eBusiness Weekly
Golden Sibanda
The amount of water flow on the Zambezi River has risen above the long term averages captured at two of the most important gauging stations along the river from North of Zambia through Lake Kariba, raising hope of improved electricity output at Kariba.
Water levels in Lake Kariba had fallen to critical levels last seen over 20 years ago, which prompted the Zambezi River Authority (ZRA), the administrative body in charge of the river and Lake Kariba, to cut water allocation for power generation by Zimbabwe and Zambia.
The two countries share the lake equally.
Zimbabwe has a 1050 megawatts (MW) power station on the southern bank of the lake, while Zambia also obtains the bulk of its power on the northern bank of the giant reservoir, the world’s largest manmade inland Lake. Starting in the north of Zambia, the river makes its long journey through Zambia, Zimbabwe, Angola, Namibia and finally Mozambique before emptying into the Indian Ocean.
The latest data provided by the ZRA as at March 27, shows that the water flow at Chavuma, upstream of Victoria Falls, has risen above quantities recorded at the same time last year and the river’s long term averages recorded at two of 14 important gauging stations on the Zambezi River.
“The Zambezi River flows rose from 236 m3/s at the start of January 2020 to a peak of at 5006 m3/s recorded on 25th February 2020 after which the flows receded. However, the Zambezi River at Chavuma Station is known for its double peaks in flows and has accordingly again begun to increase. As of 27th March 2020, the river flow was at 4559 m3/s while last year same date it was 732 m3/s.
The obtaining river flow at Chavuma has continued to trend above the long-term average of 2005 m3/s by 127 percent,” ZRA said in a statement released recently.
The recorded flow at Chavuma is higher than that recorded on the same date in 2019 by 523 percent and ranks highest in the last 20 years. However, there is a four (4) weeks’ time lag for the flows at Chavuma to reach Victoria Falls owing to the significant influence of the Barotse Flood Plains situated between the two stations.
The Barotse Flood Plains, which form the most important catchment area of the Zambezi River, are now full and the flood waters have now began to arrive and increase the flow at Victoria Falls, peaking around April.
The Zambezi River flows monitored at Victoria Falls rose from 349 m3/s at the start of January 2020 to 3890 m3/s recorded on 27th March 2020. Last year on the same date the recorded flow was 800 m3/s. The flows are now 54 percent above the recorded long-term average flow of 2522 m3/s for this station.
The lake level at Kariba rose by 97cm between January 1 2020 and 27th March 2020. This recorded increase in the lake levels at Kariba is attributable to the improvement in the inflow from the upper Kariba Catchment.
As of 27th March 2020, the recorded lake level at Lake Kariba was 477,64 meters, signifying 14,86 percent live storage or 9,63 billion cubic meters (BCM) of usable storage with the lake being just over 2 meters above the minimum operating level (MOL).
However, this recorded volume of stored usable water is still 60 percent lower than that recorded on the same date last year at a lake level of 480,73m with 24,16 billion cubic meters or 37,28 percent usable storage when the lake was 5 meters above the MOL.
When filled to capacity the Kariba Dam water level rises to about 485 meters beyond which overflow gates have to be opened.
During the period October 2019 to Mid-March 2020, the total inflow into the Lake stood at 10.54 BCM when the historical average for this period is no less than 14,39 BCM. The below average inflow recorded to date under the 2019/2020 rainfall season accounts for the low water levels still characterising Kariba.
ZRA allocated 22 BCM to be shared equally between the two power stations at Kariba, effectively limiting the combined power generation output to an average 550MW (or 275MW for each of the two power plants at Kariba).
The authority said it has maintained this water allocation for the remainder of the 2020 period in the wake of the below average lake inflows under the 2019/2020 rainfall season in an effort to ensure building up the reservoir storage.
The low water levels at Karibba affected power supply in Zimbabwe, which requires about 1 800MW at peak periods of demand, but can only generate around 500MW, also weighed down by low output at Hwange, the country’s second largest and only other major power plant.
Zimbabwe is supplementing its internal generation supply with imports, but this is not sustainable and consistent given the prevailing shortage of foreign currency required for other critical needs.
Hwange Thermal Power Station has rated capacity of 920MW but can only average 450MW at best due to lack of spare parts and frequent breakdowns as a result of the plant’s advanced age.
Lake Kariba has capacity of 186,6 billion cubic meters when full (486 meters).
The total inflow into Lake Kariba in 2019, when the dam was affected by the drought that hit areas around its catchment areas, the total inflow into Kariba was 18,84 billion cubic metres, 70 percent below 2018.
On the other hand, the total outflow last year was 45,81 billion cubic metres comprising 36 billion cubic metres turbine outflow discharge and 9,79 billion cubic metres water lost through evaporation, which reduced reservoir storage by 26,97 cubic metres.
