Understanding Groundwater Flooding in the Low Burren, Ireland

The Gort-Ardrahan region in the west of Ireland suffered flooding during the winters of 1989-90, early 1991, and 1994 and most severely in 1995, due to very severe prolonged rainfall events. The flooding created considerable hardship, some families having to abandon their homes permanently. The hydrology and geomorphology of the region is dominated by karst, and linked to an ecology sustained by seasonal lakes (turloughs), scattered across the limestone plateau. The area is characterised by disappearing streams, seasonal streamflow reversals and groundwater emergences as well as permanent and seasonal lakes. Spatially-extensive flooding occurred when the volumes of water contained within these turloughs overflowed their bounds. The system was investigated using a variety of techniques, including drilling, geological mapping, geophysics, and tracer studies. A thorough conceptual understanding of the karst aquifer and cave system was developed and represented using an equivalent pipe network model. Distributed rainfall-recharge inputs were provided using a GIS-based recharge model. Recharge from rivers entering the groundwater system was simulated using a hybrid conceptual-metric rainfall-runoff model. The karst network model was calibrated and validated over separate periods using stage measurements on several turloughs where the seasonal rise and fall of water level was observed over an 18 month period. Volumes were calculated using a detailed terrain model of each turlough. An extensive effort was required to characterize this complex system, However, the resulting model was sufficiently accurate to assess various proposed engineering options to alleviate potential flooding from future extreme events.