Barragens de Ribeiradio e Ermida


Ribeiradio and Ermida dams

  • Final value: Over €100 million.
  • The dams are now fully operational.
Ribeiradio and Ermida dams

The company Ramalho Rosa Cobetar, under a joint-venture arrangement with its parent company FCC Construcción and another Portuguese firm, completed the construction of the Ribeiradio-Ermida hydroelectric facility for EDP. This initiative, with a budget of more than de €100 million, is located on the river Vouga, between the Oliveira de Frades and Sever do Vouga areas of the Viseu and Aveiro districts, respectively.

It consists of two hydro sites: the Ribeiradio area, located upstream, and the Ermida area, downstream.

The Ribeiradio hydro area includes the dam, made of concrete with a gravity profile, with a maximum height of 74 m and 262 m length at the crown, and a width of 9 m at the 112.0 m level. The crown axis of the dam is curved, with a circumference with a radius of 240 m. The spillway is located in the central area of the crown, with an adherent sheet and three gate-controlled spans. The water spilled is restored to the river by means of a roller-bucket. A pipe for the bottom outlet runs along the length of the left bank of the spillway. Immediately afterwards, downstream from the dam, is the power plant, in a circular shaft 22.50 m in diameter and 26.90 m in height, equipped with a single non-reversible generator with 72 MW capacity. The shaft is covered by a building for the unloading, assembly and transport of equipment, which also houses the plant’s auxiliary installations. The plant is powered by a gallery 5.50 m in diameter and a separate intake tower, upstream from the dam and connected to the crown via a concrete walkway. The water is returned immediately downstream from the impact basin at the foot of the dam. The scour outlet of the Ribeiradio dam runs parallel to the left edge of the spillway, mostly consisting of an armoured circular pipe 2.5 m in diameter, running through the dam over a total length of 50.30 m. The Ribeiradio reservoir has a total capacity of nearly 135 hm³.

The Ermida hydro area, located nearly 4 km downstream from the Ribeiradio reservoir, includes a concrete dam with a gravity profile and a straight axis, with a maximum height of 35 m and length of nearly 175 m at the crown level, 4 m wide, located at the 55 level. The spillway is located in the central area, with adherent sheet, and a total width of 55 m, with no gates. The water released is received in a hydraulic jump basin before being returned to the river downstream. A bottom-outlet pipe runs along the right bank of the spillway to regulate the flow. It can also be used as a release device for ecological flows.

Next to the meeting point on the right bank of the dam a power plant has been installed at the foot of the dam. It is basically a reinforced-concrete box measurement equipped with two identical generators, each with a capacity of 3.3 MW. The reservoir created by the dam, with a total capacity of nearly 3 hm³, will enable the flows turbined at the Ribeiradio power plant to be modulated, minimising the variations noted in the flow farther downstream.

The contract also included the construction of the accesses to the dams, with a total length of 2,500 m, as well as restoring at a higher level two road sections that would be submerged, one on the EM569 road, 2,350 m long, and the other on the EN333-3 road, 1,000 m long. Each of these replacements featured the building of a new bridge.