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Cahora Bassa Construction Project

The first engineering visit to the Cahora Bassa rapids took place in March 1956. The topography of the Zambezi Valley gave the site adequate characteristics to install a hydraulic structure to dam the river for hydroelectric purposes, thus following up ideas advanced at the beginning of the 20th century by the Portuguese scientist Gago Coutinho when he carried out the first cartographic survey of the Zambezi Valley between Tete and Zumbo.

A year later, the Mission for the Promotion and Peopling of the Zambezi (MFPZ) was set up with the aim of systematically surveying the resources of the Zambezi basin, organising plans for their use and development, and drawing up the necessary projects.

Between 1958 and 1961, with the collaboration of Hidrotécnica Portuguesa (HP), preliminary and viability studies were drafted. The General Scheme and Plan were presented as were the summary blueprints of the construction jobs and the planning of the undertakings of greatest interest for the Zambezi region. With the creation of GTZ (Zambezi Working Group), a step forward was taken in drawing up the project and in the decision to build the dam.

In December 1966, HP was contracted to draw up the project for the Cahora Bassa hydroelectric undertaking. The contract to build the dam was signed between the Portuguese state and ZAMCO (Zambeze Consórcio Hidroeléctrico Lda.) in September 1969. That same month, the contract to supply electricity to South Africa was signed with ESKOM.

In February 1970, GPZ (Zambezi Planning Development Office) was set up, and all the powers of MFPZ and GTZ were transferred to it.

In March 1972 the contract to build the electricity transmission lines was awarded, and in May of that year, the provisional diversion of the river was concluded, allowing a start to be made on digging the foundations and building the dam.

The reservoir began to fill up on 5 December 1974 and was concluded up to the elevation of normal operation (NPA - 326 m) in September 1976. It has only reached higher elevations during the floods of March 1978 (327.74 m) and April 2001 (328.18 m). The maximum flood elevation (NMC) is 329 m.

The HVDC electricity transmission lines to South Africa, covering a length of 1,400 Km, were concluded in January 1974, and the generation, conversion and transmission tests were made in steps. The first step entered into commercial operation on 26 March 1977, the second on 16 April 1978, and the third and final step on 22 June 1979.

The dam was built of conventional concrete, formed out of granite aggregate, resulting from crushing rock taken from the excavation of the foundations and the tunnels, and cement produced at the Dondo-Beira cement plant and, to a lesser extent, cement imported from Zimbabwe.

The total volume of material excavated was about 1,500,000 m3, of which about 200,000 was excavated for the dam foundations, and 1,300,000 for the opening of the power stations, the surge shafts, the transformer room, access tunnels, and conduction galleries.

About 600,000 m3 of concrete was used, of which 450,000 was for the construction of the dam, and the rest for building the underground structures.

The total length of the tunnels, galleries and caverns excavated exceeds 2.5 kms.

The central cavern, which houses the five 415 MW generators, the auxiliary services and the operating and cooling systems, is 217m long, 29m wide and 57m high.

The two surge shafts are 242 m and 342 m long, 15 m wide and 18 m high.

The studies were carried out by the technical departments of the MFPZ and of its successor, the GPZ, with the collaboration of other public and private entities, including study and Project companies, universities and independent consultants-

The project designer for the dam was HP - Hidrotécnica Portuguesa, Lisbon.

The building contractor was ZAMCO - Zambeze Consórcio Hidroeléctrico, Lda., which consisted of 15 members associated into specialist groups by job:

  • CEW, for civil engineering work, consisting of CCI (France), the leader of the group, and also Hochtlef AG (Germany); LTA (South Africa); and Shaft Sinkers (Pty) Ltd. (South Africa);
  • GAE, for electricity generating equipment;
  • TSE, for the converter substations; 
  • TL, for the electricity transmission lines.

For much of the work, this consortium hired the services of local, regional and national companies. 

Extrainfo Engenharias