Alto Lindoso Dam

The Alto Lindoso Hydroelectric Power Station is comprised essentially of:

- The concrete dam of the double curved dome type with a maximum height of 110 m and a volume of 510 000 m³ extending along the 297 m top and equipped with two depth discharges;

- Two 9 m diameter tunnel flood spillways with a capacity of 2770 m³/s and fitted with 6 segment type sluices;

- Two independent water intakes, one for each generating unit, equipped with wagon gates and incorporated into two concrete intake towers, each 8.7 m in diameter and 90 m high;

- Two headrace tunnels and two pressure shafts, with a total length of approximately 500 m per unit and a diameter of approximately 5.5 m;

- A spherical valve chamber located at the bottom of the pressure shafts, just upstream of the powerhouse, housing two valves weighing 250 t each;

- An underground powerhouse measuring 20.85 x 91 m² with the main floor at elevation 27.00, a plan area of 91 x 21 and a height of some 40 m;

- Two ´Francis` turbine generators are installed in the powerhouse, each with a power of 350 MVA and a maximum drop of 281 m;

- A busbar shaft connecting the powerhouse to the surface, 350 m high and 6.80 m in diameter;

- A butterfly valve chamber downstream of the powerhouse;

- A surge tank with the following elements; main shaft 65 m high and 21 m in diameter; a surge tank feeder tunnel, 380 m long and 9.50 m in diameter; an expansion chamber 300 m long and 12 m in diameter;

- The storage capacity of the main shaft and associated chambers is approximately 84 000 m³;

- A tailrace tunnel with a length of 5070 m and a diameter of 8.3 m;

- A 18 KV / 400 KV substation.

The tailrace tunnel should also be referred to due to its size and complexity. Such process included:

- A tunnel 5070 m in length and 8.3 m in diameter as stated above with only two adit tunnels corresponding to a cross-sectional area of 53 m²;

- The execution of these works, which involved the pouring of 180 000 m³ of concrete, 1700 t of reinforcement steel and 132 000 m² of formwork, was carried out over a period of approximately 16 months under continuous operation;

- The construction of this structure required the fabrication of a 60 m-long telescopic steel formwork traveller, 8.30 m in diameter, equipped with a self-propelled movement system and weighing approximately 300 t;

- Through the use of this formwork traveller, together with the optimisation of concrete production, transport and placement processes, it was possible to achieve weekly advances of up to 115 m, with concrete placement rates of approximately 35 m³/hour on a continuous 24-hour basis.