A third Cork reservoir would not alleviate city flooding

A third Cork reservoir would not alleviate city flooding
Pedestrians negotiate the tidal flooding on Trinity pedestrian bridge in February. Pic; Larry Cummins

CREATING a third reservoir on the River Lee would not alleviate flooding in Cork, according to the Office of Public Works.

The suggestion had been mooted on several occasions by members of the public who have criticised the current OPW plans for flood defences in Cork.

Interest groups had suggested an upstream reservoir to slow the flow of water to the city centre in a bid to minimise the construction of high quay walls in Cork.

The proposed location was on the Lee upstream of the Carrigadrohid reservoir.

On behalf of the OPW, Arup engineers explored the option, concluding that it would have minimal impact on the city centre and would result in greater spend on the project overall.

Engineers identified a potentially suitable site just upstream of Dromcarra Bridge, 7km southwest of Macroom.

The area in question had not been considered as part of the Lee CFRAMS study upon which Arup were instructed to base their flood defence proposals.

As such, the potential use of the area as a reservoir had not been considered in preparation of the flood plans.

The engineers' report claimed that the scheme would have involved the construction of a 200-metre embankment, the relocation of the current road surface, several compulsory purchase orders and integration with the other dams on the river, totalling somewhere in the region of €15-20 million.

It concluded that the proposed location is too far upstream to have a major impact on the city centre.

The report stated, “As the proposed area is located relatively far upstream in the catchment and immediately upstream of two larger controlled reservoirs at Inniscarra and Carrigadrohid, it was recognised that whilst there was a potentially significant storage volume available, its upstream location would likely limit any benefit in terms of flow reduction seen in Cork.” Arup claimed that the reservoir would result in the reduction of flood levels by up to 300mm in height which, they added, is not enough to warrant the exclusion of the new quay walls planned for the city.

"As these defences are generally set back from the river walkways and are in the order of 1.8m to 2m high, it is considered that this reduction would not fundamentally alter the scale and nature of the defences," the report noted.

The potential creation of a new reservoir will be kept on file as part of a contingency plan in the face of climate change, though Arup deemed it too expensive and too inefficient to pursue, the report concluded.

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