Analysis of surface changes in the Walbrzych hard coal mining grounds (SW Poland) between 1886 and 2009

Underground coal mining causes surface changes such as subsidence and land use transformations. The knowledge of the character of subsidence in both the past and present provides useful information, e.g. for spatial development. This paper presents a methodology of determining surface height changes based on cartographic modelling in geographic information system (GIS) for an old mining site. It has been applied in two test areas of a former coal basin in the Walbrzych region (SW Poland) characterized by complex geological and mining conditions. Surface changes have been determined based on available topographic maps of this area for a period of 123 years (1886-2009) as the result of a set of interpolation and map algebra operations. The elevation values reach 52 and 63 m for areas A and B, respectively, and the maximum subsidence values determined in GIS are 24 m for study area A and 36 m for area B. The former are associated with mining waste dumps. These results have been compared with the results of predictions based on the empirical Knothe theory of subsidence calculations using spatial statistics parameters. It has been found that Knothe theory-based modelling produces lower subsidence values and more uniform subsidence surface than the applied method based on the actual elevation data. This may be due to either the values of coefficients of subsidence used in the Knothe modelling method or the complex and complicated mining conditions (numerous overlying and inclined coal layers) of the Walbrzych Coal Basin. The calculated surface height changes for the analysed period are presented graphically and described.