How to Read the Flood Map for Planning

The Environment Agency’s Flood Map for Planning is one of the most important datasets in the English planning system. It determines when a Flood Risk Assessment is required, whether the Sequential Test and Exception Test apply, and what types of development are appropriate on a given site. Yet it is frequently misread, misunderstood, or over-relied upon — by developers, planning officers, and the public alike.

This article explains how to read the Flood Map for Planning correctly, what it does and does not tell you, and how to use it alongside other flood risk data to form an accurate picture of flood risk at a development site.

What Is the Flood Map for Planning?

The Flood Map for Planning (FMfP) is a dataset published by the Environment Agency that shows the extent of Flood Zones 2 and 3 across England. It is available as an interactive map on the GOV.UK website and as a GIS dataset that can be downloaded or accessed through the EA’s data services.

The FMfP is distinct from the Environment Agency’s other flood mapping products — particularly the “Check your long-term flood risk” service, which shows risk from rivers, the sea, surface water, and reservoirs for individual properties. The FMfP is the specific dataset used for planning purposes.

What the Map Shows

Flood Zone 3

Flood Zone 3 is shown in dark blue on the FMfP. It represents land assessed as having a 1% or greater annual probability of flooding from rivers (1 in 100 year or more frequent), or a 0.5% or greater annual probability of flooding from the sea (1 in 200 year or more frequent).

Flood Zone 2

Flood Zone 2 is shown in light blue. It represents land assessed as having between a 0.1% and 1% annual probability of flooding from rivers (between 1 in 1,000 and 1 in 100 year), or between 0.1% and 0.5% annual probability from the sea.

Flood Zone 1

Flood Zone 1 is not shown on the map because it covers everything that is not in Flood Zone 2 or 3. It represents land with less than a 0.1% annual probability of flooding from rivers or the sea.

Areas Benefiting from Flood Defences

The FMfP shows areas that benefit from flood defences as a hatched overlay. These are areas that would be in Flood Zone 3 without the defences but are protected by the defence to a specified standard. However, the flood zone designation remains — an area protected by a flood defence is still designated as Flood Zone 3 on the planning maps.

Flood Defences

The locations of flood defence structures (walls, embankments, barriers) are shown as a separate layer on the interactive map.

What the Map Does Not Show

Understanding the limitations of the FMfP is as important as understanding what it shows:

No Distinction Between Flood Zone 3a and 3b

This is one of the most significant limitations. The FMfP shows Flood Zone 3 as a single zone. It does not distinguish between:

• Flood Zone 3a (high probability) — where most development types can be considered, subject to the Sequential Test and Exception Test
• Flood Zone 3b (functional floodplain) — where development is severely restricted to water-compatible and essential infrastructure uses

The distinction between 3a and 3b is critical for planning purposes, as it determines what development is appropriate. This distinction must be determined from the LPA’s Strategic Flood Risk Assessment (SFRA) or from site-specific hydraulic modelling. The SFRA typically defines Flood Zone 3b as the area that would flood in a 1 in 20 year event (5% annual probability), although some LPAs use different return periods.

No Surface Water Flood Risk

The FMfP only shows flood risk from rivers and the sea. It does not show surface water (pluvial) flood risk, which is shown on a separate dataset — the “Risk of Flooding from Surface Water” maps.

This is a critical omission because surface water flooding is the most common source of flooding in the UK. A site in Flood Zone 1 (low risk from rivers and the sea) may be at significant risk from surface water flooding. The PPG makes clear that surface water flood risk must be considered in Flood Risk Assessments and in the determination of planning applications.

No Groundwater Flood Risk

The FMfP does not show groundwater flood risk. Groundwater flooding occurs when the water table rises above ground level, and it can be a significant issue in areas with chalk or limestone geology. Groundwater flood risk must be assessed using British Geological Survey data, local knowledge, and site-specific investigation.

No Sewer Flood Risk

The FMfP does not show sewer flood risk. Sewer flooding occurs when the public sewer system is overwhelmed, and it can affect any property connected to the sewer network. Sewer flood risk data is held by the water companies (the DG5 register) and is not publicly available as a map layer.

No Climate Change Projections

The FMfP shows current flood risk. It does not show how flood zones may change in the future due to climate change. Climate change is expected to increase peak river flows, raise sea levels, and increase rainfall intensity, all of which will expand the extent of Flood Zones 2 and 3.

For planning purposes, climate change is addressed through the climate change allowances applied in the Flood Risk Assessment, not through the FMfP itself. However, this means that the FMfP may significantly understate the future flood risk to a site.

No Account of Flood Defence Standard

While the FMfP shows areas benefiting from flood defences, it does not show the standard of protection provided. A flood defence that protects against a 1 in 100 year event provides a very different level of protection from one that protects against a 1 in 25 year event. The standard of protection must be determined from the EA’s asset information or from the LPA’s SFRA.

How to Read the Map: A Step-by-Step Guide

Step 1: Locate Your Site

Navigate to the Flood Map for Planning on GOV.UK and enter the site address or postcode. Zoom in to identify the site boundary.

Step 2: Identify the Flood Zone

Determine whether the site is in Flood Zone 1, 2, or 3. If the site straddles zone boundaries — which is common — note the proportion of the site in each zone and, critically, where the proposed development footprint sits relative to the zone boundaries.

Important: The flood zone of the developable area (where buildings will be constructed) is what matters, not the flood zone of the entire site. If the proposed buildings are entirely in Flood Zone 1 but the site boundary extends into Flood Zone 2, the flood risk implications are different from a site where the proposed buildings are in Flood Zone 2.

Step 3: Check for Flood Defences

Look for the hatched overlay indicating areas benefiting from flood defences. If the site benefits from a flood defence, note the location and type of the defence. This information will be needed for the Flood Risk Assessment.

Step 4: Check the Surface Water Maps

The FMfP only shows river and sea flood risk. You must also check the surface water flood maps to understand the full flood risk picture. The “Risk of Flooding from Surface Water” dataset is available on the same GOV.UK service.

Surface water flood risk is shown at three probability levels:

• High — 3.3% annual probability (1 in 30 year)
• Medium — 1% annual probability (1 in 100 year)
• Low — 0.1% annual probability (1 in 1,000 year)

A site in Flood Zone 1 (low river risk) but with high surface water flood risk may still require a Flood Risk Assessment and may face significant planning constraints.

Step 5: Check the SFRA

The LPA’s Strategic Flood Risk Assessment provides site-specific flood risk information that goes beyond the FMfP. The SFRA typically includes:

• The distinction between Flood Zone 3a and 3b
• Detailed flood level data
• Information about flood defences and their standard of protection
• Climate change flood extents
• Surface water and groundwater flood risk assessment
• Guidance on when FRAs are required and what they should contain

The SFRA is usually available on the LPA’s website, typically in the planning policy evidence base section.

Step 6: Request Product 4 Data

For sites in Flood Zone 2 or 3, or where surface water flood risk is identified, the most detailed flood risk data is available from the Environment Agency through its Product 4 data service. Product 4 is a package of flood data specific to a defined area, which typically includes:

• Detailed flood level information for a range of return periods
• Flood depth and extent information
• Modelling outputs (where detailed models exist for the area)
• Historical flood event information
• Information about flood defences

Product 4 data is provided free of charge for planning purposes and can be requested through the EA’s enquiry service. The standard response time is 20 working days, so requests should be made early in the project.

Common Misinterpretations

”The site is on the edge of Flood Zone 3, so it is probably fine”

Flood zone boundaries are derived from modelling and are inherently uncertain. A site on the boundary of Flood Zone 3 may be just above or just below the modelled flood level. Site-specific analysis — including surveyed levels and detailed modelling data — is needed to determine the actual flood risk. In some cases, a site on the edge of Flood Zone 3 may actually be at lower risk than some sites within Flood Zone 2.

”The site has not flooded before, so the flood zone must be wrong”

Flood zones represent probability, not history. A site in Flood Zone 3 has a 1% or greater annual probability of flooding — this does not mean it floods every year, or even every decade. A 1% annual probability event will, on average, occur once in 100 years, but it could occur in any year (or not at all for an extended period).

”The site is in Flood Zone 1, so there is no flood risk”

Flood Zone 1 means low risk from rivers and the sea. It does not mean no flood risk. The site may be at risk from surface water flooding, groundwater flooding, sewer flooding, or reservoir flooding — none of which are shown on the FMfP.

”The flood defence protects the site, so the flood zone does not apply”

A flood defence reduces the probability of flooding but does not eliminate it. Defences can be overtopped (when the flood exceeds the design standard) or breached (when the defence fails). The residual risk of flooding behind a defence must be assessed in the FRA, and the flood zone designation still applies for planning purposes.

”The map has not been updated recently, so it is out of date”

The EA updates the FMfP regularly — typically annually — incorporating new modelling data, updated flood defence information, and other improvements. However, the map is a national-scale product and may not capture local changes in flood risk (such as new development, altered watercourse channels, or local drainage improvements). Site-specific assessment is always needed for planning applications.

Using the Map in Practice

For Planning Applications

The FMfP is the starting point for determining:

• Whether a Flood Risk Assessment is required (sites in Flood Zone 2 or 3, or in Flood Zone 1 where the site is 1 hectare or more)
• Whether the Sequential Test applies (sites in Flood Zone 2 or 3)
• Whether the Exception Test applies (more vulnerable development in Flood Zone 3a, highly vulnerable in Flood Zone 2)
• What vulnerability classifications are appropriate on the site

For Site Acquisition

Before purchasing a development site, check the FMfP (and the surface water maps) to understand the flood risk constraints. Flood risk affects:

• What types of development are appropriate
• The cost of the Flood Risk Assessment and mitigation measures
• The likelihood of obtaining planning permission
• The insurance position for the completed development
• The marketability of the completed units

For Preliminary Screening

Aegaea’s site mapper tool provides a quick screening of flood risk and other environmental constraints based on the EA’s flood data and other datasets. This can be a useful starting point before commissioning a full Flood Risk Assessment.

Conclusion

The Flood Map for Planning is an essential tool for understanding flood risk in the planning system, but it is only the starting point. It shows river and sea flood risk at a broad scale, but it does not capture the full picture — surface water, groundwater, sewer risk, climate change, and the distinction between Flood Zone 3a and 3b are all outside its scope.

Reading the map correctly means understanding both what it shows and what it does not show, and supplementing it with additional data from the surface water maps, the SFRA, Product 4, and site-specific assessment.

At Aegaea, we help developers, landowners, and planning consultants interpret flood risk data and prepare Flood Risk Assessments that provide a comprehensive picture of flood risk. If you need help understanding the flood risk to your site, get in touch with our team.