Flood defences, involving the construction walls up to 1.5m higher than the current coastal promenade, and rock armour up to 15m wide on the beach, are being proposed to protect Sandymount in South Dublin.
More than 20 years since the coastal suburb was hit by extreme flooding, Dublin City Council has published plans for defences on the beach and promenade along Strand Road, from the Merrion gates to Sean Moore Park, a distance of just over 2km.
Defences are needed to protect more than 1,000 homes in Sandymount identified at risk of flooding since 2002. However, their construction has been beset by delays.
The council has published four options to protect “people, property and infrastructure to the greatest extent possible” from “wave overtopping and coastal flooding”, Gerry O’Connell the council’s senior engineer with responsibility for flood protection said.
The first option involves construction of a new seawall which would be about 5m wide and 1.2m in height, on the seaward side of the existing promenade. The would be accompanied by a “large amount” of new rock armour or “revetements”, large boulders which would extend from 10m to 15m in width, being placed on the beach for part of the 2km length.
The second option would see similar revetements installed, but running continuously along the entire length of the beach. In addition to being 10m to 15m wide, the rock armour could reach about 1m above the height of the existing promenade.
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The third option would also be for a continuous revetment, but it would be stepped. The top of step would incorporate a path that could be up to 10m wide to reduce wave over topping at the road. The existing rock armour would be removed and replaced with the concrete steps. The top of the new revetment could be 1.5m higher than the existing promenade level.
The fourth option involves putting additional sand on the beach to create a higher and wider beach in front of the seawall. “The larger beach acts as a natural coastal defence absorbing the wave energy before it reaches the seawall which reduces flood risk and protects the existing seawall from wave impact,” O’Connell told councillors on Monday.
Extensive repairs to the existing seawall would likely be required and “groynes” timber structures, which would stretch out towards the sea for about 65m out from the existing sea wall would also be built.
This would be “quite a large increase in the level of the existing beach area. Also, with this, there would be significant maintenance on the structure of this size and significance,” O’Connell said.
“But it would be considered more environmentally friendly, possibly than some of the other options.”
Several councillors asked why a cycle route was not included in any of the four options.
Plans for a cyclepath on Strand Road were the subject of a five-year legal challenge which was resolved last year when the Court of Appeal overturned a High Court judgment that had blocked the implementation of the six-month trial of the path on the roadway.
However, there has been no progress on the development of the cyclepath in the road, which would have involved reducing the width of the carriageway and making it into a one-way route for traffic.
O’Connell said while the flood defence plans did not include provision for a cycleway they “would not conflict” with the development of a cycleway by the council’s traffic department in the future.
The four options will be presented to Sandymount residents later this month. The final option is expected to be selected early next year, with a planning application for the work due to be submitted by the start of 2028. The work could be completed by 2030, O’Connell said.
Costs for the project were not yet available, he said.