Ferradosa Dam and Pumping System

The project covered the following works:

- Dam;

- Temporary diversion of the river;

- Accesses of some 1.4 km distance with a 7 m long platform including longitudinal drainage (concrete ditch) and transversal drainage (6 hydrological accesses);

- Pumping system between the dam reservoir and the ETA consisting of the following:

- Water inlet tower on the reservoir;

- Pumping station installed inside the tower;

- Channel between the pumping station and the ETA.

The body of the dam consists of a central block with a rectilinear axis on top of which is mounted the overflow system along with two lateral joints with a curvature of 200 m.

Along its 121 m length crown runs a 7.5 m wide roadway, the horizontal surface of which is at an elevation of 531.50. In the body of the dam there are two chambers, the General Drainage Chamber with the foundation drains and the pumping shafts and the Observation Gallery which, together with the previous chamber, is equipped with monitoring instruments including, gauges, three dimensional bases, direct and inverted plumb lines, piezometers and total flow spouts.

The hydrological devices incorporated into the dam include the overflow system, the underwater discharge and the environmental flow discharge. The overflow system, with a maximum evacuation flow of 50.1m3/s comprises of the following downstream:.

- Creager type free discharge block with crest at an elevation of 528.50, separated into two 6.25 m spans, comprising of a column 1 m deep on which the roadway rests;

- Discharge channel on steps above the downstream parapet, 13.5 m long with a 1V:0.8H gradient;

- Bureau of Reclamation Type III energy dissipation basin, 13.5 m wide and 11.9 m long;

- Return channel coated in Reno gabions and cushions.

The Ribeira de Freixo was diverted using two pipes of 1.2 and 1.5 m diameter resting on metallic and BA towers respectively. The sole access to the site connected Freixo de Espada á Cinta ETA over 1 km along the reservoir to the crown of the dam before continuing 220 m up to the dam.

Further information about the project:

- The feeder pipe has a length of 1.20 m and DN 160 mm;

- The pumping station has a flow of 20l/s and a manometric height of 44.3 m;

- The pumps used are GRUNDFOS SB77-4-B.