Verspreiding van sinkgate en versakkings in die dolomietgebiede Suid van Pretoria

Abstract

The area south of Pretoria is presently experiencing a rapid growth in township development. This area is situated between Pretoria and Johannesburg and its popularity can be ascribed to the good infrastructure which makes Pretoria and Johannesburg easily accessible. Large portions of this area are underlain by dolomite of the Chuniespoort Group. This geological formation is susceptible to sinkhole and doline formation (collectively referred to as events), which can cause severe damage to structures and lead to loss of life. In this study the occurences of sinkholes as well as dolines are analysed and special attention was given to: - the collection of all information on known sinkholes as well as dolines, - the occurrence of sinkholes as well as dolines on the different gravity anomalies, - the presence of sinkholes as well as dolines on the different geological formations, namely the Eccles, Lyttelton, Monte Christo and Oaktree Formations, - the relation between rainfall and the formation of sinkholes as well as dolines, - the influence of urban development on the formation of sinkholes as well as dolines. A distinction is made between events caused under natural conditions and those induced by human action. Much of this information is classified. Therefore a locality plan indicating the exact position of the events is not included. This information is available for selected persons at Geological Survey. The following conclusions are drawn: 1) There is an equal occurrence of sinkholes and dolines on the different gravity anomalies. 2) A linear relation was found between the number of sinkholes and cumulative rainfall per month. 3) It was not possible to determine if events occur preferentially on the chert rich formations. 4) More events occur in the old light industrial areas. This can possibly be explained by the better water management in the old residential areas.