The Sunday Mail
Golden Sibanda
IN a cautious approach to managing the Zambezi River, the Zambezi River Authority (ZRA) has allocated the lowest amount of water on record for power generation at Lake Kariba in 2024 to the two state-owned utilities of Zimbabwe and Zambia to avoid a potential drastic fall in the dam’s water levels.
Lake Kariba, the world’s largest artificial lake and reservoir by volume, lies along the border between Zambia and Zimbabwe, 200 kilometres downstream of Victoria Falls. The lake is designed to operate between the levels 475,50 metres and 488,50m (with 0,70m freeboard) for hydropower generation.
Following two recent successive droughts, the lake water level is decreasing, closing the review period to December 27, 2023 at 477,12m, just under 11,48 percent usable storage, compared to 475,73m (1,66 percent usable storage) recorded on the same date last year.
Allowing the water level to fall below the recommended level would pose many risks, including a situation that makes it impossible to refill the reservoir for many years, which would impact the lake’s many commercial and recreational functions.
Given that there was a late onset of the rainy season in Zimbabwe, a key part of the Zambezi River’s lower catchment area, ZRA may review its allocations to the power utilities in Zimbabwe and Zambia. It is also important to note the bulk of inflows into the giant lake come from the river’s upper catchment the Barotse Flood Plains in Western Zambia, with inflows into Lake Kariba peaking in the later part of the first quarter of each year.
Kariba Dam supplies 2 010 megawatts (MW) of electricity to parts of both Zambia and Zimbabwe and generates 6 400 gigawatt-hours per annum at full capacity.
Apart from electricity, the lake is of significant tourism value for the two countries, providing beautiful vistas, gorgeous sunsets, excellent fishing and boating options, water sports and fantastic peaceful vacations or weekends spent soaking up the sun.
The 1 050MW Kariba South Power Station is strategically important to Zimbabwe from two perspectives — first, as one of the country’s two largest power generation facilities, and second, the nation’s largest source of the cheapest electricity.
Generally, the level of power tariffs in Zimbabwe is a hybrid of Kariba’s low-cost power and the more expensive thermal electricity generated at Hwange, a 1 520MW facility, whose output is often weighed down by aged equipment
State power utility Zesa Holdings earlier commissioned two 300MW generators to improve power supply in the country, where demand can peak at 2 200MW against reliable capacity of just above or below the peak demand level.
ZRA, which manages the affairs of the Zambezi River on behalf of Zimbabwe and Zambia, said on Thursday it had allocated 16 billion cubic metres (BCM) of water to be shared equally between Zimbabwe’s Kariba Hydro Power Company and Zambia’s ZESCO Limited for their power generation operations at Kariba for 2024.
This will be the least amount of water allocated to the utilities on record. The previous lowest water allocation was 20 BCM in 2016, according to ZRA.
Chief executive Engineer Munyaradzi Munodawafa said: “The 2024 water allocation was informed by the 2023/2024 rainfall forecasts made by the Southern Africa Regional Climate Outlook Forum-27 (SARCOF-27) and the corresponding downscaled projections by the national metrological agencies of Zambia and Zimbabwe.”
Eng Munodawafa said the projections showed a high probability of a normal to below-normal 2023/2024 rainfall season for the Kariba lower catchment area and a normal to above normal rainfall season for the Kariba upper catchment area.
“This general outlook is highly influenced by the increasing occurrence of El Niño weather conditions, which are expected to significantly negatively impact the rainfall season in Southern Africa. The 2023/2024 rainfall profile outlook implies a high likelihood of below-normal Zambezi River inflows into Lake Kariba,” he said.
Zimbabwe has previously suffered severe drought episodes in 1991-1992, 1994-1995 and 2002-2003, while the most recent ones, which occurred in 2015-2016 and 2018-2019, explain the critically low water levels in Lake Kariba.
“Hydrological simulations carried out by the authority using the Kariba Inflow Forecasting System that is based on satellite rainfall measurements and numerical weather forecasts, providing short-term and seasonal flow forecasts, considered the high likelihood of a below-average rainfall season, which, in turn, will likely result in below-average inflows into Lake Kariba, thereby negatively impacting the volume of water available for power generation during the year 2024,” Eng Munodawafa said.
Accordingly, Zimbabwe and Zambia have been advised to consider alternative sources of power to complement generation at Kariba to fill any electricity generation deficit that could arise due to the lower water allocation at Kariba for 2024.
Eng Munodawafa said the Zambezi River’s flows monitored at Victoria Falls and Chavuma gauging stations have been lower since the commencement of the 2023/2024 rainfall season.
“Levels at the world’s largest man-made lake continue to recede during this period of the season, mainly due to lower inflows than outflows from Lake Kariba, with isolated fluctuations being observed recently due to sporadic rainfall activity around the lake.
“The 2023/2024 rainfall season performance of the lower Kariba catchment thus far has been poor, resulting in below-normal inflows into Lake Kariba.
“On 27th December 2022, Ume, Sanyati and Gwayi Rivers of the Kariba lower catchment recorded 0m3/s, 53m3/s and 0,2 m3/s, respectively, while on the same date this year (2023), Ume recorded 8 m3/s, Sanyati recorded 53 m3/s and Gwayi recorded 0 m3/s.
“The recorded lake level on 27th December 2023 was 477,12m, with 7,25 BCM or 11,19 percent live storage,” Eng Munodawafa said.
With the two power generation utilities producing power within the confines of their respective water utilisation plans for the year 2023, the ZRA boss stated, the lake is projected to close the year 2023 at 477,23m, with 7,78 BCM of live storage, which translates to 12 percent live storage.
He recommended the highest possible live storage be maintained, going into 2024, as a buffer against the anticipated below-normal inflows.
“Accordingly, the authority continues to engage the two utilities through the weekly Joint Technical Committee meetings to ensure that they continue to adhere to their approved water utilisation and water for power generation to ensure sustainable management of the Kariba reservoir,” he said.
ZRA is a binational organisation mandated to contribute to the economic, industrial and social development of Zambia and Zimbabwe by obtaining the greatest possible benefits from the natural advantages offered by the waters of the Zambezi River.
