Congratulations, you’ve made it through 2018’s first month unscathed. No, that wasn’t me addressing you, but rather Cape Town’s ailing water delivery system.
Yes, yes, we know. You’re probably sick of hearing about #DayZero now, but it’s lurking in the Cape Town and South African cultural zeitgeist this year, and doesn’t show any signs of abating.
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So with that said, we put together four graphs summarising just how Cape Town’s dams fared during January, how much water we’ve consumed through this period, and the amount of rainfall some of the dams received.
All information in these graphs have been sourced from the City of Cape Town.
Dam levels
Cape Town’s total dam capacity fell by 4.7% between 1 January and 29 January — a drop of around 0.9% per week on average.
Ultimately, that’s not too bad, but looking at individual dams highlights the severity of the crisis.
The two largest dams — the Theewaterskloof and the Voëlvlei — were also the two with the lowest levels across the Western Cape Water Supply System (WCWSS).
The former also dropped 5.9% over the same period — a tangible decrease of nearly 28 000 ML (megalitres). That’s only slightly less than the total storage capacity of a completely full Steenbras Upper Dam.
Remarkably, only the Wemmershoek Dam remained level throughout the month, never dipping above or below its 52% comfort zone.
Dam capacity
Although the Berg River Dam is only the third largest in the WCWSS, it held more water within its walls than the Theewaterskloof and the Voëlvlei.
But at just 13.3% full, the importance of the Theewaterskloof within the system is clear: it still holds nearly as much water as the Steenbras Dams and the Wemmershoek combined.
Notably, the Berg River Dam also deserves a shout out, which was only added to the WCWSS in 2009. Without it, Cape Town would have some 70 000 ML less surface water stored than at present — effectively two Steenbras dams or around 17 weeks’ worth of water at 29 January’s consumption rate.
Note, the total storage of all six dams when full is just below 900 000 ML. Total storage as of 29 January 2018 is around 236 000 ML.
Water consumption
Speaking of consumption…
While dam levels have steadily declined since the beginning of the year, water consumption has been less stable and predictable.
Between 8 and 22 January, Cape Town used no less than 608-million litres of water per day. That’s more than 150-million litres more than the City of Cape Town’s target. Nevertheless, the city still deserves a pat on the back: its using less than half the water it consumed per day back in mid-2015.
But the week after showed a substantial decline –Cape Town used some 28-million litres less per day than the previous week.
Note, the City of Cape Town includes the six largest dams in the system — those listed in the first graph — as the “Large Dams”. An additional eight dams located across the Peninsula are included in the “All Dams” calculation.
Rainfall
Although SAWS suggested lower than usual rainfall for much of Cape Town through summer and into autumn, the Theewaterskloof catchment area actually received more rainfall than its long-term January monthly average — 30mm vs 21.2mm.
This however had no impact on actual dam levels, it seems.
Other areas didn’t fare well, according to the City’s data.
The Steenbras catchment area received just 2.9mm — well below its monthly average rainfall figures.
The Wemmershoek Dam also received just 6.8mm of rain in January, between two rainfall days.
And as for the Voëlvlei, it saw just one day of rain — 22 January — receiving just 3mm of rain.
Feature image: City of Cape Town
