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Two-dimensional flood and sediment transport modelling and risk mapping

The primary objective of this project was to further develop Arup’s expertise in two-dimensional (2D) flood and sediment transport modelling of coastal systems.  The research used a case study approach.

The case study adopted was Cloughaninchy beach in County Clare, Ireland which suffered severe coastal erosion and flooding during a significant storm event in January 2014.  Several numerical models were developed to understand the key mechanisms of flooding at the site and to assess the risk of flooding from tidal, wave overtopping and fluvial sources: (a) a MIKE 21 spectral wave model of the nearshore and offshore area, (2) a MIKE 21 FM coastal flood model, and (3) a 1D river hydraulic model. A separate coast line evolution model was also developed which was used to understand the risk of erosion at the site. The risk of wave overtopping was assessed using a detailed methodology developed specifically for the study.

Significant areas of Cloughaninchy beach are at risk of flooding for both the current and mid-range future scenarios. Several residential properties are at risk from wave overtopping while large areas of agricultural land are at risk from both tidal and fluvial sources. The shoreline is at risk of erosion in the mid- and future range future scenario events. The study also illustrated that funding for engineering works in relatively rural coastal areas can be hard to justify due to cost.

As part of the study a detailed methodology was developed to estimate the risk of flooding from wave overtopping. The methodology adopted can also be used by Arup engineers for other coastal modelling projects. The site-specific findings of the study were used to inform on engineering options to address flood risk and coastal erosion at Cloughaninchy beach.

Our findings contribute to the understanding of flood risk in Ireland.  The results of the research clearly illustrate the risk associated with wave overtopping, a source of flooding which may otherwise be over-looked. The study highlights the urgent need for a policy document on the provision of coastal defences for coastal areas that are not heavily populated.