Cárcabo Reservoir
Background
After the catastrophic floods which the Region of Murcia suffered in the month of October 1973 the “Flood Control Plan of the Segura river Basin” began to be drawn up. On 24th November 1974 the drafting of this “Flood Control Plan of the Segura river Basin” was finished, and it was approved on 9th December of the same year.
One of the works included in the above mentioned Flood Control Plan was El Cárcabo dam, on the wadi of the same name.
In December 1986 the Rules of Tender for the contracts for the technical studies of El Cárcabo Reservoir (Murcia) were drafted.
As a result of the floods in the regions of Murcia and Valencia in July and October of 1986 and November 1987, the Government enacted the Royal Decree 4/1987 of 13 November (State Bulletin 14-11-87) in which emergency measures were taken, to repair the damage caused by the floods in the Autonomous Communities mentioned. El Cárcabo Reservoir is in Annex I “Planned Programme for Execution of the Works”, works which were to be performed between the years of 1990 and 1992.
Because of everything that has been stated above, on the 23rd December 1987, the Directorate-General for Hydraulic Works decided to adjudicate the work of drafting up the Project for the construction of El Cárcabo dam.
On the 12th June 1989 the Ministry of Public Works and Town Planning decided to technically and finally pass this Project. The Directorate-General for Hydraulic Works decided to adjudicate the tendering performed for the contracting of the works, with the subsequent Variation Order being signed on the 13th November 1989.
The works began on the 14th November 1989, with an official completion deadline of the 14th November 1991.
In February 1991 the Chief Engineer for the Works requested authorization for the drafting of Amendment I to the Project.
The basic reasons alleged for the drafting of this Amendment I to the Project were:
- Change in the type of concrete to be used (following the recommendations of the study 06/89 of the Ministry’s Dam Surveillance Service).
- Change the design for the spillway stilling basin.
- Withdrawal of a service lift which had been included initially.
- Fitting out of the tunnels and the joint of the dam and abutment foundations.
- Change the sloping access ramp to the floodgate chamber for a vertical well.
The technical and final approval for this project was passed on the 1st October 1991 by the Directorate-General for Hydraulic Works, and was financially approved, at no extra cost, on the 23rd December of the same year. In this resolution the deadline was extended by eight months from the date of financial approval, thus the new completion deadline was established as the 23rd August 1992.
On the 13th January 1992 work was resumed on the works which had been paralyzed since the 3rd April 1991 in accordance with the Partial Temporary Suspension Act.
During construction of those works which had not been temporarily suspended, contained in Amendment I to the Project, a series of additional works necessary were highlighted to be able to improve the future services which the Reservoir would provide.
On the 25th November 1991 the Directorate-General for Hydraulic Works authorized the drafting of the Project for Additional Works I which was finally passed by Resolution of the aforementioned Directorate-General on 27th May 1992
The following Works were included in the Project for Additional Works I:
- Fitting the Dam’s left abutment with a crest.
- Installation of ventilation and drainage pump systems.
- Supplementary installation of a generator.
- Lighting of the dam’s crest.
- Access via stairs to the second stilling basin.
- Reinforcement and improvement of the access to the floodgate chamber.
- Safety protection in the gaps and intersections of wells with tunnels and of homes for the dam maintenance team.
In July 1994 both the dam works and the additional works were provisionally handed over. The settlement project, dated July 1994, included the works corresponding to the Amendment I to the Project and the Project for Additional Works I.
Access
Access to the dam and the reservoir
The reservoir can be accessed via the A-30 Motorway to the town of Cieza. From this town one takes the C-330 road, from which after about 3 km another road branches off; owned by the Confederación hidrográfica del Segura which joins the MU-552 passing along the crest of the Alfonso XIII dam.
From this road owned by the Confederación hidrográfica del Segura, after about 9 km, between the turning towards Almadenes and the Alfonso XIII dam, there is a reasonably straight, well defined, surfaced forest track, which after about 2 km reaches the left abutment of the dam.
This road runs along the left bank until the crest. It is made up of an artificial graded aggregate and double surfacing treatment. It is 5.00 m wide and has a hard shoulder surfaced with concrete.
Access road to El Cárcabo Reservoir from Cieza
It can also be accessed from the town of Calasparra via the MU-552 road which connects Calasparra to Mula. From this road the track owned by the Confederación hidrográfica del Segura mentioned in the previous section branches off and which after passing along the crest of the Alfonso XIII dam reaches the surfaced forest track which in turn reaches the left abutment of the dam.
The location of the reservoir can be seen in the following map:
Characteristics
|
LOCATION OF THE RESERVOIR
|
|
|---|---|
| Province | Murcia |
| Municipality | Cieza |
| River | Rambla del Cárcabo |
| Hydrographic basin | Segura |
|
DETAILS OF THE BASIN
|
|
| Surface area of the Carcabo reservoir basin | 36,01 km² |
| Shore length | 9,09 km |
|---|---|
| Reservoir surface area | 7,81 ha |
| Reservoir volume | 0,50 hm³ |
|
BODY OF THE DAM
|
|
|---|---|
| Type | Gravity |
| Materials | Mass concrete |
| Upriver slope | 0,10/1 (h/v) |
| Downriver slope | 0,75/1 (h/v) |
| Height above course of river | 36,00 m |
| Level of crest | 259,87 m |
| Crest length | 118,00 m |
| Crest width | 5,40 m |
| Total volume of concrete | 50.400 m³ |
|
SPILLWAY
|
|
| Number of Spillways | 1 |
| Type of spillway | Fixed lip |
| Location | Centre of the dam |
| Position relevant to flow direction | Frontal |
| Situation | On dam |
| Number of openings | 1 |
| Free length of each opening | 15 m |
| Total free length | 15 m |
| Floodgate type | |
Imágenes
Camino de acceso a la presa de El Cárcabo desde Cieza
Purpose
Phenomena such as torrential rain and floods are not unusual in the Segura river Basin. The damage caused by the water has historically always been a worry for local residents both because of economic losses and the losses of human lives.
In response to this situation, and as a result of the catastrophic floods in the Region of Murcia in the month of October 1973, in 1977 the “Flood Control Plan of the Segura river Basin” was drawn up under the supervision of the then Chief Engineer of the Operations Department José Bautista Martín. This Plan included, amongst other works, a flood abatement dam on El Cárcabo wadi. The purpose of El Cárcabo dam is that of preventing floods in this basin, characterized by some episodes of very intense rainfall during very short periods of time.
The specific aim of this dam is to reduce the flow circulating in the Segura river in the Almadenes-Murcia stretch during flood periods.
Territorial and Administrative Context
Physical Characteristics of the Basin.
The El Cárcabo wadi basin is practically defined by the Alto del Almorchón, to the West, and the Alto de Higuera and the Herrada to the East. The wadi riverbed starts in Puntal del Ripión (580 masl) and runs 8.5 km until it reaches the site of the dam (10 km until its outlet into the Segura river). The average gradient of the wadi is of 3.8%.
Environmental information.
There are two protection orders which include El Cárcabo Reservoir. They are the Special Protection Area for Birds (SPA) called Sierra del Molino, Embalse del Quípar y Llanos del Cagitán, and the Site of Community Importance (SIC), called Sierras y Vega Alta del Segura y Río Benamor. .
Geology and seismology.
Regional geology.
El Cárcabo Reservoir is located in the most northern part of the Baetic Mountains, which in turn is in the north-western segment of the Alpine Perimediterranean Orogenic Belt (alignment of mountain chains with sliding stratum structure originating from the Cretaceous and Tertiary periods which are arranged centrifugally with respect to the sea; Martín Algarra, 1987).
Schematic Division of the Alpine Perimediterranean Orogenic Belt
Within the Baetic Mountains, the area in question is considered as being in the external areas or South Iberian Domain. The materials in this domain occupy a large extent of the belt and represent a time period which goes from the Triassic to the Miocene epoch. They have a structure characterized by a general detachment between the base (Hercynian Paleozoic) and the deformed covering (Mesozoic and Cenozoic folds, faults and buckled strata), where the clayish-evaporitic Triassic level acts as the detachment material and the buckled strata are generally inclined towards the W and NW. The Palaeozoic base. does not outcrop, remaining at a depth of 5-8 km and made up of materials analogous to the Iberian Massif.
General Geological Map of the Baetic Mountains
In addition to this, materials which are autochthonous to the area of our study can be distinguished: those materials which correspond to the pre-mantle formations (Miocene epoch) and those formations made up of post-Orogenic materials which were deposited after the placement of the allochtonous units and which make up the tertiary and quaternary covers.
Geology and Geotechniques of the Storage Area Upstream
This area is, for the most part, made up of Miocene materials, more specifically from the Tortonian period, made up of dark grey loams and loamy limestones (Msb) with gypsum, which can be found in the course of the ravines and below some whitish sandy loams (Ms). The dip is almost horizontal. The quaternary is made up of colluvial materials (pieces of conglomerates, sandstones and limestones mixed with clayey and silty sand), alluvials (formed from limestone and loamy limestone pebbles) and elluvio-colluvials (formed from sandy silt with pebbles). There is a wide strip of allochtonous material which has an average width of 400 m and which crosses the central part of the reservoir from West to East, proceeding from successive Internal SubBaetic sliding strata. These materials are from the Keuper Triassic (motley loams with gypsum and sandstones) and the Eocene (loams, sandstones and nummulite limestones). As far as the geotechnical characteristics of the materials which can be found in the reservoir area the following can be said:
- All of the materials (with the exception of the thick quaternaries), both autochthonous and allochtonous, are practically impermeable.
- The presence of gypsum contributes to the salinity and aggressiveness of the waters.
- The materials are extremely subject to erosion, especially in the whitish sandy loams of the Upper Miocene; as well as to a lesser extent, in the red and green loams of the Upper Miocene and those existing in the Eocene and Triassic
Geology and Geotechniques of the natural downstream boundary
The downstream boundary is located in a very craggy mountain ridge which the El Cárcabo wadi cuts across perpendicularly.
This ridge is 6 km long and 160 m wide as the wadi crosses it and widens out at both ends. There is a 25 m difference in height between one side of the pass and the other formed between the two crags, which the wadi overcomes with a steep gradient and three waterfalls. The first is at the entrance to the pass with a drop of 2.5 m, the second is 25 metres downriver with a drop of 7 m and the third, after a steep stretch enclosed by the last crag has a drop of 10 m as it leaves the last crag. After this last waterfall there is a 4.5 m deep pool.
As a whole the materials of the downstream boundary are conglomerates interspersed with sandstones, sands and clays, which means that there is typical differential erosion, making thick crags from the conglomerates with almost vertical drops, especially on the right bank; and the interspersal of sands and clays produce topographical depressions located between the crags.
On the right bank there are three crags and two depressions; on the left bank five crags and four depressions, the biggest and thickest of these crags being that which is located downriver. Transversally to the riverbed, at the downstream boundary, steep hills appear as soon as we move away from the stream. Most of the sunken areas are covered by a piedmont made up of pieces of conglomerates of different sizes and shapes, which have a clayey sandy matrix and a thickness which varies from several cm to 2-3 metres.
The materials from the downstream boundary are from the Cretaceous era, made up in general from polygenic conglomerates originating from limestone, silica, loamy limestone and sandstone, with a calcareous or sandstone matrix. The conglomerates include lenses of variable length and width of thick grained sandstone, with rich concentrations of carbonates and Lamellibranchia remains, as well as lenses of greenish, white and black coloured, fine grained micaceous sandstones. Green and red clays are also interspersed. The materials at the downstream boundary appear at approximately N-70 with a 75º dip northwards, which makes the crags look vertical. On the wadi riverbed and nearby there are large blocks of conglomerates reaching weights of several tonnes which have fallen off the crags. The alluvial which can be found at the downstream boundary is of little extension and strength.
Seismology.
The seismic hazard differs depending on the place tested and it is standard practice to classify the land depending on this hazard. Following the criteria set out in the “Reservoir Safety Technical Guide. Geological and Prospecting Studies” published by the Spanish National Committee on Large Dams (SNACOLD) in section 3.3 these are classified in three main groups:
a) Areas of low seismicity ba < 0.04g
b) Areas of medium seismicity 0.04g < ba < 0.13g
c) Areas of high seismicity 0.13g < ba where ba refers to the area’s basic acceleration.
Following this classification, El Cárcabo reservoir is located in an area which we could classify as being of medium seismicity, as the basic acceleration for the Municipality of Calasparra is of 0.07g and for the Municipality of Cieza is of 0.09 g.
(3,2 MB)Situation
El Cárcabo wadi is located on the right bank of the Segura river, in its central stretch. It collects the rainfall from a relatively small basin, but which can occasionally register quite significant flows.
El Cárcabo reservoir is in the Municipality of Cieza, between the towns of Calasparra and Cieza.
The reservoir associated with El Cárcabo dam and its surroundings are located within the Segura river Basin, in the Region of Murcia, to the North of the Autonomous Community.
The dam is located on the natural riverbed called El Cárcabo wadi, a tributary of the Segura river on its right bank. The river basin’s morphology is particularly gullied, with the gorge formed by the waters at the rocky cresting called Alto de la Higuera, standing out in particular. Here, there are some vertical crags which have been bored through to produce a series of waterfalls. The dam is located at the natural downstream boundary for the storage area of this valley formed by these crags.
The dam is barely a kilometre away from the outlet of the wadi into the Segura river, upriver from the town of Cieza.
The intersection of the axis of the dam with the riverbed is at the point indicated by the following geographical coordinates, referring to the Greenwich Meridian in the geographical coordinates and zone 30 in the UTM:
Y 1º 31´29" East
X 38º 13' 21" North
Reference system ETRS89. Time zone= 30
X=629.002
Y=4.231.400
