Access

Puentes Dam IV is located at the confluence of the rivers Luchena and Vélez, which, in turn form the river Guadalentín. The latter is a tributary of the Segura on the right bank.

The dam is located about 12 km (as the crow flies) to the NW of Lorca (province of Murcia). The distance from Murcia to the reservoir is about 80 km.

The access to the Puentes Reservoir facilities from Murcia is along the 340 or E-15 main road from Murcia to Almería. On arriving at Lorca there are two possible ways to reach Puentes: one on each bank of the River Guadalentín (plans are under way for a direct access between the Lorca by-pass at the turn-off in the centre of Caravaca de la Cruz that will connect with the access road to the dam on the left bank). The two access roads are connected to each other between Lorca and the dam by a road that fords the Guadalentín.

The access on the right bank begins in Lorca, once the stone bridge over the Guadalentín has been crossed along MU-701 road toward Baños de Fuensanta and La Parroquia: about 11 km upstream from the bridge there is a turn-off, to the North, the access road to the dam, which is reached about 4 km later.

The access on the left bank, also from Lorca, is made by going toward Caravaca de la Cruz: near Lorca, after about 50 m, take a turn-off to the left, which will take you to access road passing over the Main Road.

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

Characteristics

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Situación de la presa de Puentes

Purpose

The new Puentes dam created a regulating reservoir for mitigating the effects of droughts and floods that characterize the hydrology of the region.

General ground plan of the reservoir

The purpose of the reservoir works for the New Puentes Dam was to achieve the following objectives:

• Control the overflows of the River Guadalentín in order to maintain an appropriate level of protection, substantially better than the pre-existing one, of the potentially floodable areas downstream.
• Regulate the resources of the catchment basin intercepted to maintain or improve Lorca irrigation.
• Establish appropriate organs of evacuation to reduce the silting up of the reservoir.

The Guadalentín, a tributary of the Segura, is a river with a very irregular flow rate that can go from being totally dry to producing immense flooding.

Over the last 130 years, it is necessary to remember, amongst others, the following floods:

• October 1879 (Santa Teresa Flood): in Lorca, a peak flow of 1,510 m³/s occurred, causing 13 deaths and considerable damages.
• September 1891 (San Jacinto Flood): greater than the previous one, and thanks to the existence of the Puentes reservoir, located at basin headwaters, the district avoided an unprecedented catastrophe.
• June 1900 (San Aniceto Flood): greater than that of Santa Teresa, which flooded the district of San Cristobal in Lorca.
• October 1948: the estimated flow at the bridge of the Murcia-Granada road was more than 800 m³/s.
• October 1973: according to a report by the Centre for Hydrographical Studies, the maximum flow downstream from Puentes reservoir reached 2,000 m³/s, while El Paretón channel (located in the middle area of the basin) reached about 1,500 m³/s.

Another characteristic of this river is the great amount of solids in suspension carried by its waters, causing problems of silting up, which is reflected in its name in Arabic that means “river of mud”.

Bearing in mind these characteristics of the Guadalentín, there have been many actions undertaken in the past attempting to palliate, as much as possible, the harmful effects of its flooding. Amongst them, it is necessary to mention:

• The Puentes dams are situated in the confluence of the rivers Vélez and Luchena, headwaters of the basin, and where the maximum intensities of rainfall occur, the former being the main cause of great historical floods, such as that of October 1973. The old dam, located downstream from the new Puentes dam, was built at the end of the last century to deal with the demand for irrigation and it was out of use whilst the new dam was being built.
• The Puentes dams play an important role in flood protection. In 1973, before the new Puentes dam was built, the old reservoir overflowed its crest, revealing the need to heighten it, or, as was the case, the need to build a new dam on that site in order to create a reservoir with greater capacity.
• Upstream from Puentes, and on the River Luchena, is Valdeinfierno Reservoir, which, in spite of having been heightened, is currently almost completely silted up and practically without the capacity for regulation.
• Downstream from Puentes Dam, is El Paretón by-pass channel, designed to take part of the flood-waters from the River Guadalentín directly to the sea. Designed at the beginning of the 20th century with an approximate capacity of about 200 m³/s, it has since been enlarged, and in 1973, after the flood, its capacity was increased to 600 m³/s.
• Another recent work designed to control the Guadalentín flood-waters is José Bautista Martín Reservoir, built as part of the General Flood Control Plan of the Segura River Basin and which is situated in the municipal district of Librilla.
• Another essential part of the hydraulic network of the Guadalentín River Basin is the Rambla de Algeciras dam, built on this tributary on the left bank of the Guadalentín, which flows, in its lower part, along the boundary of the municipal districts of Librilla and Alhama de Murcia. With a reservoir capacity of 44.6 million cubic metres, it has a double mission: on the one hand, it is an intermediate storage reservoir of the Tagus-Segura Distribution Canals, and on the other, it was designed as an important flood-control reservoir for the flood-waters of the catchment basin, being built as part of the General Flood Control Plan of the Segura River Basin.
• Lastly, there is an old artificial channel (built before 1651, at the time of the historical San Calixto Flood), in the lower part, to divert the waters from the Guadalentín and to avoid their flowing through the city of Murcia. It is called El Reguerón. Its maximum capacity is considered to be about 250 m³/s, although at some points it can overflow with lower flows.
• The overflows of El Reguerón channel affect the vegas of Alcantarilla and Murcia.

Territorial and Administrative Context

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.

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.

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.

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.

Planos

• Geographical (900 KB)
• Cross-section (259 KB)

Ortofotos

• Presa del embalse (6,8 MB)
• Vaso del embalse (6,8 MB)

Situation

Puentes IV dam is located at the confluence of the rivers Luchena and Vélez, which, in turn, form the River Guadalentín. The latter is a tributary of the Segura river on the right bank.

The dam is about 12 km (as the crow flies) to the NW of Lorca (province of Murcia). From Murcia to the reservoir there is a distance of about 80 km.

Currently the reservoir works and access roads are the property of the Directorate-General for Waters, belonging to the Ministry of Agriculture, Foodd and Environment, and the Segura Hydrographic Confederation is in charge of their operation.

The coordinates of the point where the river meets the reservoir based on Greenwich meridian are as follows::

X 1° 49' 5 " West
Y 37 ° 44' 9 " North

U.T.M. coordinates :

Reference system ETRS89. Time zone= 30
X=604.040
Y=4.177.041