17 August 2023
By: Alani Janeke
Weather models indicate that an El Niño system will strongly influence summer weather patterns. While South Africa’s dam levels are currently favourable, one should always plan for drier seasons ahead.
Most South African dams are looking healthy, but water levels must be managed optimally because an El Niño system in summer could lead to below-average rainfall, says independent agricultural meteorologist Johan van den Berg.
The main Western Cape dams are 91.1% full, on average, compared with 63.6% a year ago. Theewaterskloof, the largest dam, is 101% full compared to 76.6% a year ago.
“From an agricultural perspective, the Clanwilliam Dam is of great importance as many large plantations, especially citrus and grapes, rely on it,” says Van den Berg.
“This dam needs to be almost full by the end of the rainy season to provide sufficient water for the summer season, as it has been overused. Currently, it is at 97.8% compared to last year’s 55.9%, which is extremely favourable.”
Van den Berg says conditions have also improved in the Eastern Cape, where average dam levels are 81.5% compared to last year’s 69.8%.
Kouga Dam, which last overflowed in 2015 and hit a low point of about 5% in the past few years, is at 54.6% compared to 16.7% a year ago.
But Impofu Dam, an important water source for the Nelson Mandela Bay metro and surrounding areas such as Humansdorp, is only 15.9% full compared to last year’s 10.1%.
The other dam that supplies water to this area, the Churchill or Kromme Dam, has risen to 72.7% compared to last year’s 19.1%.
In the Free State, where most large dams are shared with other provinces, the average dam level is 97.3% compared to last year’s 99.8%.
“Of the larger dams, the Vaal Dam currently has the lowest level at 89.5% compared to last year’s 110.6%,” says Van den Berg.
“It is encouraging that almost all smaller dams are also at very high levels. The two large dams in Lesotho are also at favourable levels and more than 90% full.”
El Niño and planning
Van den Berg says although an El Niño system is on the horizon for the summer, high dam levels will help to ensure a good irrigation production season if load-shedding isn’t too severe.
“The expectation is that much less water runoff will occur in at least the 2023-24 summer season, and thus dam levels will quickly start to decline, especially in the summer rainfall areas,” he says.
“With the current good water status, there should be enough water for the upcoming season, but it could become a problem if weaker rainfall conditions occur in the coming seasons.”
He suggests the following key principles and management measures while dam levels are favourable:
- Irrigation scheduling is extremely important to ensure optimal water use and yields.
- Illegal water use must be halted. Overuse is at a serious level, although its extent is not known. In the past three seasons, above-average rainfall meant there was no water shortage, but with less rain expected in the next seasons, the extent of overuse will become evident.
- It’s important to consider the stability of the water source, especially when planting permanent crops such as nuts, fruits and other tree crops. To prevent significant production damage to permanent crops and irrigation systems, more annual crops should be planted. This should then be seen as opportunistic production when water is available.
- Water quality will become a bigger problem in drier years when the dilution effect of abundant rain is not present. Problematic situations should be identified, and corrective measures taken. With phytosanitary regulations becoming stricter, especially in Europe, poor water quality could pose a significant risk for the export of products and market access.