Southern Africa: Relief As Zambezi River Shows Increased Flow

The second half of the rainy season 2019/20 has brought relief to most parts of southern Africa, with increased water flows recorded in the major gauging stations along the Zambezi River.

A gauging station is a facility used to take measurements of data on terrestrial bodies of water for planning purposes.

According to the Zambezi River Authority (ZRA), the Victoria Falls - one of the key stations on the Zambezi River - recorded flows of 4,289 cubic metres per second on 31 March. Last year on the same date the recorded flow was 816 cubic metres per second.

The flows this year are 54 percent above the recorded long-term average flow of 2,522 cubic metres per second for this station.

The increased water flow at Victoria Falls is the highest since 1958 when the flow reached 10,000 cubic metres per second during the construction of the Kariba Dam.

This increase is therefore contrary to some media reports which had indicated that the Victoria Falls, located between Zambia and Zimbabwe, was in danger of drying up as the river levels dropped.

Downstream of Victoria Falls, the level of Kariba Lake has continued rising steadily, recording 478.2 metres on 6 April, although slightly lower than last year's level on the same date.

This is about three metres above the minimum operating level for power generation at Kariba power station.

The Victoria Falls is one of the world's natural wonders, and an improvement in water flow is a big boost for the tourism sector, including domestic tourism, as it brings an extra attraction for visitors to the falls to watch the thundering wall of falling water at full length.

The constant spray from the waterfall supports a dense woodland vegetation known as the Victoria Falls Rainforest. This flora, in turn, supports a varied diversity of insects, amphibians, birds and mammals.

According to a forecast by ZRA, the water flows at Victoria Falls are likely to increase in a second peak period expected in April.

The increased flows are a result of intense run-off from the high rainfall received at the source of the Zambezi River in the Chavuma area of northwestern Zambia close to the border with Angola.

The Chavuma Gauging Station recorded an increase of more than 500 percent from the 2019 flows.

The flow on 6 April for example, was recorded at 5,825 cubic metres per second while the flow observed on the same date last year was only 695 cubic metres per second.

The ZRA predicts that Chavuma is still to reach its peak, similar to the forecast for the Victoria Falls.

The Southern African Regional Climate Outlook Forum had predicted normal to above-normal rains between January and March 2020 in most of Angola, and northern and western parts of Zambia, with areas further south receiving normal to below-normal rainfall.

Before reaching the Victoria Falls, the Zambezi River flows through the expansive Barotse floodplain in western Zambia, which soak up water during the rainy season and only when they get saturated do they release the bulk of the water, about 80 percent, which then finds its way into tributaries and rivers that eventually empty into Zambezi River.

The floodplain, which is estimated to store 8.6 billion cubic metres of water, draws much of the flows that were recorded at Chavuma.

Once the Barotse floodplain is full, the water flow starts increasing towards the Victoria Falls.

The peak at the falls is expected around mid-April, with roughly 625 million litres of water flowing over the edge per minute. This huge volume of water produces a spray that rises more than 500 metres into the air.

While climate change is taking its toll there is need to take note of the seasonal variations in flows.

There is a time each year when the Victoria Falls is seasonally low, around December of every year, particularly so after a drought as was the case last year.

The seasonal variations of high and low flows have long been observed by the Lozi kingdom in the Barotse floodplain of western Zambia. To cope with the floods, the Lozi have developed a lifestyle based on the seasonal changes of the floodplain.

Around the end of March or early April each year, the paramount chief, the Litunga, leads the Lozi people and their cattle to higher ground at the flood-time capital of Limulunga, in a traditional floodwater ceremony known as Kuomboka.

According to the ZRA, the water coming into the Barotse floodplain hit just over 5,000 cubic metres a second at the end of March. This has been the highest flow recorded in 20 years.

Consistent heavy rains in the second half of the 2019/20 rainy season have caused flooding and affected people over parts of Angola, DRC, Mozambique, Tanzania and Zambia.

In Mozambique, almost 60,000 people were affected by heavy rains and flooding in January, primarily in Zambezia, Cabo Delgado and Sofala provinces.

In February, heavy rainfall increased the levels of the Buzi and Pungwe rivers, causing further flooding and damage in the central provinces of Sofala and Manica.

For other parts of the region, a late start to the rainfall season and uneven rainfall distribution contributed to persistent moisture deficits and dryness.

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