Project Overview

The Carrigtohill flood mitigation project was undertaken for the IDA to allow expansion of the current IDA Business Park, located in Cork. The current business park has tidal AADT’s of over 3,000 in peak hours and has a high pedestrian footfall. All works had to be completed in a restricted confined space to ensure there was no disruption to the business park users. Temporary traffic management phasing was fundamental for the successful delivery of the project. To ensure pedestrian access, which had to remain open at all times, several temporary footpaths where installed during the project.

Extensive earthworks were undertaken, which included the excavation of over 100,000m³ for the attenuation pond and attenuation tank, and disposal off-site of over 50,000m³. Silt mitigation measures were implemented to prevent silt from entering the adjacent stream and prevent rainwater entering the excavation. The project also involved the importation of over 1,000m³ of sand for the base of the crated attenuation system and of bulk drainage materials.

Over 3,000m³ of dredged material was excavated from two existing storage ponds to remove the silt build up. The dredged material was stored on-site within a bunded area to allow the material to dry out before being disposed of off-site. Strict environmental controls were implemented during the dredging works. This included over pumping the existing stream feeding the pond, allowing the pond to drain prior to undertaking the works. Three six-inch pumps were installed, along with one six-inch standby pump.

Works also included levelling the surrounding area with surplus topsoil to remediate the hollows that were causing ponding and, subsequently, isolated flooding. A new storm water drainage pipe, 1.5m in diameter and in excess of 4m deep, had to be laid up the east road within the IDA Business Park. The new storm alleviation overflow pipe of 1.5m diameter that was installed crossed an existing 900mm long water main. Following careful excavation and exposing the line and level of the existing water main, it was concluded that the new pipe could not be installed due to insufficient clearance and the risk of damaging the service. It was, therefore, proposed that the 1.5m single pipe would be replaced with two 900mm pipes, which would allow easier construction and more clearance beneath the existing water main. This proposal was accepted by the client and Irish Water and used in the final works.