Understanding Low Water Levels in Lake Kariba and Their Impact on Electricity Generation

John Cassim

Harare, Zimbabwe – News reports often express concern about low water levels in Lake Kariba. Sometimes, these reports lead to misconception about Zambia and Zimbabwe’s capacity to produce electricity yet Lake Kariba has water. The two countries share the Zambezi River and Lake Kariba, managed by the Zambezi River Authority a Bi-National organization.

While low water levels can affect electricity generation, ConserveZim aims to clarify misconceptions regarding lake water levels and “dead storage.

A bar graph made by Julius Ai using own datasets from monthly updates provided by the Zambezi River Authority. @John Cassim

Live Storage vs. Dead Storage at Kariba Dam

The water used for power generation at the two Kariba power stations by ZESCO and ZETDC comes from intakes located near the dam wall within the reservoir.

The location of these intakes creates two zones in the reservoir based on their height relative to the reservoir base:

  • Dead Storage: Water below the intake level cannot flow into the intakes and is therefore unavailable for power generation.
  • Live Storage: Water above the intake level can flow into the power stations through the intakes and be used for electricity generation.

Even when Live Storage is depleted, Dead Storage may still exist in the reservoir.

A line graph made by Julius Ai using own datasets from monthly updates provided by the Zambezi River Authority. @John Cassim

Lake Kariba’s Capacity and Storage

At full capacity, the Kariba Dam Reservoir can store 181 billion cubic meters (BCM) of water. Of this total, 116 BCM is Dead Storage, and 65 BCM is Live Storage. Dead Storage remains constant, while the maximum Live Storage is 65 BCM.

The actual Live Storage volume fluctuates due to several factors, including:

  • Rainfall: Rainfall amounts affect the level and volume of water flowing into the lake from the Zambezi River.
  • Evaporation: Evaporation from the lake’s surface reduces water volume.
  • Power generation needs: The two power stations utilize the available Live Storage for electricity generation.

These factors influence the amount of usable Live Storage in Lake Kariba.

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