Crevillente Reservoir
Background
Crevillente Channel flows downstream from the headwaters of the same name in the Segura Left Bank Distibution Canal, where this infrastructure crosses Rambla Salada or Abanilla. The flows that it transports are assigned to the Sexta Elevación de Riegos de Levante de la Margen Izquierda del Segura (Segura Left Bank Irrigation Community), in the heart of the Júcar basin, whose first inlet is located at the San Antonio Reservoir in the municipal district of Guardamar del Segura. In the general Preliminary Plan for the main pipelines and regulation works in the South-east of the Joint Exploitation of the Tagus-Segura, Phase I, approved on 1st April 1971, it had been planned that this Canal would end in a siphon 2.5 km long, to directly supply the headwaters of the irrigation areas mentioned, materialized with two 2-metre pipes with a total capacity of 11.4 m³/s. But the need for irrigation during 18 hours a day and the great demand made it necessary to consider the possibility of building a regulating reservoir at the Canal tail-end, near the siphon and in the region of the Barranco del Bosch, in order to store the difference between the incoming flow and that required for irrigation. The morphology of the land on which the reservoir was to be built, together with the associated volume, meant that the only solution possible was to close the natural course by means of a dam. The viability of this project depended on the geological-geotechnical report that had to be drawn up by the Public Works Geological Service (SGOPU).
On 14th April 1971, the Technical Director of the Confederación Hidrográfica del Segura asked this Body for this document, who, in December 1972, issued the Geological Report on the Crevillente Reservoir (Municipal District of Crevillente, Alicante), which informed of the viability of building the above-mentioned reservoir by means of a dam of up to 45 m in height, at the point where the Barranco del Bosch crosses the N-330 Main Road. On 13th March 1973 the Directorate General for Hydraulic Works (DGOH) approved the drafting of the corresponding project.
The Project for the Crevillente (Alicante) Canal Regulating Reservoir was drawn up in September 1974 by the Confederación Hidrográfica del Segura engineer Mr. Alfonso Botía Pantoja, when the main pipeline and regulation works of the Joint Exploitation of the Tagus-Segura, in the Segura basin, were already underway and whose date of completion was due on 31st December 1974. The project considered two possible alternatives for the joint exploitation of the Crevillente Canal-Regulating Reservoir system. In Solution 1, which was the one that was finally chosen, Crevillente Canal would transport the instant flow by gravity to the canals of the irrigable area, and the surpluses would be diverted by pumping to the regulating reservoir created by the Crevillente dam. The height required for the dam was to be 55 m on foundations and the volume of the reservoir approximately 14 million cubic metres. In Solution 2, Crevillente Canal would flow by gravity into the regulating reservoir, where the daily differences between the supply and the demand, which would be supplied directly through the intake from the reservoir, were to be regulated. This different conception of the hydraulic system meant that the height of the dam would have been 29 m and the reservoir would have had a capacity of 1.5 million cubic metres.
The project was approved by DGOH on 12th August 1977, for the purpose of public information. In the same DGOH report, the Confederación Hidrográfica del Segura was given orders to proceed with detaching the project for the diversion of the CN-330 road, so that it could be dealt with separately, as well as to introduce the recommendations and modifications put forward in the report of the Dam Surveillance Service in the dam project. But this project would not be definitive since, during the course of the construction of the dam, it was necessary to issue two Amended Projects and an Additional Project.
As a result of the previous procedure, Amended Project 02/79 of the Crevillente Canal Regulating Reservoir was issued, signed by Mr. Alfonso Botía Pantoja, which fully responded to the indications of the DGOH, separating the road project and negotiating it before the Roads Department, as well as incorporating all the amendments of the Dam Surveillance Service Report.
View downstream from the dam
The specified term for completion was 24 months starting from the date the document verifying readiness for construction was signed. On 4th May 1982, the chief engineer of the works gave a favourable report of the contractor’s proposal to change the dam cross-section from a rockfill dam with an impervious core to a graded aggregrate one, which involved building a greater dam volume and embankments, although the proposal would not entail any increase in the budget. The alleged cause was that the quarries in question could not provide sufficient volume of rockfill and so it would be necessary to turn to other ones further away, which would lead to an increment in the works’ budget. In order to avoid this, a proposal was made to modify the projected section, conserving the core, replacing the shoulder rockfill with graded aggregrate coming from the vicinity of the natural downstream boundary for the storage area, protected with rockfill and extending the downstream filters to the outside.
On 6th June 1982, the DGOH authorized the drafting of Project 05/83 on “Amendment I of the Crevillente Canal Regulating Reservoir”, with an extension in the term of three months, in other words, until 31st December 1984. This project was approved on 24th January 1984. During the execution of the foundation excavation works it was discovered that the loams of the base were highly weathered, which meant that the depth excavated had to be increased, as well as the material required for refill.
In order to calculate the increase in the cost of the increase in the excavations, core, shoulders and concrete for lining the galleries, on 21st May 1984 the DGOH authorized the drafting of Project 09/84 on “Amendment II of the Crevillente Canal Regulating Reservoir”. This project was technically and definitively approved on 21st November 1984, and the term for its completion was extended six months.
View of the spillway on the left abutment.
Project 07/85 on “Additional Work I of the Crevillente Regulating Reservoir” was also drafted with the purpose of carrying out various additional works to improve the functioning and exploitation of the Regulating Reservoir.
The works were completed in March 1986, in compliance with the term finally specified Their provisional acceptance was made on 15th July 1986 and their final acceptance on 22nd July 1987.
Access
The dam is located at the intersection of the former CN-330 main road -connecting Crevillente with Albacete (today the CN-325) - with Barranco del Bosch, in the municipal district of Crevillente, province of Alicante, in the Autonomous Community of Valencia. From Murcia, Crevillente reservoir is reached by the A-7 (E-15) Autopista del Mediterráneo, taking the Crevillente turn-off, going through the town and then taking a diversion to connect with the current N-325 main road. The access to the dam is well-signposted at km 19 of this road. The dam buildings are to be found about two hundred metres later and access to them is along a paved road.
The geographical environment of the reservoir is densely populated and the distance by road from the dam to the most important cities is 1.5 km to Crevillente, 11 km to Elche, 47 km to Murcia and 28 km to Alicante. The nearest railway station and airport are in the city of Alicante.
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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Alicante |
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Municipality
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Crevillente |
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River
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Bosch ravine |
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Hydrographic basin
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Júcar |
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DETAILS OF THE RIVER
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Length of the river
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0,90 Km |
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DETAILS OF THE BASIN
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Surface area of Crevillente reservoir basin
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11,80 km² |
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Maximum altitude of Crevillente reservoir basin
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792 m |
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DETAILS OF CREVILLENTE RESERVOIR
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Shore length
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14,00 km |
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Reservoir surface area
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90,87 ha |
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Reservoir volume
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12,78 hm³ |
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BODY OF THE DAM
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Type
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Loose Materials |
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Materials
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Earth, breakwaters, chippings and clay |
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Upriver slope
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2,35/1 (h/v) |
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Downriver slope
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2,60/1 (h/v) |
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Height above course of river
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54,50 m |
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Level of crest (axis of road)
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147,50 m, |
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Crest length
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360,00 m |
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Crest width
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12,50 m |
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Total volume of concrete
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1.100.000 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 with no floodgates |
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Location
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Left-hand support |
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Position relevant to flow direction
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Lateral |
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Situation
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Left support |
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Total free length
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41,50 m |
Purpose
The function of Crevillente Reservoir is that of regulating part of the flows transported by the Left Bank Distribution Canals to meet the irrigation demands of part of the irrigation community Riegos de Levante de la Margen Izquierda in an area located in the Júcar river basin. Its reduced catchment area and small flow volumes would never have justified the construction of this reservoir that practically acts as a regulating reservoir at the tail-end of the Canal. It is an important piece in the distribution of the water coming from the Tagus-Segura Aqueduct through the Distribution Canals, and so practically all its inflow comes from the Tagus-Segura Joint Exploitation
Crevillente Reservoir is a gravity dam, of a straight ground plan -except in the area of the two abutments where there a slight curvature -, of loose materials with a clay core. The core is the impervious element, and it goes from the foundations to one metre below the crest level. Going from the inside to the outside, the reservoir is formed by the core of clayey loams, two layers of filter material -fine and thick – downstream from the core, two shoulders built with graded aggregate from the area, an outer cradle of gravel, and a layer of rockfill facing. The length of the reservoir on the ground plan is 360 m, its height from the foundations is 58.00 m, being 54.50 m on the bed. The volume of earth used to build the body of the dam was 100,000 m³.
The cross-section of the dam is trapezoidal with an upstream slope of 2.35:1 and a downstream slope of 2.60:1. The crest is 147.50 high and 12.50 m wide.
So as to limit the interstitial pressures during the construction of the dam and when the drawoffs take place, it has a complex system of filters and drains built on both shoulders.
Territorial and Administrative Context
Physical Characteristics of the Basin.
The Crevillente reservoir basin catchment area has a surface area of 11.80 km², its maximum height is 792 masl and it is completely within the municipality of Crevillente. The Barranco del Bosch, in which the reservoir lies, has hardly any flow during the days following significant rainfall. With regard to the latter, is interesting to point out that the rainfall with a return period of 1,000 years generates a peak flow of scarcely 85 m³/s. The Barranco del Bosch basin has no tributaries as such. The surface catchment area has a purely rectangular shape, except for a small fork toward the NW, of about 4 km in a perpendicular direction to the reservoir and about 3 km in a parallel one. This territory receives an average annual rainfall of about 450 mm.
The Normal Maximum Storage Level (MNEN) was established in the original project at the threshold of the overfall spillway and is located on the right embankment of the reservoir. It has a chute and a stilling pool and is situated at a height of 145.00. The total storage volume for the normal maximum level is 12.78 million cubic metres, while the live storage one is slightly reduced to 12.28 million cubic metres. On the other hand, the surface inundated for this level is 90.87 has, the shore is 14 km long and the length of the reservoir 0.9 km upstream.
As for the standard project flood, calculated for a return period of 500 years, the flow is about 75 m³/s, the maximum level reached by the reservoir –the Standard Project Flood Level (NAP) - is 145.52, which corresponds to a storage volume of 13.26 million cubic metres and an inundated surface of 93.03 ha.
View of the reservoir from the right embankment
Geology and Seismology.
Regional Geology.
Crevillente Reservoir is located on posalpídicos sediments, deposited in a predominantly marine atmosphere. These materials lie on the north-eastern edge of the allochthonous Sub-Baetic area and, more specifically, on the eastern end of the Sierra de Crevillente that is formed by an anticline of Triassic, Jurassic and Cretaceous materials, whose WSW-ENE axis dips toward the East below a mighty Miocene series. The materials of the Mesozoic series that appear in the Sierra of Crevillente are gypsiferous loams of Keuper facies, limestones, dolomites and dolomite limestones, loamy limestones and loams.
The Tertiary series begins, discordant, with levels of conglomerate and sandstones (molasses) and continues with loams, clays, poorly-cemented sandstone, limestones and loams, and ending with layers of conglomerate, sandstones and reddish loams from the Pliocene.
The Quaternary series is a recent alluvial one which covers large areas, but outside the zone near the reservoir.
The compact calcareous nature of the Jurassic contrasts with the material loamy- gypsiferous one of the Triassic, which morphologically gives rise to a marked differential erosion that results in high mountain peaks, bordered by deep ravines with vertical walls. In the Aspe valley, this aspect is attenuated by the filling of alluvial materials in the depressions. On both sides of this core there are Tertiary mountainous regions whose differences in level are more moderate, but also quite broken up by differential erosion, with valleys parallel to the structure and consequent collectors, frequently inside faults. These Tertiary materials (Middle Miocene to Upper Pliocene) present frequent lateral variations of related litofacies, both with the immediate local flows and with the various depths of sedimentation.
Geology and Geotechniques of the Storage Area Upstream of the Dam.
All along the bed there is a rapidly decreasing thickness of alluvial material downstream, as it is natural due to the morphology of the bed, because the bed sediment is at its maximum at the narrowing. This thickness ranges from between a maximum of 4 m, to about 2 m and less than one metre. During the phase of the primitive construction project in the year 1972, seven (7) mechanical probings were carried out, with a total length of 600 m drilled and distributed in 3 different profiles; two of them transverse to the ravine and the other one longitudinal. The percentage of core was quite variable in each probing, because some stretches were found in which it was almost 100% and others in which recovery was practically nil. The results of the profiles indicated that the right embankment, in its first metres, was in worse conditions than the left.
In order to evaluate the permeability of the area, water admission tests were carried out, taking as an acceptable limit approximately 4 l/m/minute for an injection pressure of 10 atm.
Total losses were not very frequent, except in one probing, in which, apart from the percentage of core recovery was very irregular, admissions were noticeably greater than in the rest of the probings.
The reservoir basin is completely built on Miocene terrain. It is impervious, since it is in areas downcut by erosion in loams and clays. There are levels of sandstones and limestones that are not very permeable and which are filled with impervious material.
Geology and Geotechniques of the natural downstream boundary for the storage area.
The terrain of the downstream boundary in which the dam is built corresponds to a series of levels of concordant loams, limestones and sandstones that dip 30º and 40º toward the South. All these materials form the south slope of a gentle anticline. During the phase of the primitive construction project in the year 1972, seven (7) mechanical probings were carried out, with a total length of 600 m drilled and distributed in 3 different profiles; two of them transverse to the ravine and the other one longitudinal. In all the probings natural radioactivity tests were carried out. In the final project, when the typology of the dam was changed to that of loose materials with an impervious clay core, the boundary was brought slightly forward upstream and so the geological-geotechnical characterization of the land, on dipping downstream, was critically assumed and confirmed during the execution of the works.
The lithological column that was deduced from the probings is quite similar in all, since it begins with detritic limestones that gradually give way to detritic sandstones and, later on, to progressively less detritic loams. There are some levels of detritic limestones, sandstones or clays at various depths that mean the changes are not abrupt. These levels begin with a series of detritic limestones that gradually give way to detritic loams, appearing in some parts a level of sandstones. Then there is a level of yellowish sandstones, in which a level of light grey clays is inserted. Next can be observed a great layer of loams and detritic loams of about 25 m, and in which some correlations of the levels of sandstones and limestones appear, although, in general, there does not seem to be any continuity of them. Further down, there is a level of detritic yellowish limestones of variable thickness that gives way to a level of clays and dark grey loams. All the probings end with a level of loams of diverse tonalities that start off being detritic and become more clayey as they go down.
Geologically-speaking, no problems were found for the construction of the dam in the natural downstream boundary for the storage area chosen in Amended Project 02/79 of the Crevillente Canal Regulating Reservoir. Finally, the dam was built further upstream in order to adapt the loose-material dam, with a central clay core, to the morphology of the area. The core rests, at least in the central two thirds, on impervious materials formed by more or less clayey loams and, to a lesser extent, on calcareous and sandy loams in, at least, 250 m that the probings went through. They are more than 4 m thick, they dip downstream (concordant with the structure of the area) and their permeability is more than sufficient. On the abutments, the core rests on levels of sandstones and detritic sandy limestones that, since their imperviousness is doubtful, made it necessary for them to be cleaned and their joints sealed.
Plans and Ortophotographs
Plans
(15 MB)Ortophotographs
Situation
Crevillente Reservoir, also known as the Depósito Regulador del Canal de Crevillente (Crevillente Canal Regulating Reservoir), is located in the ravine called Barranco del Bosch. This ravine has a discontinuous, low water flow, and so the flows coming from the basin itself are practically non-existent, its main source of supply being the Crevillente Canal. This Canal flows at a lower level than that of the reservoir and so the water can either continue directly toward the distribution system of the irrigable area or be diverted toward a pumping station that pumps it up to the reservoir for its regulation. The pumping station is located on the left embankment of the Canal, near the foot of the dam, and the pumped flow reaches the reservoir through a reversible inlet that goes through a tunnel beneath the right abutment of the dam.
Crevillente dam and reservoir can be found on the Servicio Geográfico del Ejército Map Number 893 (Elche), on a scale of 1:50 000, published in 1997. The dam closes the Barranco del Bosch, about 6 km upstream from its outlet into the Laguna del Hondo.
The coordinates of the point where the Bosch ravine meets the reservoir comes as follows:
U.T.M. coordinates :
Reference system ETRS89. Time zone= 30
X=693.429
Y=4.236.689
Geographical coordinates (based on the Greenwich meridian):
Longitud 2º 53' 45" West
Latitud 38º 15' 25" North
