The influence of fractures on topography and groundwater flow in the Burren and Gort lowlands, western Ireland

Abstract

The primary hypothesis of this thesis is that "Topographic depressions are located along areas of high fracture density" and by association that topographic depressions will identify areas of high fracture density, A secondary, associated, hypothesis is that the "Fracture density controls the flow of fluid in the study area and the morphology of the cave systems". This thesis was examined through the analysis of three separate but inter-linked data sets; the fracture network, the cave systems and the geomorphology of the region, which were collected and analysed using a GIS. The study area chosen was the Burren and Gort Lowlands regions of north Co. Clare and south Co. Galway, due in part to the dramatic variation in topography between these Lower Carboniferous limestone dominated regions. In regions where the matrix is impermeable, such as in this instance, fluid flow is confined to the fracture backbone of the region. In order to understand groundwater flow a detailed understanding of the fracture pattern of the region is essential. Understanding the flow of groundwater in the area is important from an environmental, economic and natural resources point of view. In order to investigate any influence fracturcs have on topography it is necessary to map the fracture pattern of the region in detail. When the fracture maps were complete the fracture system was analysed and percolation theory was used to establish the backbone of the system. The terminations of the system were classified into three categories, blind, abutments and cross; from this the connectivity of the system was calculated. The topography of the region was examined through surveyed profiles perpendicular to features and interrogation of a Digital Terrain Model. The length, morphology and orientation of series of cave passages from a number of different caves were analysed. Flow directions of groundwater in the region were obtained. Once the data had been collected it was input into a GIS where the spatial distribution and interactions between the data sets could be examined.