the bed in some stretches to just 100 m³/s.
The construction of a flood abatement reservoir on the River Pliego had been studied in 1937 by the civil engineer Juan Alcaraz Pavia: the project was called Pablo Iglesias Reservoir. The construction of Doña Ana Reservoir was not envisaged in this study.
In May 1977 the “Flood Control Plan of the Segura river Basin” was drawn up. Amongst the most important works included in this Flood Control Plan was Pliego Reservoir though the Doña Ana reservoir was not included.
The impossibility of finding a suitable natural downstream boundary for the storage area on the River Pliego downriver from the confluence with the Rambla de Doña Ana, called for the building of two dams -one on the River Pliego and the other on the Rambla de Doña Ana - to achieve the best possible abatement for the River Pliego floods.
The Project for “Pliego Reservoir” was drawn up in June 1987, including the construction of a dam on the Rambla de Doña Ana wadi, as an additional closure point to Pliego Reservoir. The Reservoir is named after the wadi, Doña Ana Reservoir.
Initially two sites were identified for the possible closure point of the dam.
Site 1 was about 1,500 m from site 2, which was eventually chosen, and it was located at the start of a stretch of enclosed valley, between a hill stretched out in the direction of the riverbed on the right bank and a large alluvial terrace with considerable thickness of detritic material on the left bank.
The substrate was made up of a formation of greenish loams on both banks.
The left bank was characterized by the presence of a great deal of alluvial deposits and colluvial soils of a thick detritic and permeable nature. In the deposits of fine materials there was intense gully erosion, as well as a system of open joints parallel to the riverbed which provoked slab collapse.
The proposed downstream boundary offered a useful height limited to 6 or 8 m and a length at the crest of 150 to 200 m. The left bank rested on highly permeable alluvial deposits.
Site 2, was located about 1,500 m upriver from site 1, in an enclosed stretch of valley between two elongated hills in the direction of the riverbed and formed from an alternation of micritic limestone, clayey limestone and calcareous shale, with a course transversal to the riverbed and a dip of 15º to 20º downriver.
At this downstream boundary mechanical 15 and 18 m test drillings were performed in order to get continuous samples and Lugeon type permeability tests.
From the preliminary studies it was concluded that rock behaviour of the support formation guaranteed its carrying capacity, and that there would be no settling with the load necessary for a 20 or 30 m dam. Thus Site 2 was considered to be suitable for the downstream boundary of the reservoir.
The contract for Pliego Reservoir works project, including Doña Ana Dam, was awarded by public tendering and by Council of Ministers agreement on 14th October 1988, with a completion deadline of 36 months.
The Variation Order was signed on the 21st November 1988.
While the works were being carried out, the decision was taken to perform a series of changes with regard to what had been established in the project, amongst which was a new design of Doña Ana Dam with the following modifications:
- New design for the two height overfall spillway (Rambla del Moro type), increasing drainage capacity.
- Use of SR type sulphate resistant cement given the chemical characteristics of the water in the Rambla de Doña Ana.
- Withdrawal of the scour outlet sluice gates, converting the dam into a “hole dam”.
- Elimination of the planned right of way across the dam’s crest.
- Deeper foundations for the dam abutments.
In February 1993 the Project for Additional Works I for the Pliego Dam was drawn up which included an electrical connection for Doña Ana Dam.
Access
Doña Ana Reservoir installations are best accessed from Murcia using the N-340 main road, which joins this town to Lorca. In Alcantarilla one turns right onto the C-415 regional main road which leads to Mula, and there one takes the old C-415 road to El Niño. Here one takes the C-6 road, towards Zarzadilla de Totana, and after about 9 kilometres an access track branches off to the left to the reservoir’s left bank. This access route is the most direct and in better condition as on the right bank the track which leads to the track to El Carreño can only be used by specialized vehicles.
To get to the dam’s crest, on the left bank, one takes a short dirt track which branches off the C-6 between the villages of El Niño and Zarzadilla de Totana, both in the province of Murcia.
The left bank can be accessed using a 4X4 using country tracks.
The nearest towns to the reservoir are El Niño de Mula and Mula.
The location of the reservoir can be seen in the following map:
Characteristics
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LOCATION OF THE RESERVOIR
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Province
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Murcia |
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Municipality
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Mula |
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River
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Rambla de Doña Ana María Stream |
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Hydrographic basin
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Segura |
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DETAILS OF THE BASIN
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Surface area of the reservoir basin
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19,41 km² |
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Maximum altitude of the reservoir basin
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690 m |
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DETAILS OF DOÑA ANA RESERVOIR
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Reservoir surface area
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39,50 ha |
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Reservoir volume
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2,54 hm³ |
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BODY OF THE DAM
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Type
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Gravity |
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Materials
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Mass concrete |
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Upriver slope
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0,05/1 (h/v) |
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Downriver slope
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0,75/1 (h/v) |
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Height above course of river
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29,00 m |
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Level of crest (axis of road)
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379,16 m |
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Crest length
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180,00 m |
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Crest width
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2,40 m |
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Total volume of concrete
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40.000 m³ |
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SPILLWAY
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Number of Spillways
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1 |
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Type of spillway
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Fixed lip |
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Location
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Centre of the dam |
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Position relevant to flow direction
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Frontal |
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Situation
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On dam |
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Number of openings
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2 |
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Free length of each opening
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76,50 y 45,00 m |
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Total free length
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121,50 m |
Imágenes
Purpose
The function of Doña Ana Reservoir is that of flood control and it lacks control valves on the scour outlets (“hole dam”), its usual level being that of the same height as or below that of the scour outlets, and so the reservoir is functionally empty outside flood events.
The Rambla de Doña Ana is a tributary on the left bank of the River Pliego, in turn, a tributary on the right bank of the River Mula, which in turn is a tributary on the right bank of the Segura river.
The plan below outlines the dams existing in the Mula river basin, where it can be seen that there are none upstream from Doña Ana Reservoir.
Los Rodeos Dam is located downstream on the River Mula, following its confluence with the River Pliego, which also is used for flood control purposes.
Territorial and Administrative Context
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.
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).
Geology.
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:
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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.
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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.
Seismology.
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.
(14,3 MB)Situation
The dam and the reservoir can be found in the municipality of Mula.
The coordinates of the point where the Rambla de Doña Ana meets the reservoir comes as follows:
X 38º 01' 24" West
Y 1º 33' 10" North
The meeting point mention before has the next U.T.M. coordinates :
Reference system ETRS89. Time zone= 30
X=627.039
Y=4.209.358
