Low productivity and typical heterogeneous conditions within poorly productive aquifers have resulted in very few detailed hydrogeological assessments of these bedrock aquifers being carried out in Ireland to date. This study carries out detailed characterisation of aquifer properties and geological structures on three catchment sites in order to refine the current generic conceptual model of poorly productive bedrock, adopted by the Irish Environmental Protection Agency. Hydrogeological properties were determined using hydraulic head data, pumping tests and tracer tests from borehole studies. Structural bedrock properties were investigated using borehole geologging, outcrop fracture analysis, and areal lineament mapping. Hydrological catchment characteristics were investigated by means of simple water balance approaches. Data results were synthesised into one coherent conceptual model of groundwater flow in poorly productive bedrock aquifers, for each of the three study catchments and for one generic-type Irish model. Very low flows encountered in many of the study boreholes proved challenging for conventional borehole flow methods. A new simple, effective pumpback dilution test for single boreholes was developed during this research, which successfully identified hydraulically active fractures which intersect the borehole at depth. This relatively cheap test can be completed in a small number of hours, and is also applicable to other aquifer types. The study concludes that detailed structural and/or tectonic models alone may not always be representative of the open discrete fracture systems which facilitate flow in the aquifer. Instead, emphasis should be placed on identifying representative numbers of hydraulically active fractures at depth in an aquifer, for which distinct fracture sets can be identified and used to generate open fracture network models. Only then may reliable estimates of aquifer permeability and contributions to surface waters be made, for site-specific catchments.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:677958 |
| Date | January 2015 |
| Creators | Nitsche, Janka |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0016 seconds