Mining activities in South Africa over the past 120 years have changed the natural environment in several ways. A legacy of many mining areas in South Africa is not only the abandoned mine infrastructure at the surface, but also near surface mined out areas. Current challenges for mining companies lie in rehabilitating the natural environment and preventing further environmental degradation. One particular area of concern is surface deformation associated with mining activities, particularly mining subsidence. Mining subsidence associated with underground coal mining is, in theory, a gentle, gradual settling of the earth’s surface (Perski & Jura 2003). Underground mining cavities can result in a lowering of the earth’s surface (hereafter referred to as surface subsidence) as a result of the collapse of bedrock and the subsequent sinking of unconsolidated surface sediments (Perski & Jura 2003). Some of the primary effects of the collapse of underground cavities include the appearance of tension cracks and crownhole development. The effects of surface subsidence on the built environment are severe and include damage to infrastructure (roads, dams, pipelines and buildings). The effects of surface subsidence on the natural environment include the alteration of hydrological pathways. The ponding of water in subsidence basins results in an increase in groundwater recharge. The groundwater circulating through mining cavities becomes polluted and discharges into the natural environment contaminating wetlands, streams and dams. Two areas of particular concern were surface subsidence is concerned is the undermined areas of the Witwatersrand goldfields as well as underground coalmining in the Witbank Coalfields (figure 1, 2, 3 & 4).

The report describes the surface deformation features associated with mining activities in two case-study areas associated with gold mining activities in the Witwatersrand gold fields and coal mining activities in the Witbank coalfields respectively.

Figure 1 – The effects of deformations