Design and construction

A year later, the Zambezi Promotion and Settlement Mission (MFPZ) was set up, with the aim of making a systematic survey of the resources of the Zambezi Basin, organising plans for making use of them, and drawing up the necessary projects.

Between 1958 and 1961, with the collaboration of HP (Hidrotécnica Portuguesa), preliminary and viability studies were undertaken. The General Scheme and Plans were presented and the summary drafts of undertakings of the greatest interest for the Zambezi region. With the creation of the GTZ (Zambezi Working Group), a step forward was taken in drawing up the project and in deciding to build the dam.

In December 1966, HP was hired to draw up the project for the hydroelectric use of Cahora Bassa. The construction contract was signed between the Portuguese state and the ZAMCO (Zambeze Consórcio Hidroeléctrico Lda) consortium in September 1969. This same month, the contract was signed with ESKOM to supply electricity to South Africa.

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

In March 1972 the contract for building the electricity transmission lines was awarded. In that year, the provisional diversion of the river was concluded, making it possible to dig the foundations and build the dam.

The Cahora Bassa lake began to fill on 5 December 1974 and was completed up to the normal level of operation (326 m) in September 1976. Higher elevations were only reached during the floods of March 1978 (327.74 m) and April 2001 (328.18 m). The maximum flood elevation is 329 m.

The HVDC electricity transmission lines to South Africa, running for a length of 1400 Km, were completed in January 1974. Generation, conversion and transmission tests were undertaken in three levels which entered commercial operation on 26 March 1977 (first level), on 16 April 1978 (second level), and on 22 June 1979 (third and final level).

The dam was built with conventional concrete, formed out of granite aggregates, resulting from crushing the rock removed from digging the foundations and the tunnels, and cement produced at the Dondo-Beira factory 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 were removed for the foundations of the dam and 1,300,000 for opening the power station, the surge shafts, the transformer room, the access tunnels and the operating galleries.

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

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

The power station cavern, which houses the 5 generators, each of 415 MW, the auxiliary services and the operational 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 undertaken by the technical departments of MFPZ and its successor, the GPZ, with the collaboration of other public and private bodies, including studies and projects companies, universities and independent consultants.

The designer of the undertaking was HP - Hidrotécnica Portuguesa, Lisbon.
Address: Edifício HP, Rua da Guiné, Prior Velho, 2685 Sacavém, Telephone +351-219424748, Fax +351-219418665

The building consortium was ZAMCO - Zambeze Consórcio Hidroeléctrico, Lda., which contained 15 associate members in groups specialized by job:

• CEW, for the civil engineering work, consisting of CCI (France), which led the group, Hochtlef AG (Germany); LTA (South Africa); and Shaft Sinkers (Pty) Ltd. (South Africa);
• GAE, for electrical generation equipment;
• TSE, for the converting sub-stations;
• TL, for the electricity transmission lines.

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