Castletown Harbour Tidal Walls


Castletown is the ancient capital of the Isle of Man. Located on either side of the estuary of the Silverburn River, at the point where the estuary meets the Irish Sea. The town is dominated by the medieval Castle Rushen which dates from 1265. The harbour is predominantly used for mooring a large number of private boats and yachts. Plus, it is within a Conservation Area.

The existing flood defences reflect a typical inner harbour environment with low quay walls. During the winter storms of 2013/14, the water level exceeded the level of the quay walls and flooded residential and commercial properties in the area. Consequently, owners of properties within the flood risk areas cannot get insurance to cover flood damage.

Castletown Harbour was assessed by our team as being at risk of tidal flooding during the 1 in 10-year event. With global warming and rising sea levels, the harbour is predicted to flood during a 1 in 1-year event in a hundred years-time.


The Isle of Man Government asked us to assess the scale of the problem. We prepared outline design proposals for constructing flood defences. These would reduce the risk of flooding at the Island’s harbours and sections of coastline. Funding was made available to progress with a scheme to defend Castletown from a 1 in 200-year tidal event in the year 2115. The design involved the construction of raised harbour walls and set back walls to create a flood cell around the harbour. The new walls are being built high enough to prevent over topping during predicted high tide events. Floodgates are to be installed at locations where there are gaps in the walls. These will be closed during predicted high tide events.

As Castletown is a very scenic harbour, and located within a Conservation Zone, it was necessary to ensure the floodwalls were not overly visually intrusive. For this reason, the reinforced concrete walls have been clad with stone.


Once the scheme is complete, a school and ninety-five residential and commercial premises within the Castletown Harbour area will be protected from tidal flooding. Residents will no longer have the worry of waking up to flooded properties.

Want to know more

For more information on this project please contact Alec Dane or Graham Kenn. You can also find out more on our Coastal and Maritime Engineering web page.

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