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Doña Ana reservoir

History.

The Segura River Basin is, amongst all those in Spain 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There are historical references dating back almost five hundred years that speak of the disasters suffered in the area due to these meteorological phenomena, including the loss of human lives.

Doña Ana reservoir

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, the River Luchena.

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

Doña Ana reservoir

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.

The construction of a flood abatement reservoir on the River Pliego had been studied in 1937 by the civil engineer Juan Alcaraz Pavia: the project was called Pablo Iglesias Reservoir. The construction of Doña Ana Reservoir was not envisaged in this study.

Doña Ana reservoir

In May 1977 the “Flood Control Plan of the Segura river Basin” was drawn up. Amongst the most important works included in this Flood Control Plan was Pliego Reservoir though the Doña Ana reservoir was not included.

The impossibility of finding a suitable natural downstream boundary for the storage area on the River Pliego downriver from the confluence with the Rambla de Doña Ana, called for the building of two dams -one on the River Pliego and the other on the Rambla de Doña Ana - to achieve the best possible abatement for the River Pliego floods.

The Project for “Pliego Reservoir” was drawn up in June 1987, including the construction of a dam on the Rambla de Doña Ana wadi, as an additional closure point to Pliego Reservoir. The Reservoir is named after the wadi, Doña Ana Reservoir.

Initially two sites were identified for the possible closure point of the dam.

Site 1 was about 1,500 m from site 2, which was eventually chosen, and it was located at the start of a stretch of enclosed valley, between a hill stretched out in the direction of the riverbed on the right bank and a large alluvial terrace with considerable thickness of detritic material on the left bank.

The substrate was made up of a formation of greenish loams on both banks.

Doña Ana reservoir

The left bank was characterized by the presence of a great deal of alluvial deposits and colluvial soils of a thick detritic and permeable nature. In the deposits of fine materials there was intense gully erosion, as well as a system of open joints parallel to the riverbed which provoked slab collapse.

The proposed downstream boundary offered a useful height limited to 6 or 8 m and a length at the crest of 150 to 200 m. The left bank rested on highly permeable alluvial deposits.

Site 2, was located about 1,500 m upriver from site 1, in an enclosed stretch of valley between two elongated hills in the direction of the riverbed and formed from an alternation of micritic limestone, clayey limestone and calcareous shale, with a course transversal to the riverbed and a dip of 15º to 20º downriver.

At this downstream boundary mechanical 15 and 18 m test drillings were performed in order to get continuous samples and Lugeon type permeability tests.

Doña Ana reservoir

From the preliminary studies it was concluded that rock behaviour of the support formation guaranteed its carrying capacity, and that there would be no settling with the load necessary for a 20 or 30 m dam. Thus Site 2 was considered to be suitable for the downstream boundary of the reservoir.

The contract for Pliego Reservoir works project, including Doña Ana Dam, was awarded by public tendering and by Council of Ministers agreement on 14th October 1988, with a completion deadline of 36 months.

Doña Ana reservoir

The Variation Order was signed on the 21st November 1988.

While the works were being carried out, the decision was taken to perform a series of changes with regard to what had been established in the project, amongst which was a new design of Doña Ana Dam with the following modifications:

  • New design for the two height overfall spillway (Rambla del Moro type), increasing drainage capacity.
  • Use of SR type sulphate resistant cement given the chemical characteristics of the water in the Rambla de Doña Ana.
  • Withdrawal of the scour outlet sluice gates, converting the dam into a “hole dam”.
  • Elimination of the planned right of way across the dam’s crest.
  • Deeper foundations for the dam abutments.

In February 1993 the Project for Additional Works I for the Pliego Dam was drawn up which included an electrical connection for Doña Ana Dam.

 

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