Monitoring the morphodynamic behaviour of a breached barrier beach system and its impacts on an estuarine system

Coastal erosion is often attributed to significant meteorological driven events, climate change, human interference etc. However some erosion events form part of a cycle of behaviour for a particular coastal system that is not specifically associated with any of the above. From an assessment point of view it is important to be able to identify such cycles of behaviour and then determine the best course of action. The barrier beach at Rossbeigh, County Kerry, Ireland, started to erode rapidly in the early 2000´s. By 2008 approximately 1.5million m³ of sand had been eroded and during the winter period of that year the dune was finally breached resulting in a small barrier island and a new tidal inlet. The initial breach length was 500m and it has continued to expand. As there was no immediate or potential infrastructure losses associated with this erosion, a policy of no interference was adopted by the coastal authority. This thus provided the opportunity to study the evolution of a natural dynamic system at a time of significant change. However since then there has been anecdotal evidence of increased flooding in the estuary and changes to tidal channels reported. A research project has been ongoing at the Hydraulics and Maritime Research Centre of University College Cork since the breaching event. It aims at understanding the specific morphodynamic evolution and hydrodynamic behaviour of this coastal system and its impacts on the estuarine system protected by it. Preliminary indications suggest that the erosion rate is reducing and that a self healing process is commencing on the breach area. In addition a long term cycle of behaviour has been identified. Initial numerical modelling results indicate a change in current patterns as a result of the breaching. It is envisaged that combining long-term analysis with specific short term monitoring campaigns will add significantly to understanding of the morphological response to this dune breach and its effect- - s on the estuarine Castlemaine Harbour. The analysis at several spatial scales will provide an insight into the effect the breaching has on the entire coastal/estuarine system. This data will also be used to calibrate the numerical model, which will predict the evolution of Rossbeigh barrier beach after breaching under various meteorological and hydrodynamic conditions and its effects further landward in the estuary.