Recharge flooding of collieries in South Africa
Coal mining has been documented in South Africa as far back as 1838 and undoubtedly contributed significantly toward the economy as well as job creation (Barnes and Vermeulen 2012). Many mines in South Africa have changed the geology on a localized level by taking out the coal seams. The change in geology also changed the geohydrology. The voids that are left to fill with water. Most of that water will be groundwater, but some will be surface water and stormwater. In the geohydrology, we talk about the recharge of a mine. The recharge is depending on several factors, some depending on the physical mining methods and others depending on the geological setting. Recharge and mine flooding (opencast or underground) is nothing new; it occurs in every mine from the first day the mine was created. Recharge is a natural process; inundation is the act of intentionally flooding of land that would otherwise remain dry. Where inundation floods a mine using a single or multiple pumping locations, the recharge is a phenomenon that occurs over the full extent of the mine. Although recharge is often considered to occur equally over the full extent of the mine, this is not true. Many factors influence the recharge, such as rainfall and rainfall intensity, surface topography, depth of mining, geological structures, presence of subsidence, surface structures, and in case of an opencast mine, the state of rehabilitation. There are different ways to express recharge and is commonly defined as a volume [L³], typically m³. Recharge rates are expressed either as a flux [L³T-1 ] or as a flux density [LT-1 ] (Nimmo, J.R., 2005). Because recharge is depending on rainfall (without rainfall no recharge), the recharge is usually expressed as a percentage of the rainfall.