Protecting Cork City – Ireland’s largest flood relief scheme

Combining measures to protect Cork from flood risks

While developing the design, the multidisciplinary team – including engineers, scientists, architects and planning advisors – carried out an extensive analysis of all the possible upstream and downstream options. After analysing the causes of previous flood events, it was clear that a combination of flood protection measures would be required to protect Cork city today as well as being adaptable for the future challenges posed by climate change.

The proposed scheme incorporates significant biodiversity enhancements in rural areas and public parks, whilst urban plazas and riverside walkways throughout will cast the River Lee as a central character, woven into the daily lives of locals and visitors. Innovative flood defence elements will blend in with the surrounds: built-in benches along the riverfront will offer a space for leisure while doubling up as defences in combination with demountable, tilt-up barriers during floods.

Through close collaboration with the ESB (Electricity Supply Board), the existing hydroelectric dam operation will be further optimised to improve flood risk management. This integrated catchment approach will work in combination with other flood defence measures, including low-level defences and washlands.

The revised management system for the dams will reduce the peak flows potentially reaching the city by almost 40%, enabling the required quayside defences to be minimised. These low-level defences are being designed to perform their flood defence function well into the future. The designation of washlands as part of this scheme will involve using areas of existing floodplain to ensure that the capacity of the reservoirs is maximised.

A flow control structure at the head of the southern channel will be used to rebalance flows between the north and the south channels to better match their respective capacities, thus reducing the risk and minimising the requirement for defences.

Harnessing digital tools to optimise flood defences

Arup with partners, JBA Consulting, calculated the design flows of the river by building an integrated continuous simulation model to predict rainfall patterns and river flows over a theoretical 1,000-year period – the first time such a hydrological approach has been adopted on a flood relief scheme in Ireland.

By modelling the ground-water regime in the city, Arup’s geologists, hydrogeologists and scientists ensured that all possible flow paths were determined and considered, with suitable protection measures incorporated. In line with international best practice, the scheme is being designed to provide protection against the 1-in-100-year fluvial and 1-in-200-year tidal flood events.

As this scheme covers such a large area, maximising the benefits for local residents and businesses is being prioritised throughout the design. Beyond protecting against flood risks, the proposed scheme involves upgrading and regenerating riverfront areas of the city, with seamlessly integrated defence measures providing new urban spaces for people to enjoy.