Flood Map for Planning Wales: Flood Zones Explained

The Flood Map for Planning Wales is the official map used to assess flood risk in the Welsh planning system. Produced by Natural Resources Wales (NRW), it shows where land is at risk of flooding from rivers, the sea, and surface water or small watercourses, and it sorts that land into flood zones by the annual probability of flooding. Planning authorities use it to screen a site and decide whether a development needs a Flood Consequences Assessment before permission can be granted.

One point sets it apart from the equivalent map in England: the Welsh flood zones already build in climate change, and they are drawn assuming no flood defences are in place.

The Flood Map for Planning shows the potential extent of flooding over the next century, and it deliberately ignores existing defences so the underlying floodplain is never hidden.

What is the Flood Map for Planning Wales?

The Flood Map for Planning is NRW's national map of flood risk, and it is the map the Welsh planning system actually relies on. It underpins Technical Advice Note 15 (TAN15), the Welsh Government guidance on development, flooding and coastal erosion that supports Planning Policy Wales and Future Wales.

It replaced the older Development Advice Map on 1 December 2021. After that date the Development Advice Map held no weight in planning decisions, so any older assessment still quoting it is out of date. The map is refreshed twice a year, in late May and late November, as NRW improves its modelling and flood data.

The map offers two views. The Basic view is a high-level screen for TAN15, answering the first question a planner asks: does this site fall in a mapped flood zone at all? The Detailed view carries the modelled information used to prepare a Flood Consequences Assessment. NRW is the statutory consultee on flood risk in the Welsh system, and understanding how NRW reviews planning applications helps explain why the map matters so much at the screening stage.

You can view the map through NRW's Flood Map for Planning service, with the supporting technical guidance alongside it.

The two Welsh flood maps: Flood Map for Planning vs Flood Risk Assessment Wales

Wales has two flood maps, and confusing them is one of the most common early mistakes on a development site. The Flood Map for Planning is the official planning tool. The Flood Risk Assessment Wales (FRAW) map is the public-facing map most people find first when they search for their address, and it has no formal role in planning at all.

NRW is blunt about the distinction.

Together the two maps make up the Wales Flood Map, but only one of them speaks to a planning application. If you are checking whether your house might flood, the FRAW map is the right tool. If you are assessing a development site, screening for the risk-based approach, or preparing evidence for NRW and the local planning authority, the Flood Map for Planning is the one that counts.

What the Flood Map for Planning shows: the map layers

The map is not a single picture. It is a set of layers you can switch on individually or view together, each showing a different source or aspect of flood risk. Screening a site properly means checking every relevant layer, rather than only the headline rivers-and-sea view.

• Rivers and sea flood zones: Flood Zones 2 and 3 mapped for fluvial (river) and tidal (sea) flooding, viewable separately or combined.
• Surface water and small watercourses: a separate layer for pluvial flooding and for the smaller channels that river modelling does not always capture.
• TAN15 Defended Zones: land sitting behind flood defences that meet a defined standard, shown separately because the flood zones themselves assume no defences.
• Recorded flood extents: the outlines of areas that have flooded in past recorded events, useful context that does not itself set a planning flood zone.
• Supporting layers: flood defence locations, main rivers, reservoir flood risk and shoreline management information, which add detail around the core zones.

Flood Zone 1 is not drawn on the map. It is simply the land that falls outside the mapped Flood Zone 2 and Flood Zone 3 areas. The map also has blind spots. It does not cover groundwater, sewer flooding, or the hidden risk that comes from mining and quarrying legacy, and those sources have to be assessed separately. The sources of flood risk run wider than any national map, and unusual cases such as quarry and mine-water flood risk in Wales fall outside the mapped zones entirely.

Flood zones on the Flood Map for Planning Wales

The Flood Map for Planning divides land into three flood zones based on the annual probability of flooding from rivers, the sea and surface water. A lower zone number means a lower chance of flooding in any given year. Because the probabilities are expressed as small percentages, they are often described as return periods instead, such as a 1 in 100 chance. The thresholds differ slightly between river and coastal flooding.

Two things are easy to miss. First, every threshold above already includes the effects of climate change, so the zones are drawn for the future rather than today's climate. Second, the zones assume no flood defences, which is why a site protected by a defence can still sit inside Flood Zone 3.

More than a 1 in 100 chance of river flooding in any year, including climate change, places a site in Flood Zone 3 — the highest-risk zone under the Welsh system.

Flood Zone 1 — low probability of flooding

Flood Zone 1 is land with less than a 0.1 per cent annual probability of flooding from rivers or the sea, which is less than a 1 in 1,000 chance in any given year. Most development is acceptable here in principle, and the planning system steers development towards it. Even so, surface water and drainage still need thought, because a low river-and-sea risk does not rule out flooding from other sources.

Flood Zone 2 — medium probability of flooding

Flood Zone 2 covers land with an intermediate chance of flooding: between 0.1 and 1 per cent a year from rivers or surface water, and between 0.1 and 0.5 per cent a year from the sea. Development can still be acceptable, but planning authorities usually expect a Flood Consequences Assessment showing the flood consequences can be managed safely across the lifetime of the development.

Flood Zone 3 — high probability of flooding

Flood Zone 3 is the highest-risk zone: more than a 1 per cent annual chance from rivers or surface water, or more than 0.5 per cent from the sea. This is the main floodplain, and the tightest controls apply here. Highly vulnerable development, which includes most housing, is heavily restricted, and new housing on undeveloped land in Flood Zone 3 should not normally be permitted. How the vulnerability of a development interacts with its flood zone is the heart of the Welsh policy test.

TAN15 Defended Zones on the map

A TAN15 Defended Zone is an area that benefits from flood defences managed or maintained by a Risk Management Authority to a defined standard. To qualify, the defences must provide at least a 1 in 100 standard against river flooding, or a 1 in 200 standard against coastal flooding. These zones are mapped as a separate layer precisely because the flood zones themselves are drawn as if no defences existed.

A defended zone is not a safe zone. Defences can be overtopped in a larger event than they were designed for, and they can fail or be breached, so a residual flood risk always remains behind them. A development in a defended area still has to show that its flood consequences would be acceptable over its whole lifetime. This is also why a site can stay in a high flood zone even after new defences are built: the zone reflects the underlying floodplain, not the protection in front of it.

Why the Welsh flood zones already include climate change

This is the single biggest difference between the Welsh and English maps, and it catches out people who work across the border. In England, the base flood zones on the Flood Map for Planning show present-day risk, and climate change is shown through separate layers. In Wales, the flood zone extents already incorporate climate change projections over roughly the next century.

The practical effect is that a Welsh flood zone is drawn for a wetter, higher-sea-level future by default. A detailed Flood Consequences Assessment still applies specific climate change allowances to the modelling, but the screening zones themselves are not a snapshot of today.

Assume nothing based on the English map. The Welsh flood zones are broader by design because they build in climate change, so a site can screen differently on either side of the border.

If you usually work in England, read the two systems side by side. The English flood zones run on the National Planning Policy Framework and the Sequential and Exception Tests. Wales runs on TAN15 and the Flood Consequences Assessment.

How to check which flood zone a site is in (Wales)

For most sites, checking the flood zone is the first practical step in assessing whether a development is feasible and what evidence it will need. The map does the screening; a specialist confirms what it means for the specific plot.

1. Open the Flood Map for Planning and search the site. Enter the address or grid reference on NRW's Flood Map for Planning service and locate the red-line boundary.
2. Read the Basic view first, then the Detailed view. The Basic view tells you quickly whether any part of the site falls in Flood Zone 2 or 3; the Detailed view carries the modelled information you would need for a Flood Consequences Assessment.
3. Check every relevant layer. Look at rivers and sea, surface water and small watercourses, and the TAN15 Defended Zones layer, rather than the combined view alone. A site can be clear on rivers but flagged on surface water.
4. Cross-check other records. Compare against the public FRAW map and any local flood history, remembering the map does not cover groundwater, sewers or ground levels.
5. Decide whether a Flood Consequences Assessment is required. If any part of the site sits in Flood Zone 2 or 3, or in a Defended Zone, the TAN15 rules on when an FCA is needed will usually apply, and the assessment has to show the development can remain safe for its lifetime.

Frequently asked questions about the Flood Map for Planning Wales

Getting a site checked in Wales

The Flood Map for Planning Wales is the starting point, not the finish line. It tells you which zone a site sits in and whether flood risk needs to go further. A planning decision rests on showing that flood consequences can be managed safely over the lifetime of the development. Where a site falls in Flood Zone 2 or 3, or behind a defence, that evidence comes through a Flood Consequences Assessment. Unda prepares TAN15-compliant Flood Consequences Assessments for sites across Wales, and can tell you quickly whether your site is likely to need one. Talk to our consultants or start a quote to discuss it.