Update on Dollymount Flood Defence after Project Meeting – 05/11/15

Just posting up some updates here as promised after a robust meeting on the above scheme with DCC project officials this morning.

(1) Wall Height – 4.25m OD (“above sea level”)

This is made up of 4 elements:

  • Current tide levels
  • An associated wave height of 0.25m (reduced from 0.75m on account of the presence of the Bull Island)
  • An allowance for a rise in sea levels of 0.5m due to global warming which should cover the next 30-40 years as per OPW standard (0.09m rise in Clontarf in the last 15 years alone)
  • A “free-board” of 0.3m as per OPW standard.

The 4.25m OD is the coastal defence standard across the City’s defences.

(2) Loss of Visual Amenity

Once the project is complete and relevant paths/roadways have been raised:

  • The maximum wall height that pedestrians/cyclists will have to look over is 1.138m (including wall capping)
  • Motorists will be 0.15m lower as pedestrians/cyclists are raised above road level

(3) The “Do Nothing” option at St Annes Park i.e. let the James Larkin road flood

DCC has vlsual records of floods occurring @ this location. If the sea breaches the wall at this location the water will start to work its way towards the Bull Wall and residential/commercial properties are then at risk.

(4) The use of glass panels in a sea defence

Not considered robust enough to withstand the pounding of the sea – more detail to follow once available.

(5) Finish of the wall

Proposals for a better finish to the wall are to be brought to the December North Central Area Committee.

(6) Loss of Visual Amenity for Motorists

DCC will estimate the length of the loss of amenity for motorists – I’ll post it up here as soon as it becomes available. DCC will examine the possibility of raising the road levels to compensate and will present their assessment at the December North Central Area Committee.