Lake Kariba water level expected to improve
Water levels in Lake Kariba which had dropped for the first time in more than half a century since the reservoir was commissioned to generate power in the 1950s, are expected to improve significantly after climate experts forecast that Zimbabwe and Zambia will receive good rains in the 2016–2017 cropping season.
However, water experts caution full recovery will not be immediate and will require at least three years with sufficient rains.
Zambezi River Authority chief executive officer, Engineer Munyaradzi Munodawafa, told the Zimpapers Syndication Services that the good rainfall forecast for the approaching season offers a glimmer of hope for water inflows into Lake Kariba which generates power for Zimbabwe and Zambia and supports livelihoods in eight Sadc riparian states.
“The latest rainfall forecast is quite positive indeed, but water for generation is very scarce and as a result even if we get above normal rainfall, water recovery at the lake will not be immediate,” said Eng Munodawafa.
Lake Kariba, the world’s biggest man made reservoir, holds around 19 billion cubic metres of generation water compared to the full capacity of 65 billion cubic metres. The lake is approximately 29 percent full. “The estimated time needed for recovery is up to three years,” Eng Munodawafa said.
The Meteorological Services Department issued out the national forecast recently which showed that during the approaching rainy season, which is expected to start this month, Zimbabwe will receive normal to above normal rains bringing relief to the country which has been craving for some good rainfall activity after it was ravaged by one of the worst droughts in decades.
Climate experts say there is a high likelihood of an early start of the season for the whole country.
In the first half of the season (October–December 2016) Region 1 which covers Harare, much of Mashonaland East, Mashonaland West , Mashonaland Central, northeastern parts of Midlands, parts Manicaland and Region 2 which includes the bulk of Matabeleland North, parts of Midlands and parts of Mashonaland West are likely to receive normal to above normal rainfall.
In the same period, the most rain deficit pocket of the country - Region 3 which covers Masvingo, the bulk of Midlands, the extreme southern parts of Manicaland and the bulk of Matabeleland South is also expected to get normal to above normal rainfall.
Good rains are also expected to persist in Region 1 and 2 in the January to March 2017 season while Region 3 is expected to get normal to below normal rains in the same period.
Improved rainfall forecast in parts of Angola and Zambia in the coming season are also expected to increase Kariba Dam water levels.
The Zambezi River Authority says at least 18 percent of the water that flows into Lake Kariba comes from Angola and the western part of Zambia, particularly the Lukulu area.
Lake Kariba straddles Zimbabwe’s border with Zambia, generating hydropower for both southern African countries, but falling water levels have forced the two nations to cut power production.
A drought which ravaged Zimbabwe and Zambia including most other Sadc countries in the 20152016 season, forced the two countries to introduce a punishing load-shedding schedule for consumers.
Before power imports increased, Zimbabwean consumers used to go for an average of 18 hours without electricity due to reduced water levels at Kariba which led to the Zambezi River Authority (ZRA) forcing the Zimbabwe Power Company and Zesco (Zambian) to reduce generating capacity at the Kariba Power Station.
When water levels dropped sharply, ZRA forced the two utilities to reduce power generation to a combined 550MW.
ZRA has allocated an average of 20 billion cubic metres to Kariba South and Kariba North power stations from Lake Kariba for 2016 which the two countries are sharing equally.
The authority is strictly monitoring the two power utilities to continue to adhere to the 550 MW combined generation to sustain the water available until the next rainy season.
By July, the two stations run by the two countries were each given 3,08 billion cubic metres and 1,58 billion cubic metres respectively, of water to be utilised in the remaining five months to year end, according to a report submitted to the Zimbabwe finance ministry.
“It is therefore clear that continued over-utilisation of water by both power stations will negatively impact on the volume of stored water at the end of the year,” said Finance and Economic Development Minister, Patrick Chinamasa, in his recent mid-term fiscal policy review statement.
“Depending on the rainfall to be received in 2017, this may also subsequently impact on the volume of water available for power generation in 2017. Given the uncertainties of long term climate forecasts, it is critical that sustainable utilisation of water at Lake Kariba is prioritised to ensure the reservoir level at the end of each year is not worse off than it was in the preceding year.”
ZRA said hydrological simulations which had been done show that it will take three or more years for Lake Kariba to recover to its normal levels.
Said University of Zimbabwe hydrologist Dr Hodson Makurira: “You can’t really tell whether Lake Kariba is likely to recover soon or not based on the good rainfall forecast. There are no easy answers. The linkages between a good rainfall forecast and water inflows into the lake are complex and probabilistic.
“Even if we have good rains, it’s highly unlikely that it will fill up. It takes several good rainfall seasons to get it to fill up.”
The UZ water expert said a better hydrological forecast for the lake could only be given based on inflows observed at various points along the Zambezi River.
“Based on observation, you are likely to make informed decisions rather than basing our forecast on the rainfall for one season,” said Dr Makurira.
“It’s like a bath tub – it depends on what gets in and what gets out through the drain plug. If the plug is too big and is letting out more water, then it will take time for the tub to be filled with water.
“So it depends much on the demand and supply of water. This is a prediction (rainfall forecast) and things can go wrong like it has happened in the past. We can only generate answers when we observe inflows from north-western Zambia where the river rises.”
To ensure, better recovery of the water levels in the lake, Dr Makurira said there is a need to strike a balance between demand and water storage as well as safety for the dam infrastructure.
“We can do simulations but observation is critical,” the UZ water expert said. “After a severe drought, very few dams can store and fill up with water. It takes two to three years with good rains.”
Dr Makurira said it was vital for ZRA to continuously monitor the usage of water by the two power utilities to allow for the lake to build up its water levels.
The ZRA says it is continuously monitoring, reviewing and informing the two utilities on the availability of water for power generation at Lake Kariba so that the power utilities can adjust their operations to allow for continued availability of water.
The water authority says power generation was at 12 percent compared to 65 percent when water levels were high.
The Zambezi River which rises in black marshy dambo and dense undulating miombo woodlands in the Ikelenge district in the North-Western Province of