Coastal And Tidal Flooding In The UK: How Sea Flood Risk Is Measured And Where It Is Rising
Coastal flooding happens when high tides and storm surges push the sea over the land. In England it is mapped together with river flooding, and sea level rise means once-a-century extreme sea levels are expected to become annual events by 2100.
What Is Coastal Flooding?
Coastal flooding is flooding from the sea. The Environment Agency describes it as flooding from the sea - where high tides and storm surges lead to coastal flooding.
Coastal flooding is different from coastal erosion. Flooding is water covering land temporarily; erosion is the permanent loss of land to the sea. England maps them separately, and a property can be at risk from one, both or neither.
What Is The Difference Between Tidal, Coastal And Sea Flooding?
Tidal, coastal and sea flooding are often used for the same thing: flooding caused by the sea rather than by rain or rivers. The official data mostly uses "the sea" as the source; Northern Ireland's maps use "tidal".
How the terms are used:
| Term | Usual meaning | In the official data |
|---|---|---|
| Sea flooding | Flooding from the sea | England's source label: "rivers and the sea" (combined band); Wales: "sea" (its own band) |
| Coastal flooding | Sea flooding at the coast | The Environment Agency's description of sea flooding |
| Tidal flooding | Sea flooding linked to tides | Northern Ireland's maps use "tidal" for the sea source |
| Coastal erosion | Loss of land to the sea | A separate map: the National Coastal Erosion Risk Map |
In England, the flood risk band for "rivers and the sea" combines both sources into one figure for each place. Wales and Northern Ireland publish separate levels for the sea.
What Causes Coastal Flooding?
Coastal flooding is caused by the sea rising above the land or the defences that protect it. The Environment Agency lists high tides and storm surges as the cause, and climate change is raising the baseline those events start from.
The main causes:
- High tides. Named by the Environment Agency as a cause of coastal flooding.
- Storm surges. Also named; flood alerts are issued for high tides, surges or strong winds at sea.
- Rising sea levels. Once-a-century extreme sea levels are expected to become annual by 2100; see how sea level rise changes coastal flood risk.
Surges are not a new danger. The Environment Agency's national assessment records that the 1953 North Sea surge caused hundreds of fatalities.
How Is Sea Flood Risk Classified?
Sea flood risk is classified differently in each UK nation, and the thresholds for the sea are lower than for rivers in planning. In England, Flood Zone 3 starts at a 0.5% annual chance for the sea but 1% for rivers.
| Nation | Classification | Sea threshold |
|---|---|---|
| England — Flood Zones | Flood Zone 3a | 1% or greater annual probability of river flooding, or 0.5% or greater of sea flooding |
| England — flood risk bands | Rivers and the sea combined | High: greater than 3.3% (greater than 1 in 30) |
| Wales — risk levels | Sea shown separately | Medium: between 1 in 200 (0.5%) and 1 in 30 (3.3%) |
| Scotland — SEPA | Coastal likelihoods | Medium: at least 0.5% chance of flooding each year |
| Northern Ireland — Flood Maps NI | Tidal probability | High 10% (1 in 10); Medium 0.5% (1 in 200); Low 0.1% (1 in 1000) |
The lower sea threshold applies in planning (Flood Zones in England, the Welsh sea levels, Northern Ireland's 1 in 200 year coastal flood plain). How England's zones and bands differ is explained in Flood Zones explained.
Where In The UK Is Coastal Flooding Most Common?
Coastal flooding affects coastal and estuary towns across the UK, but the official figures do not isolate it everywhere. The Environment Agency does not publish a separate count of properties at risk from the sea in England, because its band combines rivers and the sea.
What the published figures show:
- England. 2.4 million properties are in areas at risk from rivers and the sea, rising to around from 2.4 million to around 3.1 million, which is a 27% increase with climate change.
- Scotland. SEPA projects a 90% increase in the number of properties at risk of coastal flooding, 40% increase in the number at risk for river flooding and 25% for surface water flooding, so coastal flooding is where the steepest proportional rise is expected.
- Wales. Natural Resources Wales publishes sea flood risk as its own level, available per postcode.
Coastal towns' own figures are on each place page, ranked in most flooded towns in the UK.
What Is A Shoreline Management Plan?
A Shoreline Management Plan is a long-term plan for how each stretch of the English coast will be managed against flooding and erosion. There are 20 SMPs covering the English coast, setting out a planned approach to 2105, and each section of coast is given one of four management approaches.
| Approach | What it means |
|---|---|
| Hold the line | Maintain or upgrade protection from flooding or erosion by holding the shoreline in broadly the same position |
| Advance the line | Actively move shoreline defences significantly seawards |
| Managed realignment | Change the position of the shoreline in a controlled way, such as by slowing erosion or creating habitat to help manage flooding |
| No active intervention | Maintain or encourage a more natural coastline, which may involve discussing adaptation to flooding or erosion |
Source: Environment Agency, Shoreline management plans.
Two points matter to a coastal buyer:
- Plans depend on money. The Environment Agency states: "All are dependent upon funding being available."
- Plans affect planning. SMPs are used as part of the town and country planning system to designate Coastal Change Management Areas (CCMAs), which inform local plans and development decisions.
The approach for any stretch of coast is shown on the Environment Agency's Shoreline Management Plan Explorer. A home on a "no active intervention" or "managed realignment" section faces a different long-term future from one behind a "hold the line" defence.
How Will Sea Level Rise Change Coastal Flood Risk?
Sea level rise will make coastal flooding more frequent. The Environment Agency states that by 2100 extreme once-a-century sea-level events are expected to become annual, and that UK sea levels could rise by over a metre. The projections form a range, not a single figure.
The range in the Environment Agency's national assessment, all by 2100:
| Projection | Source |
|---|---|
| UK sea levels could rise by over a metre | Environment Agency |
| Once-a-century extreme sea levels become annual | Environment Agency |
| A global rise of 2 metres "cannot be ruled out" | Intergovernmental Panel on Climate Change, as cited by the Environment Agency |
Erosion rises with the sea. The National Coastal Erosion Risk Map shows up to up to 32,800 properties in areas at erosion risk by 2055 if Shoreline Management Plans are not delivered, and 19,700 properties by the end of the century even with them delivered.
How Do You Find Out If A Property Is At Risk Of Coastal Flooding?
A property's risk of coastal flooding is shown by entering its postcode into check the flood risk of any UK postcode, which gives the Flood Zone and the flood risk band that include the sea. For erosion and the long-term plan, check the coastal erosion map and the Shoreline Management Plan Explorer separately.
The full coastal check:
- Flood risk band and Flood Zone for the address, including sea flooding.
- Coastal erosion risk on the National Coastal Erosion Risk Map, for 2055 and 2105.
- The Shoreline Management Plan approach for that stretch of coast.
- Flood history from the seller and, in England, from the Environment Agency.
- Flood warnings. Coastal flood warnings cover high tides, surges or strong winds at sea; sign up through Floodline on 0345 988 1188.
Does Coastal Flooding Appear On A Flood Map?
Coastal flooding appears on every main UK flood map, but not always as a separate layer. In England it is combined with river flooding in both the Flood Zones and the flood risk bands; Wales, Scotland and Northern Ireland show it separately.
| Map | Coastal flooding shown |
|---|---|
| Flood Map for Planning (England) | Yes, in Flood Zones 2 and 3 combined with rivers |
| Check your long term flood risk (England) | Yes, in the "rivers and the sea" band |
| Flood Map for Planning (Wales) | Yes, as separate Sea Flood Zones |
| SEPA flood maps | Yes, coastal flooding as its own source |
| Flood Maps NI | Yes, as tidal flooding |
| National Coastal Erosion Risk Map (England) | No — erosion only |
Does Home Insurance Cover Coastal Flooding?
Home insurance covers flooding as a standard peril, which includes flooding from the sea, but the terms for coastal homes vary by insurer. The ABI states that Home insurance covers you against damage or loss to your property caused by a variety of perils such as fire, storm, flood, subsidence, burst pipes and water damage. Check the policy for storm, flood and any exclusions.
Points specific to the coast:
- Read the flood definition. Each policy defines flood in its own wording, which decides what a claim covers.
- Erosion is not flooding. Check how the policy treats land loss or subsidence caused by the sea.
- Flood Re covers eligible coastal homes built before 1 January 2009, on the same terms as anywhere else.
How premiums, excesses and refusals work is explained in flood insurance.
How Do You Protect A Property From Coastal Flooding?
A property is protected from coastal flooding by community defences first, and by property-level measures that keep water out or limit damage when defences are overtopped. What protection a stretch of coast will receive in future depends on its Shoreline Management Plan and funding.
The measures:
- Community defences. Sea walls, embankments and tidal barriers, maintained where the Shoreline Management Plan holds the line.
- Keeping water out. Flood doors, flood barriers and anti-flood air bricks, where water depth allows.
- Limiting damage. Resilience measures, such as raised electrical sockets, that reduce damage when water gets in.
- Planning ahead. Sign up for coastal flood warnings and know what to do; see what to do in a flood.
Costs and which measures suit which depth of flooding are in property flood resilience.
Sources (Verified 17 Sep 2026)
| Claim | Source |
|---|---|
| Sea definition; 1953 surge; 2.4m to 3.1m (27%); once-a-century annual; over a metre; IPCC 2 m; erosion 32,800 and 19,700 | Environment Agency, National assessment 2024 |
| 20 SMPs; to 2105; four approaches; funding; CCMAs; SMP Explorer | Environment Agency, Shoreline management plans |
| Flood Zone 3a sea threshold | Planning Practice Guidance |
| Welsh sea levels | NRW, Different types of flood risk |
| SEPA likelihoods; 90% coastal increase | SEPA flood maps FAQs · SEPA FRM plans FAQs |
| NI tidal probabilities | DfI, Contents of the Flood Maps NI |
| Flood alerts cover high tides, surges, strong winds | GOV.UK, Flood alerts and warnings |
| Flood as standard peril | ABI, Home insurance |
Frequently Asked Questions
What Causes Coastal Flooding In The UK?
Coastal flooding in the UK is caused by high tides and storm surges pushing the sea over the land. Rising sea levels mean extreme sea levels are expected to become far more frequent by 2100.
How Much Will Sea Levels Rise In The UK?
The Environment Agency states that UK sea levels could rise by over a metre by 2100, and that once-a-century extreme sea levels are expected to become annual. It also notes a 2 metre global rise by 2100 cannot be ruled out.
What Does "No Active Intervention" Mean On The Coast?
No active intervention is a Shoreline Management Plan approach that maintains or encourages a more natural coastline. It may involve discussing how to adapt to flooding or erosion, rather than building or maintaining defences.
Is Coastal Erosion Covered By Flood Insurance?
Coastal erosion is the loss of land, not flooding, so it is not the same as the flood peril in a home insurance policy. Check the policy wording on erosion, landslip and subsidence, and ask the insurer directly.