Water Wheel May/June 2022: Dam Siltation

Abstract

MANAGEMENT Siltation of SA dams – Working towards a sustainable solution 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.

Categories