The Planning System and Flood Risk Management - Offaly County ...

• Flood zone C – where the probability of flooding is low (less than 0.1%or 1 in 1000 for both river and coastal flooding).132.24 These flood zones are determined on the basis of the probability of river andcoastal flooding. Floodplains will primarily be found in flood zones A andB, and these zones will identify the spatial extent of a floodplain (see also para.2.36 below).2.25 The flood zones should be determined, ignoring the presence of flood protectionstructures. This is because areas protected by flood defences still carry aresidual risk of flooding from overtopping or breach of defences and there isno guarantee that the defences will be maintained in perpetuity. This residualrisk needs to be factored in to decision-making processes in both a developmentplanning and development management context, as well as in emergencyplanning.2.26 These flood zones are indicative only of river and coastal flooding. Theyshould not be used to suggest that any areas are free from flood risk, sincethey take account of only river and coastal flooding, and do not include theeffects of other forms of flooding such as from groundwater or artificial drainagesystems.Effects of climate change2.27 The fourth assessment report of the IPCC concluded that warming of theclimate is unequivocal 1 . There is a growing scientific consensus that thesechanges are expected to increase flood risk. In addition, climate change couldalso influence environmental and socio-economic factors such as nationalprosperity and social cohesion. The expected effects will most likely be feltfirst by the most vulnerable in society. While the different global emissionscenarios and climate-change models may lead to substantially differentpositions by the end of this century, the trends for the next 20-30 years do notdiffer significantly.2.28 Rising sea levels and more frequent and more severe coastal storms willsignificantly increase the risk of coastal and estuarial flooding as well as thatof coastal erosion. For example, the flooding that occurred in Dublin in 2002,when a 1 metre surge coincided with one of the highest spring tides of theyear, could change from a relatively rare to a more common occurrence.Assuming a correlation between the rate of sea-level rise and the rate of coastalerosion, the current rate of coastal erosion and the consequential economicimpacts of flooding are expected to multiply over the next century.2.29 The effects of increases in winter rainfall and in rainfall intensity will varybetween river catchments but floods are likely to become more severe andmore frequent.Planning Guidelines1 Inter-Governmental Panel on Climate Change (IPCC), 4th assessment report. “ClimateChange 2007”.