An evaluation of urban flood estimation methodologies in Ireland

This paper summarises the findings of a study to evaluate the use in Ireland of the different flood estimation methodologies that can be applied to urban or urbanising catchments. The study, undertaken as part of the Office of Public Works‟ (OPW) Flood Studies Update programme, comprised both quantitative (posted questionnaires) and qualitative research (focus groups) targeting a range of organisations involved with planning and design issues pertaining to urban flooding. A total of 291 questionnaires was circulated. Of these, 100 were returned, equating to a response rate of 34%. Results indicate that formulae and methods for determining runoff rates in urban and urbanising catchments are being applied very generally without due consideration being given to the statistical foundation underlying the methods. The resulting inconsistencies in estimated runoff rates highlight the need for National Guidance for flow estimation in urban and urbanising catchments in Ireland.