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THE storm on 9/11 was so extreme and so widely reported that a Kenyan friend, currently on a fellowship in Washington DC, emailed me: “Are you safe, Mandi?”
“As it happens, all the flooding took place on the other side of Joburg,” I replied. “So I’m fine – what about you? Are you safe?”
According to an Engineering News story (November 10 2016), “Sanral bridge network manager Edwin Kruger said the freeways would have, in the past, been designed to pass a one-in-twenty-year flood or up to a one-in-fifty-year flood, in the case of larger rivers.
“This means that, in any year, there is a 5% chance that a flood of this magnitude or greater will occur if the design recurrence period is 20 years. ‘The design standards used in South Africa are very similar to the varying international norms,’ he noted.” Added that the flooding experienced last Wednesday was a “one in a hundred year” flood, which usually means there’s a 1% chance of such a flood each year.
But things are changing, as gazillions of experts, from the UN to research institutues to insurance companies have noted. “Escalating temperatures will bring about stronger floods as well as a rise in the prevalence of floods, droughts and heat-waves,” writes E Matuszewska in Potential Climate Change Impacts for Johannesburg.
It’s a two-fisted punch: overall, the country will suffer a reduction in precipitation (rain), but when it comes, it’ll likely sock us with downpours of 150 ml in half an hour (which is what happened on Wednesday last week, or so reports had it). Watching all that glorious water swirl away, taking cars and street signs and trolleys and suburban walls with it, felt like watching a tragedy. We have been so parched in Joburg!
In part, this is due to a phenomenon first recorded by Joni Mitchell:
They paved paradise, put up a parking lot
With a pink hotel, boutique and a swinging house-bar…
“In Johannesburg, owing to the intensification of migration and urbanisation, there is a lack of green spaces, but a prevalence of informal settlements, thus exacerbating the risk of damage, because man-made surfaces influence the speed and directionality of floods,” writes Matuszewska.
Pave the earth over, seal it in, and what can the water do but gather speed and power as it races downhill, until it churns into a dip like the Augrabies in flood? Culverts and stormwater drains channel the rainwater and create whitewater tributaries that add to the flash flood.
Water scours out everything in its path, of course; so it tears away a house alongside the river bank, along with the long-drop the resident has installed and all the faecal matter beneath it; it roars through industria and around waste, picking up chemicals and particulate matter – pollution was one of the risks facing clean-up officials and residents after Louisiana’s recent 1 000-year flood.
And where it crosses open land, dried out by prolonged absence of rain, it rips off topsoil and takes it away to silt up dams or damage river banks.
We need to rethink how we handle flooding in urban areas like Joburg.
We should employ water-sensitive urban design, not as a nice-to-have for the yoga-and-tofu crowd, but as an essential. Swales, for example, are natural or engineered dips in the landscape that often have a parabolic shape, filled with vegetation. They slow and stop water, letting it sink in to the soil. Attenuation or retention ponds have a similar effect.
Rivers and streams should ideally not be channelled in concrete (as they all too often are in urban areas); they should be allowed and facilitated to spread out over ‘flood plains’, which also slows water movement and allows it to sink in, recharging water tables.
Paving should not be allowed unless it’s absolutely necessary. Gravel permits water to pass through to the soil and holds it long enough to let some, at least, sink in. (Water sinking into earth also limits the disease potential of standing water in a warm climate, a standing invitation to bacteria and disease vectors like mossies.)
Every new housing development should come with rainwater harvesting as standard – not just to capture water that can reduce demand on dam and reservoir water, but also to prevent water racing off roof after roof, onto paved parking lots, down stormwater drains and into the race.
La Niña is expected to arrive in late December, they say; these storms may be the advance notice of her arrival. At last, we should have rain; but it may takes years for systems like the several dams that make up the Vaal system to fully recover, and we may find ourselves in drought years again sooner than anticipated (recent science indicates that climate changes are gathering pace amazingly fast).
So instead of simply rejoicing in the rain, we should as businesses and active citizens be doing what we can to learn how to prevent floods and harness every precious drop – and lobbying local government to show vision in managing a country that is getting drier over the years. “Dry – but you can still drink” should be our motto, neh?
*Mandi Smallhorne is a versatile journalist and editor. Views expressed are her own. Follow her on Twitter.
