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Under the new European Union Bathing Water Directive (2006/7/EC) which comes into force in 2014, more stringent bathing water quality standards, defined in terms of Escherichia coli (E.coli) and Intestinal Enterococci (I.E.), will apply in Irish bathing waters. Compliance with these standards is ensured through a structured water quality monitoring programme that is published by Authorities with responsibility for bathing water areas in advance of each bathing season. The directive recognises that elevated levels of faecal coliform bacteria in bathing areas can derive from the overland transport of waste from livestock in the rural fraction of river catchments. On days therefore, that follow significant storm events in coastal agricultural catchments, exceedences of threshold bacteria levels may occur. Given that these exceedences result from ‘natural’ rather than anthropogenic influences, a ‘discounting’ mechanism that allows for a temporary relaxation of these standards is allowed for short-term pollution incidents. In this regard, some high levels of faecal bacteria contamination can be excluded from the water quality record. However, this ‘discounting’ is only permitted if elevated bacterial levels are predicted in advance and mitigation actions to maintain public health protection are taken. This paper presents an integrated catchment (MIKE11) and 3-dimensional coastal (MIKE3) modelling tool for predicting the bathing water quality at Bray, Co. Wicklow. Models were calibrated using flow and water quality data. Adjustment of the M2 and S2 tidal constituents of the MIKE global model has resulted in an improved fit to measured water levels at the five reference tidal gauges. Bottom friction was calibrated to produce good correlations of measured and simulated current speed and direction. Furthermore, results of the water quality transport model has shown that the model has adequately replicated measurements of E.coli and IE.
O'Sullivan, J.J. et al. (2013) Bathing water quality prediction using an integrated catchment and 3-D coastal hydrodynamic model. International Symposium on Water Resources and Pollution Control in Arid/ Semi-arid Regions (ISWPAR) Xi'an, China, 21-23rd June 2013, pp 493-500.