Automation in Mine Water Balance Calculations
Institute for Groundwater Studies, University of the Free State, South Africa
Every mine will experience some sort of water make during its life and beyond. The described software was developed for the collieries in the Mpumalanga coal fields of South Africa. The water balance for a mine during its life of mine depends on the amount of water it receives, stores and discards. The quantity of water it will receive depends on the type of mining, the geology, presence of groundwater, amount of precipitation, size of the operations and the type of rehabilitation. The water make calculations are complicated by the fact that the outline, the type of mining and the state of rehabilitation will change during the life of mine. An opencast mine’s spoils (overburden) will be placed back in the pit, levelled, covered with a topsoil and grassed. All these phases of rehabilitation have different recharge factors while the aerial extend of the stages will change during the mining and rehabilitation process. Underground operations experience water-make from recharge through the overlaying strata or by lateral (groundwater) flow. The depth of mining will vary from area to area and the mining type can change from bord- and pillar in one section to long-wall mining in another. It is also possible that bord- and pillar mining is performed initially followed by some form of high-extraction or full extraction on the way back. The different mining methodes may result in different recharge factors. Water recharging an underground mine will first accumulate in the local floor depressions and once they are filled water will flow to the lower parts of the mine. When the water make is too much, excess water may be stored in abandoned underground sections, behind the contours or water retaining walls (seals). Monitoring boreholes and vertical fractures makes it possible for the water pressure to rise to very high values. Seal failure will result in large volumes of water flowing through the mine. For personnel safety it is vital to know where the water will end up. The method developed is an analytical model that is part of the Windows Interpretation System for Hydrogeologists (WISH) and takes all these factors into account. For each part/section of the model parameters like time dependend recharge factors, extraction factors and water level elevations measured can be assigned. Stage-volume curves as well as time dependend volume- and capacity can be calculated.