The Kariba South power station is a 1,050MW hydroelectric power plant located on the Zambezi River at the Kariba Gorge, in the Mashonaland West province of Zimbabwe. It is currently the biggest power plant by installed capacity in Zimbabwe.
The Kariba South power station was originally developed with six generating units commissioned between 1959 and 1962. The facility was expanded by two additional units of 150MW capacity each in March 2018.
Owned and operated by state-owned Zimbabwe Power Company (ZPC), the Kariba South facility has been the biggest source of domestic electricity supply in power-starved Zimbabwe that relies on electricity imports from other countries including South Africa and Mozambique.
The other major power projects in the country are the 920MW Hwange coal-fired power station which is being expanded to 1,520MW capacity, and the planned Batoka Gorge hydroelectric power project in which Zimbabwe will have a share of 1.2GW generating capacity.
Reduced power output from Kariba South
Although the Kariba South power station typically accounts for more than half of the country’s electricity, low dam water levels due to the prolonged drought in the region since May 2019 has led to trimming down the facility’s electricity output to almost one-fourth of its design capacity as of December 2019.
Location and site details
The Kariba South power plant is located on the south bank of the Kariba Dam, the world’s biggest man-made dam based on water storage capacity. The reservoir created by the dam is called the Kariba Lake that has up to 185 billion cubic metres (bcm) of water storage capacity with a surface area of 5,580km2.
The Kariba Dam is located on the Zambezi River at the Kariba Gorge, on the border of Zambia and Zimbabwe.
The Kariba North power station located on the north bank of the dam belongs to Zambia. The Kariba North power station was originally developed with 720MW of installed capacity, which was expanded to 1,080MW by adding two 180MW units in 2013.
Financing for the Kariba South power plant expansion
The Zimbabwe Power Company (ZPC) launched the £332m ($533m) expansion project to add two 150MW generating units to the Kariba South power station in September 2014. The 300MW expansion facility was commissioned by March 2018.
Of the total £332m ($533m) estimated project cost for the expansion, China Eximbank provided £199m ($320m) under a non-concessional loan agreement signed in 2013, while the remaining £132m ($213m) was borrowed from Development Finance Institutions (DFIs) by Zimbabwe Power Company (ZPC).
Kariba South power plant make-up
The Kariba South plant facility initially comprised an underground powerhouse equipped with six vertical-shaft Francis turbine units. At the time of commissioning during 1959 and 1962, each of the units had a rated capacity of 111MW, which was upgraded to 125MW capacity later.
Water to the underground powerhouse is drawn through a short horizontal intake structure from the Kariba Lake. Operating at a rated head of 86m, the turbines receive high-pressure water flow through vertical penstocks.
The 300MW Kariba South expansion facility comprises two 150MW vertical-axis Francis turbines placed inside a 24m-wide, 36m-high and 94m-long underground powerhouse. The design head for the expansion plant is 89m.
The Kariba South extension also involved the construction of a 25m-diametre and 60m-high surge chamber, two 7m-diametre vertical shafts, two 6.5m-diametre steel-lined penstocks, and a single 12m-diametre tailrace tunnel.
The electricity generated by the Kariba South power station is evacuated into the National grid of Zimbabwe via a 330kV switching station.
Kariba Dam structure
Kariba is a 128m-tall and 620m-long double curvature arch type dam with 14m-thick crest. The Kariba Lake created by the dam is up to 280km-long and 32km-wide.
The Kariba Dam has six 8.8m-wide and 9m-high spillway gates with a discharge capacity of 9500m3/s.
Kariba Dam history
The Kariba Dam project on the Zambezi River was conceived in 1953, the year in which the Central African Federation or the Federation of Rhodesia and Nyasaland was created by Britain.
The Central African Federation comprised Southern Rhodesia (Zimbabwe), Northern Rhodesia (Zambia) and Nyasaland (Malawi).
Construction of the dam was started in 1956 and completed in 1959.
The Central African Federation broke up with Zambia and Malawi gaining independence in 1963, while Zimbabwe was recognised as an independent sovereign country in 1980.
The Central African Power Corporation (CAPCO) was established in 1963 to control power generation and transmission in both Northern and Southern Rhodesia.
CAPCO was dissolved and reconstituted as the Zambezi River Authority (ZRA) through parallel legislation by the Zambia and Zimbabwe governments in the Parliaments of Zambia and Zimbabwe 1987.
ZRA, which is equally owned by the Zambia and Zimbabwe governments, is responsible for the operation and maintenance of the Kariba Dam, as well as for the water allocation to the Kariba North and Kariba South power plants.
Kariba Dam rehabilitation project
The Kariba Dam has been undergoing a £235m ($294m) rehabilitation project since 2017, in order to fix the deformities on the structure that were figured out in a series of assessments.
The Kariba Dam overhaul project involves the reshaping of the plunge pool and the refurbishment of the spillway gates.
The Kariba Dam rehabilitation project is being funded through a combination of grants and loans from European Union, World Bank, African Bank, Government of Sweden, as well as the Zambezi River Authority (ZRA).
Scheduled for completion by 2025, the rehabilitation project is intended to increase the efficiency as well as extend the operational life of the dam, which has been in service for Zimbabwe and Zambia for more than six decades.
Impresit Kariba, a consortium of four Italian companies namely, Impresit, Girola, Lodigiani, and Torno, was the construction contractor for the Kariba Dam that was built during 1956 and 1959.
Impresit, Girola and Lodigiani were later merged to become Impregilo (now Salini Impregilo).
Chinese state-owned Sinohydro was selected as the turnkey engineering, procurement and construction (EPC) contractor for the 300MW Kariba South power plant expansion project in December 2012.
A consortium of GE Hydro France and Freyssinet International, which is a subsidiary of Vinci Construction, was contracted by ZRA for the rehabilitation of the Kariba Dam spillway in May 2019.
Razel-Bec, a subsidiary of French construction and civil engineering company Fayat Group, was engaged for dam safety repair works related to the plunge pool reshaping in February 2017.