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Rodeos Reservoir

History.

The Segura River Basin is, amongst all those in the national territory 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There are historical references since almost five hundred years ago that speak of the disasters suffered in the area due to these meteorological phenomena, including losses of human lives. In the eighties there was a total of eight flood events which caused widespread damage to roads, farms and, most important of all, towns and villages.

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, Luchena.

View of Los Rodeos Dam downstream
View of Los Rodeos Dam downstream

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 Mr. Ramón García and Mr. Luis Gaztelu to mitigate the devastating consequences of the Santa Teresa flood, occurred in 1875. From this period are Fuensanta and Cenajo reservoirs, on the Segura river, Talave and Camarillas reservoirs on the Mundo river; Alfonso XIII Reservoir on the River Quípar, Santomera Reservoir on Rambla Salada, La Cierva Reservoir on 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.

In May 1977 the “General Flood Control Plan of the Segura river Basin” was drawn up.

In July 1984 the “Specifications Sheet of Bases for the Contracting of Technical Collaboration Works in the Study of Los Rodeos Dam Project (Murcia)”.

Excavation of right abutment
Excavation of right abutment

The catastrophic floods suffered by the Community of Valencia and the Region of Murcia in July and October 1986 and 1987, led the Government to promulgating Royal- Decree Law 4/1987 of 13 November (BOE of 14 November 1987) in which urgent measures were adopted for repairing the damages caused by the floods in the aforementioned Autonomous Communities. This Flood Control Plan considered a total of 23 actions in the whole basin, including those of Los Rodeos Dam.

Excavation and initiation of concreting of central blocks
Excavation and initiation of concreting of central blocks

Basing themselves on the preliminary plan for the Flood Control Plan mentioned above, two boundaries for the storage area were studied; the one finally chosen and another upstream from it.

The geological-geotechnical characteristics of both boundaries were similar and the one downstream had a larger dam volume. However, the latter was chosen because the reservoir volume was approximately 5 times greater (15.8 million cubic metres as opposed to 3.3 million cubic metres), the capacity of the upper part of the boundary for the storage area being practically ineffective for flood abatement, which is the basic purpose of the dam.

The choice of dam type was based, in the first place, on excluding, a priori, the solutions of buttress and multiple arch dams, since, as the downstream boundary for the storage area was very open, this would entail a very high cost in formwork and greater difficulty in placing and compacting the concrete.

The alternatives of a roller compacted concrete (RCC) gravity dam and one of loose materials were studied.

The comparison of solutions resulted in the decision that the RCC gravity dam was more economic, which was chosen in the initial project.

Views of the spillway on the downstream face
Views of the spillway on the downstream face

In June 1993 the Directorate-General for Hydraulic Works awarded the contract for carrying out the works to the company Sacyr, S.A..

In December 1993 a “Construction Project Complementary Information” report was drawn up in which the depth of the foundations was justified and the possibility of reducing the convergence of the spillway discharge channel was indicated as well as that of altering the design of the stilling pool.
 

Photo of the irrigation hut and basin
Irrigation hut and basin

The definitive adjudication of the works took place in May 1994, the document verifying readiness for construction being signed in June the same year.

As a result of the Dam Surveillance Report, the small scale test model and the characteristics of the foundations, Amendment I of the Project was requested, which was authorized in December 1995.

Photo view of the dam from upstream
View of the dam from upstream

The alterations regarding the initial project can be divided into three main groups, the most significant ones being mentioned below:

a) Modifications of the dam structure

  • Readjustment of the location of the dam axis, bringing it slightly forward, improving the incidence of the contact of the foundations on both hillsides.
  • Change in the construction procedure, going from compact concrete to conventional concrete, with readjustment of the geometry of the cross-section.

b) Modifications of the spillway and scour outlet.

  • Construction of a spillway of traditional design, as opposed to the one initially projected - stepped, convergent and non-vertical-.
  • Increase in the thickness of the basin slab, also having nominal reinforcement on the foundation rock.
  • Reduction in the scour outlet sections, giving them natural airing, avoiding the placing of suction pads.

c) Other modifications

  • Inclusion of the irrigation canal inlet that flowed on the left bank.
  • Change in the river diversion works (cofferdams and set of tubes on the right bank).
  • Increase in the width of the crest to act as replacement of paths connecting the banks, avoiding the bridge planned for the reservoir basin.

In December 1996 Additional Works Project I was drawn up, being approved in November 2001.

Photo of the Spillway upstream
Spillway upstream

Among the additional works included in the project, it is necessary to highlight the following:

  • Construction of 10 sediment storage dam on the same number of side gullies in order to reduce the silting up of the reservoir.
  • Correction of the Environmental Impact by means of treating both hillsides downstream, with plantations, drip irrigation network and a basin with a capacity for 6,000 m³ of water.
  • Works for surface drainage and protection on service roads and embankments.
  • Demarcation of the reservoir basin by means of ready-mixed concrete boundary marks.
  • External lighting and illumination.
  • Felling and stump extraction in the basin and transfer of plantations of the floodable area to the dam area.

Galleries and wells were discovered when carrying out the clearing works on a hill of the floodable area next to the left abutment of the dam body, which, due to the Quaternary fills of the hill, indicated the possible existence of a paleochannel, and so a flow of upstream-downstream seepage could occur forming a by-pass of the left dam abutment.

This led to a visit and report by the Dam Surveillance Service, and based on this, the drafting of a Project Amendment II was proposed, which was authorized in November 1998, the budget being validated in June 2001.

The actions of this Amendment referred to the waterproofing of the above-mentioned hill and are summarized below:


  • Construction of a cut-off wall to avoid a possible by-pass, in the event of flooding in the paleochannel of the River Mula.
  • Correction of the upstream slope of the hill using waterproof material to achieve its imperviousness.
  • Construction of a filter on the previous surface, by means of the installation of a geotextile with a draining and anti-polluting capacity.
  • Protection of this waterproof surface with a breakwater resistant to any waves that may occur in the reservoir.
  • Filling of the mining galleries with liquid concrete in order to seal them.
  • Reinforcement of the downstream hill filling to improve its stability regarding phenomena of headwater erosion, by means of flows and the substitution of filling materials.
  • Execution of observation wells downstream, for the control of the phreatic level in this area.

The works were completed in October 2000, and provisional acceptance was made in September 2001.
 

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