Is my property at risk from flooding?

Areas at risk from tidal flooding

The following maps show an estimate for the maximum sea water levels around the Isle of Man likely to be reached with a retrurn period of 1 in 200 years (equivalent to a 0.5% probability of occurring in any year). The levels include an allowance of +0.45 metres for climate change by 2070, in accordance with the Isle of Man Flood Risk Guidance (Department of Transport, 2008).

Douglas Harbour	Douglas Prom	Laxey

Ramsey	Peel	Port Erin

Port St Mary	Carrick Bay	Castletown

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Sea Level Trends and Climate Change

Water levels around the coast (mean and extreme levels) are influenced by both eustatic (actual sea level trend) and isostatic (vertical land level movement) effects. The current best estimate for the combined effect of these trends on sea levels around the Isle of Man is around +3.5 mm/yr.

The Intergovernmental Panel on Climate Change (Fourth Assessment Report, 2007) suggests that sea levels will rise between 0.2 and 0.6 metres during this century. The range is based on data from several numerical climate models, each using several scenarios for future emissions (but excluding possible rapid dynamical changes in ice flow). How these global estimates might translate into the Irish Sea is not currently known.

Onshore Waves and Swell

Much of the Island’s coast is exposed to onshore wave action. Other locations, such as the promenades at Douglas, Laxey, Ramsey (South), Peel, Castletown and the coastal roads around Carrick Bay and Derbyhaven can suffer flooding due to waves breaking over the sea walls. Although water tends to drain back to sea after each large wave, sometimes the waves and swell (with suitable period) can effectively ‘pump’ water onshore. For example, during the storm surge on 1st February 2002, sea water levels were apparently enhanced by around 30cm at Laxey, 60cm at Port St Mary and 75cm at Douglas Promenade when compared with levels in nearby sheltered ports. At Gansey (exposed to a southerly swell which had been running for several days), sea water reached properties almost 2 metres above the interpolated mean high water level.

River Flow

In spate conditions, the amount of water the Island’s rivers pour into the harbours can add considerably to the volume of sea water transferred during each tidal cycle. The overall water level can be increased by the river water, especially upstream of restrictions (such as bridges) which may constrict the flow seawards.

Areas at risk from river flooding

As part of the Isle of Man Flood Risk Guidance programme (2008), the Department of Transport is developing a series of maps indicating areas at risk of flooding from the Island's main rivers. The 'flood risk maps' are based on topographical surveys and hydrological modelling to estimate areas likely to be at risk during a 1 in 100 year fluvial flooding event (including an allowance for climate change).

Maps are currently available for the Rivers Dhoo and Glass and their confluence into the Douglas River, the River Neb (from Glen Helen to its confluence with the Foxdale Stream near St John's and downstream to the sea at Peel), the Sulby River (from Sulby Glen to Ramsey), the Laxey River (and lower Glen Roy), the Silverburn River (from Grenaby through Ballasalla to Castletown harbour), the Colby River (from Colby Glen to the sea near Kentraugh) and the Dumb River (from Billown to Poyllvaaish). Other maps will be added as they become available.

Douglas River	Rivers Dhoo & Glass	Upper River Glass

River Neb	Sulby River	Laxey River

Colby River	Dumb River	Silverburn River

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Floodrisk maps in PDF format

Maps showing areas at risk of tidal/coastal and river/rainfall flooding can be downloaded in PDF format (below). Larger scale sub-area maps can be obtained from the Department of Infrastructure.

Downloadable Documents