Title: Characterisation of diffuse recharge into karst aquifers using chemical and numerical modelling technique
Researchers: Philip Shuler, Prof. Laurence Gill
The aim of the research is to investigate three separate karst aquifers in Ireland with particu-lar emphasis on the characterisation of the diffuse recharge aspect in order to develop more realistic numerical models of the systems. These models can then be used to make predic-tions as to the aquifer response due to climate change, develop engineering solutions to po-tential flooding predictions, evaluate contaminant transport and land-use options as well as other applications such as the potential for hydropower recovery, for example.
The numerical modelling approach is based on the principles applied in the lowland karst area of south Galway in the west of Ireland which accurately simulates the temporal flooding dy-namics of the turloughs on the network (Gill, et al., 2013). This modelling approach, which models the turlough as reservoirs sitting on top of a pipe network, has worked well with re-spect to the water levels but it is recognised that it is limited as to the accuracy of the repre-sentation of the diffuse autogenic recharge into the network. Such autogenic recharge is of significant interest particularly from a contaminant transport perspective (for example, it may yield the correct volume of recharge into the conduits but drastically under / overestimate the time of transport). Hence, this project will investigate three different karst networks each with different characteristic found in the Irish context, all with autogenic recharge: a lowland karst aquifer (Ballindine, Co. Mayo); a lowland midland karst aquifer (Manorhamilton, Co. Leitrim); and a complex coastal upland karst aquifer (Bell Harbour, Co. Clare).
The research will employ a number of different investigative techniques to attempt to charac-terise the more diffuse flow input and transport through the karst system in these three differ-ent aquifers. Then, once characterised, the research will move onto trying to represent this flow in numerical models.
The investigative techniques will involve both chemical (isotopic and trace element water quality) and spring hydrograph source separation techniques. Water quality sampling will be required in order to analyse for isotopic fractionation techniques using stable isotopes (oxy-gen-18 and deuterium) as well as using anions, such as silica. In addition, numerical analysis of the spring hydrographs of Ballindine and Manorhamilton will be used to differentiate the fast response to the slower more diffuse response, for compari-son with the water quality results. Different numerical techniques will be trialled such as those developed by Kovács et al. (2005) in the Jura mountains to characterize flow systems in karst aquifers by acquiring quantitative information about the geometric and hydraulic aquifer parameters from spring hydrograph analysis.
The project objectives are to: 1. Reliably delineate the catchment boundaries of Bell Harbour, quantify its dis-charge over at least one year as basis for a profound hydrogeological under-standing as basis for any recharge-discharge assessments; 2. Differentiate between diffuse and conduit flow pathways into a karst network using both chemical (isotopic and trace element water quality) and spring hy-drograph source separation techniques; 3. Develop numerical (pipe network) models of the three karst aquifers that allow to distinguish different flow components as a result of the intrinsic heterogenei-ty of the aquifer.