VAAL FLOOD HISTORY

It comes as a shock every time the Vaal River floods and devastates towns, farms and tourist lodges. Yet the Vaal has a long and notable history of flooding that local communities ignore at their peril.

The highest flood ever recorded was in 1904, 119 years ago, when the river peaked at 7800cubic metres per second. Presumably this was below where Vaal Dam is now (the dam was first built in 1938 and later raised twice). I can’t find the exact location where that measurement was taken.

That amount of water is more than double what we have experienced, at worst, in the past fortnight when the highest level below Vaal Barrage was, I estimate, 3200cumecs. It’s an estimate because while the maximum released by the Barrage was about 2950 cumecs, other feeder streams – particularly the Kromelmboog from the NE Free State – spewed hundreds of cumecs more. Down at Schoemansdrift the recently improved road bridge was deep under water, overtopped by a volume probably exceeding 3200 cumecs as more feeders poured. And lower down still the Mooi river from Potchefstroom added to the level.

In the current flood, though, residents of the valley dodged a mega disaster. In 1904 the region was far less developed or settled than it is now. We were told on Saturday 18 February to expect 7300 cumecs. It never came, but had this quantity of water actually come down the valley whole communities would have faced a killer catastrophe. Numerous lodges and farms along the way would have been trashed and billions lost.

So common are floods on the Vaal that nobody should be surprised when they happen. Memories are short, however. As far as I can establish these are the flood years and rankings of river heights:

March 1904 – 7,860 cumecs

February 1954 – 6,980 cumecs

January 1996 – 6,800 cumecs

January 2011 – 6,200 cumecs

January 1988 – 6000 cumecs (?)

February 1970 – 5,740 cumecs

February 1975 – 3650 cumecs

February 2023 – 3200 cumecs

Figures can vary depending on where the measurement was taken and how measured.

One of the most tragic floods was in 1988 when 14 people reportedly died below in areas below Bloemhof dam. I cannot establish the flow rate but one report says it was between 6000-8000 cumecs. The lower down the river the flow is measured the higher the figure tends to be.

Note that January and February are the “flood months” although April can also see very high water due to Indian Ocean cyclones. Floods come regularly within a cycle ranging from about 7 to 12 years. The last big one was in 2010-11 in January when the peak at Parys exceeded 2800 cumecs.

An archival Pathe Newsreel from the 1940s shows a typical flood that could well have been filmed at the current time: https://m.youtube.com/watch?v=kxWlwroHPAU .

Given the figures for the past century, it’s doubtful that global warming is responsible for increased flooding. It may be that the intensity and frequency of rainfall is causing extreme events more often. Most likely, though, it is urbanisation that causes more runoff as larger areas are paved and roofed areas spread further.