Mechanisms of flooding in Cork City
Olbert, Agnieszka Indiana
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Olbert AI, Comer J, Nash S, Hartnett M (2015) Mechanisms of flooding in Cork City Proceedings of the 2015 National Hydrology Conference, Athlone, 17th November 2015
Flooding is one of the most frequent and devastating natural disasters. Many urban developments are located in estuaries where river flow and sea water merge. Cork City situated in the River Lee estuary frequently subject the extensive fluvial and coastal floods is one of such vulnerable locations. It is chosen in this study to investigate the roles of the flood mechanisms on the extent of urban inundation. This paper provides methodology for determination of mechanisms of urban flooding and their effects. Multiple drivers such as coastal and fluvial processes are considered to occur individually or jointly. In the assessment interactions and dependencies between flood drivers are also included and accounted for in joint probability analysis. The patterns of flood wave propagation are investigated to establish roles of the individual flood drivers. The analysis of flooding is a multistep process involving both probabilistic and deterministic modelling where probabilistic model provides inputs in terms of extreme sea water levels (coastal flooding) and river flows (fluvial flooding) as boundary conditions to deterministic coastal model which simulates flood wave propagation and ultimate extent of inundation. The MSN multi-scale nested ultra-high resolution numerical model is used to simulate 50- and 200-year extreme floods in urban area of Cork City. Results show that the mechanism of flooding plays a crucial role in flood characteristics and inundation pattern. While coastal flooding affects mostly downtown section of the city, fluvial flooding dominates initially city suburbs in the upper section of the river before channelling downtown through a network of east-west oriented streets and recreational area towards city centre.With regards to flood probabilities, coastal and fluvial defence systems in tidal section of the river are capable of protecting against 1 in 200-year coastal driven flood, while the river flows exceeding 50-year return period may solely cause flooding. Fluvial mechanism in Cork area is a critical driver of flooding and the most severe floods in Cork City result from extreme river flows combined with moderate-to-high sea water levels. The research allows to understand the mechanisms of flooding in Cork City, and by that to identify flood-prone areas for low-frequency high risk flood scenarios.