Degradation of dam reservoirs under the influence of mining subsidence in Upper Silesian Coal Basin, South Poland

Abstract

Exploitation of mineral resources can result in dramatic multidirectional changes in the natural environment in mining areas, with the changes being particularly evident in the form of land degradation. One of the consequences of underground mining is subsidence of the overlying surface of the land area. The greatest subsidence typically occurs when the mining operation is carried out with a longwall top coal caving process, which can result in subsidence basin deformation developing on the surface. This development can lead to a change in natural landforms. As a consequence of the development of subsidence basins in the present study, the maximum depth in the Upper Silesian Coal Basin may exceed 30-m, which can also change the hydrological conditions of the area. Development of subsidence basins can often lead to changes in the morphometric parameters of the existing hydrographic objects, a phenomenon that also applies to dam reservoirs. As a result of land subsidence, the depth and surface area of hydrographic objects can increase, with the maximum depth point moving deeper into the reservoir outside the frontal barrage zone, with changes also occurring in the reservoir tank morphometry. In extreme cases, the barrage may stop water damming, being located outside the reservoir zone, meaning the tank's water management function is lost. All the reservoirs in the current study are located in the Upper Silesian Coal Basin in southern Poland, which is currently the only significant coal-mining centre in Europe, with the surface area of the basin being 7490 km².