Page 16 -

PRECINCT LIVING

OUR FICKLE

WATER SUPPLIES

BY JAMES CLARKE, PICTURES BY MARY BROADLEY

hose magnificent rains we had in urban areas with all their non-absorbent - not a great deal deeper than the deep
Gauteng early last month could concrete and tarred surfaces, runoff end of a swimming pool. Having such a
not have come at a better time. throughout the rainy season can be as wide area and shallow depth, a third of its
TWe’d already had fair summer high as 80 percent. But high-density water evaporates annually.
rains which gave rural people who have urban areas take up very little of the
no tractors and rely on draught oxen, a country’s 1,2 million square kilometres. While small dams in housing estates
chance to plough and sow fairly early. are valuable shock absorbers during
Some years, they have to wait as late The volumes we witnessed last month floods, they too are becoming
as January, which misses a lot of the were vital to the Vaal Dam (Gauteng’s shallower and shallower. One estate
growing season. main supply), as well as to the Vaal’s in Greater Johannesburg spent around
lower dams and to Hartbeespoort whose R1-million to dredge its two heavily
The value of February’s rains had water feeds a critically important crop- silted lakes. Months later, silt from
another dimension. Our summer rain was growing area. local developments, including highway
obviously vital to agriculture. It was also widening, totally filled one lake and
economically important to those of us However, there was a hidden cost. halved the size of the other.
who are heavily invested in our gardens,
and to our estates that spend millions on Many of us witnessed the volumes The total runoff from every river in South
landscape gardening. sluicing down our stormwater drains. Africa (53 billion cubic metres) would fill
By the time that water hit the open only a third of Kariba Dam. The country’s
But February’s marvellous storms were of countryside, its velocity and volume biggest dam, the Gariep on the Orange
much wider importance. Only towards the tore away at the rivers banks and the River, could, years ago, store 6 billion
end of summer does the ground become topsoil. As the muddy water entered the cubic metres. It is now greatly reduced
saturated and so we get what we so Vaal Dam, its flow rapidly slowed down, by silting and, of that volume, 2 billion
badly need - runoff. allowing the silt to settle and reduce the cubic metres are lost annually due to
dam’s depth and storage capacity. evaporation.
Generally in Gauteng, of every 100 drops
of rain that fall, only three or four find On average, the Vaal Dam’s 340 sq km One wonders that more damage was
their way to the dams. Although, in surface is, nowadays, only 3 metres deep not done during February’s storms.

1614 15
DPL
DPL
DPLDPL