When we non-specialists think of silted-up dams (indeed, when
we think of them at all) we picture in our mind’s eye great
expanses of desiccated mud, cracked and fissured beneath a
baking sun. But scratch the surface, or rather dig down a metre,
and a more promising picture beckons: water. Certainly, that’s
what a recent pre-feasibility study found at the Eastern Cape’s
Nqweba Dam.
When Nqweba (Xhosa for “meeting place”) was first completed
in 1925, known then as the Van Ryneveld’s Pass Dam, it had a full
supply capacity of nearly 79 million cubic metres. Fast-forward
to 2011 and its capacity had shrunk by 43%. Built for irrigation,
today, it cannot meet the domestic and industrial needs of the
nearby Karoo town of Graaff-Reinet.

The problem is not so much an absence of water as a surfeit of
silt. Fine sand and clay – from natural erosion, exacerbated by
overgrazing – carried by the Sundays River and its tributaries are
choking Nqweba. A similar story can be told of many of the 320
state-owned dams managed by the Department of Water and
Sanitation. Although siltation rates vary dramatically, on average
South Africa’s dams are losing capacity at a rate of 0.4% a year
with consequences for water and food security, particularly
during drought.
What’s to be done?
The department has long supported surveys and studies to
better understand a problem that is far from unique to South
Africa: Worldwide dams are losing 0.8% of their capacity a year.
And it underwrites the National Dam Silt Management (NatSilt)