Logo of the Confederación Hidrográfica del Segura, go to home page

 You are in :: Inicio > Information > Infrastructures > Reservoirs > Puentes

Reservoirs

Puentes Reservoir

Territorial Framework.

Physical characteristics of the basin.

The River Guadalentín catchment basin is located in the south-western area of the Region of Murcia, between the Sierras de Lavia, El Cambrón, Espuña and El Cura, to the North, and the Sierras de Las Estancias, La Carrasquilla, Almenara and Carrascoy to the South and South-east. The watershed of the Guadalentín river basin intercepted by the Puentes dam is located at La Selva bench mark, in the Sierra del Cambrón, to the North, and at Los Tonosas, to the South of Vélez Rubio, in the eastern foothills of the Sierra de Las Estancias, to the South.

The catchment basin intercepted by the dam has a surface area of 1,424.7 km² and stands between 410 metres above sea level in the ravine and the height of 2,045 metres above sea level on Cerro Poyo, in Sierra de María, at the headwaters of the River Caramel or Alcaide. The average annual rainfall in the basin is 320 mm.

The whole surface of the reservoir lies within the municipal district of Lorca. The creation of the reservoir required the construction of the main dam, on the River Guadalentín, upstream from the existing dam, and the closing, by means of a side embankment of loose materials, of the hill located to the NNW of the left abutment of the main dam, at the headwaters of the stream bed on which the area where the dam personnel live is located.


up

Geology and Seismology.

Regional Geology.

Puentes Reservoir is built on sedimentary lands deposited in the depression of Lorca, delimited by the Sierras de Las Estancias, Tercia and Espuña. These mountain ranges are completely part of the Baetic Zone, and are essentially characterized by the existence of widespread strata subsidence.

The post-mantle silts are laid discordant, in the area of the reservoir, on Baetic materials (Sierra de las Estancias), or on the Alquería Unit, belonging to the Subbético Interno. Both units are in the eastern area of the Cordilleras Béticas.

Puentes Reservoir is to the North of the eastern end of Sierra de las Estancias (“Baetic Zone”) at its boundary with the Sierra de la Alquería (“Internal Baetic Zone”).

The following geological units have been identified on its banks:

  1. Sierra de las Estancias located to the S-SW, of very complex geology formed by different sedimentary deposits (conglomerates, sandstones, limestones, dolomites….) and metamorphic materials (quartzites, slates and red argillites). The post-mantle silts (Miocene) of Puentes Reservoir lie discordant on these materials.
  2. Intermediate Area (Oligocene-Middle Miocene), located on the left and right banks of the River Corneros, to the west of the Reservoir, and mainly formed by loamy materials with intercalations of turbiditic sandstones, which are easily eroded, subject to landslide and with low permeability.
  3. Subbético Interno (Sierra de la Alquería, Lower Cretaceous-Oligocene), to the north-west and north of the Reservoir. 5 formations have been distinguished (S1-S5) of a different age and lithology, but the loamy-calcareous component prevailing in all. Of them, the S-1, made up of loams and dark, very plastic green clays, together with the S-3, of similar lithology, are the most easily eroded areas of this Subbético Interno. The S5 are potentially the most permeable (calcareous) ones, although no field or laboratory data regarding their real level of permeability and porosity are available on that area in question.
  4. Post-mantle silts that lie clearly discordant on materials of the Subbético Interno (Sierra de la Alquería) and the Baetic (eastern end of the Sierra de las Estancias), on both embankments of Puentes Reservoir. They are formed by calcareous, loamy and sandstone materials and, overlying these materials, Pliocene and Quaternary deposits that appear on the N and NE of the Reservoir, in its central part and especially on both banks of the natural downstream boundary for the storage area.
  5. Calcareous and sandstone materials corresponding to the post-mantle silts defined make up the Reservoir ravine and canyon, being the most resistant and least easily eroded materials, but also the most permeable, mainly the M4 formation, which is the area where there were important outward filtrations of water from Reservoir Number III.
  6. Quaternary (Q), alluvial and colluvial materials being distinguished in the beds of the rivers and big streams, terraces formed by gravels and sands on the right embankment of the reservoir basin, and the silts filling it as well as other artificial deposits of a different nature.

Geology and Geotechniques of the Storage Area Upstream of the dam and the Downstream Boundary

The detailed study of the downstream boundary of the storage area during the project phase was based on the data and conclusions of the S.G.O.P. report (7/87) regarding to the heightening of the Puentes Dam.

Before carrying out the consolidation injections in the block foundations, permeability tests were made, reaching figures of more than 10 Lugeon units, and even total loss, in certain levels.

The testing campaign carried out during the drafting of the Project included the perforation of five mechanical probings, aligned in a profile transversal to the bed that reached depths of between 40 and 106 m.

The following outlines are a sample of the materials forming the area of the reservoir and the downstream boundary.

Drawing of the geological ground plan of the downstream boundary for the storage area
Geological ground plan of the downstream boundary for the storage area

The Project data were completed with those obtained during the excavations, and through the tests and consolidation injections made during the phase of construction of the New Dam.

Drawing of the lithological column in the area of the Puentes downstream boundary
Lithological column in the area of the Puentes downstream boundary

The morphological characteristics of the downstream boundary for the storage area and surroundings can be summarized in the following points:

  • Downstream from Dam III, the Guadalentín river bed forms a canyon of vertical walls; on its banks there are many artificial deposits (scree and debris from the demolished dam).
  • In the downstream boundary area, the reservoir basin is full of flowing and consolidated silts, deposits that take up more than half the initial capacity of the reservoir of the old dam as a result of the sediments brought by the River Guadalentín, which are of the order of 500,000 m³/año.
  • In the natural downstream boundary for the storage area, below the silts, there is a considerable thickness of debris filling the bottom of the canyon, becoming more and more inserted toward the old dam (Dam III), forming considerable ledges, mainly on the right embankment of the reservoir, where there is also greater subsidence of calcareous blocks.
  • Apart from the silts and the debris defined, the area of the downstream boundary is formed by calcareous-sandy Miocene material toward the roof, and loams on the base dipping about 10º to the East and South-east. These materials are divided into the five main formations (7 in all) of the lithological column that has also been represented on the previous page.

The investigations carried out have determined the following conclusions:

  • The thickness of these lithological units hardly varies throughout the whole downstream boundary.
  • The M4 level of crystalline limestones, which are thicker, are highly permeable, as revealed by the total losses of drilling water.
  • The thickness of the debris on the bottom of the reservoir basin of what has been the new ravine varies between 10 and 20 m, appearing some impervious loams below.
  • The areas of the reservoir basin which are most easily eroded are located to the NW, on the left bank of the River Luchena, to the south of Cerro del Buitre, in the central part of the reservoir, in the area of Cortijo de las Marinas, and on both banks of the River Corneros. This classification means it is advisable to carry out hydrological-forestry corrective plans in the ravines and main rivers that end in the reservoir to limit its silting up.

up

previous next back