Page 22 - CIWA Climate Resilience & Mitigation Assessment

Case Study – Kariba Dam Rehabilitation Project
The outflows into the Zambezi river from the hydroelectric region, with an estimated 3 million people living in the
power stations either side. ©GavinD / iStock
⁴⁰ Hughs and Farinosi. 2020. Journal of Hydrology: Regional Studies. (32) 100763
20 ⁴¹ https://www.zambezicommission.org/sites/default/files/publication_downloads/factsheet_zamcom.pdf
Case Study – Kariba
Dam Rehabilitation
Project
Context
The Zambezi River Basin (ZRB) is the fourth largest
watershed on the African continent, spanning eight
countries in Southern Africa: Angola, Botswana, Malawi,
Mozambique, Namibia, Tanzania, Zambia, and Zimbabwe.
It provides important ecosystem services and livelihoods
to more than 38 million people and is essential for regional
hydropower production and food and water security. The
Zambezi’s hydrological cycle is influenced by strong
climatic and seasonal variations. Periodic droughts and
floods exacerbated by climate change are having
devastating impacts on the region. Climate models and
future projections for the basin indicate that relative
impacts can be quite different across the whole Zambezi
River Basin, the greatest impacts being in the Lake
Malawi/Nyasa sub-system.⁴⁰ According to the Zambezi
Watercourse Commission Secretariat, most climate models
agree that the basin will be warmer and drier, on average,
with more consecutive days without precipitation.⁴¹
The large dams built along the Zambezi River are a
pillar of the region’s energy and water security. They
also help regulate water flows by providing water
storage capacity during drier periods and flood
protection during wetter periods. The Kariba Dam and
HES is the largest hydropower installation on the
Zambezi in terms of installed capacity. It was
constructed between 1956 and 1959, creating the Kariba
Lake in the process, the world’s largest artificial lake by
volume. Located at the border between Zambia and
Zimbabwe, the Kariba Dam HES is jointly operated and
maintained by the two countries under the ZRA.
Electricity is generated via two underground
hydropower stations located on the north bank in
Zambia and the south bank in Zimbabwe, with a
combined installed capacity of 2,130 MW. This
installation is crucial for the power generation of the two
countries and regional economic development. The
power stations account for 37 and 42 percent of Zambia
and Zimbabwe’s total generation capacity, respectively.
After more than 50 years of operation, the Kariba
Dam required a series of time-sensitive rehabilitation
works to prevent further degradation of the structure
that could potentially lead to dam failure. In the first
20 years following dam construction, sustained heavy
spillage episodes resulted in erosion of the bedrock
immediately downstream of the dam foundation,
presenting a risk to the stability and safety of the dam
wall. Moreover, the sluice gates that make up the
spillway were distorted over the years from a chemical
reaction in the concrete, which could prevent effective
management of the reservoir level in case of flood.
Given the large storage volume of Kariba Lake (181 km3),
a dam failure would result in catastrophic flooding in the
potential impact area.