Does snow actually matter for Cape Town’s dams?
· The South African
With fresh snowfall forecast for parts of the Western Cape this weekend, many Capetonians are asking the same question: Does snow on the mountains help fill the city’s dams?
The short answer is yes – but only a little.
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While snow eventually melts and contributes some runoff, it’s rainfall rather than snowfall that does the heavy lifting when it comes to replenishing Cape Town’s water supply.
Rain is the real source of Cape Town’s water
Cape Town’s drinking water comes from six major dams that make up the Western Cape Water Supply System, with Theewaterskloof Dam accounting for more than half of the network’s total storage capacity.
As of Thursday, 6 August, the combined dam system was sitting at 77.7% full – a healthy level for this stage of the winter rainfall season.
The water entering these dams comes overwhelmingly from sustained rainfall over the surrounding mountain catchments, rather than melting snow.
Although parts of the Western Cape experienced an early snowfall this winter, snow alone has little impact on overall dam levels.
Snow helps, but rainfall does the heavy lifting
Snow that settles on the high peaks around Villiersdorp, Franschhoek and other mountain catchments eventually melts and flows into rivers feeding the dams.
However, that contribution is relatively small compared with prolonged winter rain.
In contrast, widespread rainfall across the catchment areas can dramatically boost storage levels.
During one particularly wet spell in May, Cape Town’s dam system recorded an increase of around 20 percentage points in just a single week – far more than any snowfall event has contributed this year.
Good news for water security
While snow remains one of winter’s most spectacular sights in the Western Cape, hydrologists generally regard it as a bonus rather than a major source of water.
For residents hoping this weekend’s snow will significantly boost dam levels, the reality is that the accompanying rain is far more important.
The snowfall may add a small amount of runoff once it melts, but it’s the steady winter rainfall across the mountain catchments that ultimately keeps Cape Town’s taps flowing.
You can track the current combined dam level here, and see how this weekend’s system is expected to unfold.
Did you know snow played such a small part in Cape Town’s water supply?
Let us know in the comments below, Mzansi …
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