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La Risca Reservoir


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.

As a result of the catastrophic floods in the Region of Murcia in the month of October 1973, the “Flood Control Plan of the Segura river Basin” was drawn up. In this document initially no work on the River Moratalla was contemplated.

It was later, once the canalization of the Segura river between Murcia and Guardamar had been analyzed, that the need was recognized for inclusion of defence works on the River Moratalla in the aforementioned Flood Control Plan.

In the Study of Solutions for flood prevention on this river, performed in 1989, the construction of the La Risca reservoir is proposed.

The purpose of the La Risca reservoir is that of flood abatement in this basin, characterized by high intensity rainfall and short concentration times.

By doing this, the peak flow rate is reduced, firstly of the River Moratalla and subsequently of the Segura river after the former flows into it.

The body of the mixed dam is distributed as follows: concrete gravity dam with a straight plan triangular profile on its left abutment and central body, and an earthfill dam on the right abutment. Landslides from the walls of this earthfill dam are prevented upriver by a buttressed wall made of reinforced concrete, and downriver by a wall of reinforced earth. The earthfill dam is completed with a rockfill covering.

The crest in the concrete area is at an altitude of 1,080 metres above sea level, whilst in the earthfill section it rises up to 1,081 metres above sea level. It is 291 metres long, and the slopes in the concrete area have a gradient of 0.75/1 in the upriver face and 0.05/1 in the downriver face; in the earthfill area they have a gradient of 2.5/1 (on both shoulders).

The total height of the concrete dam from foundations to crest is 26.88 metres.

Detail of the concrete dam section type
Cross section of the concrete dam

The dam is divided into different sized blocks; thus, going from the right bank to the left, the following areas can be defined:

  • A 35 metre long stretch which makes up the earthfill dam
  • A block of 9.5 metres, denominated B-6, made of rolled concrete which serves as the joint between the earthfill and the gravity dam.
  • Three 20.00 metre blocks denominated B-4-2, B-2-1 and B-1-3, which encompass the full length of the spillway.
  • Twelve 15.00 metre blocks, blocks B-5 to B-27, odd numbers, with a typical concrete gravity dam section.
  • One 6.50 metre block, block B-29, finishing off the left abutment.

The joints between the concrete blocks were sealed using 0.40 metre PVC strips placed at 0.50 metres from the upriver face.

Detail of La Risca Reservoir Elevation

Detail of La Risca Reservoir Elevation

Detail of La Risca Reservoir Elevation
Detail of La Risca Reservoir Elevation

The triangular profile of the dam ends at the crest with a slightly trapezoidal stretch, which makes the upriver vertical face whilst the downriver face has a gradient of 0.05/1. The total width of the crest is 7.50 metres, achieved by two cantilevers measuring 1.50 metres each.

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