Using the Flood Map for Planning to establish a flood zone
The flood map gives you a zone and a dated extract. Here is how to read it, what it leaves out, and how to request the modelled data an assessment is actually built on.
The Flood Map for Planning tells you which flood zone a site falls in, and that single answer decides whether a flood risk assessment is required and whether the sequential test applies. Using the Flood Map for Planning properly takes about ten minutes: find the site, read the zone, download a dated extract, and then request the detailed modelled data that the assessment will actually be built on. The mistake is to stop after the second step and treat a screenshot as evidence.
What the service shows and what it leaves out
The service maps flooding from rivers and the sea. It shows Flood Zone 3, land assessed as having a high probability of flooding, Flood Zone 2 for medium probability, and by implication Flood Zone 1 as everywhere else. It also shows flood defences and the areas that benefit from them.
The zones are defined ignoring the presence of defences. That is deliberate, because a defence can fail or be overtopped, and planning policy wants the underlying risk visible. It is also why a site behind a substantial defence can appear in Zone 3.
What the service does not show matters as much.
- Surface water flooding, which is mapped separately on the long term flood risk service.
- Groundwater and sewer flooding.
- Climate change allowances, which are applied by the assessor rather than shown on the map.
- The split between Zone 3a and Zone 3b, which is usually made in the council's strategic flood risk assessment.
- Small watercourses and ordinary watercourses that have not been modelled.
A site can therefore be in Zone 1 on this map and still need a Flood Risk Assessment because of surface water risk, area or a critical drainage designation.
Reading the zones around your site
Search by postcode, address or grid reference, then zoom to the site and compare the mapped boundary with your red line. Three things to look at.
Where the zone boundary crosses the site, note which parts of the development fall in which zone, since the sequential approach applies within a site as well as between sites. Put the buildings in the lowest risk part, and say in the assessment that you did, because the sequential approach within a site is a point officers look for and applicants rarely make explicitly.
Where the site is close to but outside a zone, treat the boundary as approximate. National modelling is not survey-accurate, and levels on the ground decide the real answer.
Where defences are shown, look at whether the site is in an area benefiting from them, because that changes the residual risk discussion even though it does not change the zone.
Getting a dated extract for the application
Download the extract the service produces rather than taking a screen grab. It carries the date, the location and the version of the data, which is what an officer needs when checking that the search was current.
File it with the application and reference it in the assessment. Where the application takes months to determine, check the map again before submission, because the data is updated periodically and an extract from last year may no longer match.
Keep the reference details in the project record: date of search, grid reference, zone result, and who carried it out. Reading the Flood Map for Planning and what it leaves out covers the interpretation traps in more detail.
Requesting detailed modelled data
The online map is a screening tool. A flood risk assessment for a site in Zone 2 or 3 needs modelled levels, and those come from the Environment Agency as a detailed data request, commonly referred to as a product request.
| Information | Why the assessment needs it |
|---|---|
| Modelled flood levels for stated return periods | Sets finished floor levels and freeboard |
| Climate change scenarios | Applies the correct allowance for the epoch |
| Model node locations and extents | Shows how close the modelling is to the site |
| Historic flood outlines and records | Evidence of what has actually happened |
| Defence details, standard and condition | Informs residual risk |
Requests take time, and charges may apply, so raise the request at the start of the project rather than when the assessment is being written. Check the current turnaround and fees before you build a programme around them.
Where no detailed model exists for a watercourse, the assessment has to say so and use another method, which the Environment Agency and the lead local flood authority will want to agree.
Where the map and the council's assessment disagree
The council's strategic flood risk assessment refines the national picture using local modelling. It may map Zone 3b functional floodplain, apply climate change allowances, identify critical drainage areas and set out local policy expectations.
Where the two differ, the council's document usually governs the way policy is applied in that area. Use both: the national map for the zone and the dated extract, the strategic assessment for the local refinement and for what the authority expects to see.
If your own modelling produces a different result again, that is a legitimate position to argue, and it needs to be evidenced, agreed with the Environment Agency where possible, and set out clearly rather than slipped into an appendix.
Disagreements of that kind are more common than you might think on small watercourses, where national modelling is coarse or absent. A topographical survey tied to ordnance datum is usually the first thing that moves the discussion, because it replaces an assumed ground level with a measured one.
Recording the search and checking again
- Search the site and record the date, grid reference and result.
- Download and file the dated extract.
- Run the surface water check on the long term flood risk service and file that too.
- Read the council's strategic flood risk assessment for the site.
- Submit the detailed data request early if the site is in Zone 2 or 3.
- Repeat the map search immediately before submission and note the result.
Number three is worth doing even where the site is plainly in Zone 1 and well under a hectare. Surface water risk is the most common flooding problem on small sites, and a council drainage officer who sees the check in the pack is far less likely to ask for more.
Step six takes two minutes and occasionally saves an application. Data updates move boundaries, and an assessment written against superseded mapping is the kind of thing an objector's consultant enjoys finding.
Where a site also carries heritage constraints, the flood evidence and the heritage case have to work together, since raising floor levels on a listed building is rarely straightforward and a Heritage Statement will have to address any change to the building's appearance.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.
PlanScope checks Environment Agency flood data as part of its constraint detection and drafts the report structure, with the detailed modelling and the professional judgement supplied by your assessor. Enter your postcode on PlanScope to see which reports your site needs.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Does the Flood Map for Planning show surface water flooding?
No. It maps flooding from rivers and the sea. Surface water risk is shown on the separate long term flood risk service, and groundwater and sewer flooding are not mapped nationally at all. A site can sit in Flood Zone 1 on the planning map and still carry high surface water risk across part of it.
Why is my site in Flood Zone 3 when it sits behind a flood defence?
Because the zones are defined ignoring the presence of defences. Planning policy wants the underlying risk visible, since defences can fail or be overtopped. The service shows separately which areas benefit from defences, and that information feeds the residual risk section of an assessment rather than changing the zone.
What evidence of the flood zone should accompany an application?
The dated extract the service produces, not a screen grab, filed with the assessment and referenced in it. The extract carries the date, location and data version, which lets the officer confirm the search was current. Repeat the search immediately before submission and record the result.
How do I get modelled flood levels for a site?
Through a detailed data request to the Environment Agency, which supplies modelled levels for stated return periods, climate change scenarios, model extents, historic flood outlines and defence details. Requests take time and charges may apply, so raise them at the start of the project rather than while writing the assessment.
What if the council's strategic assessment shows something different?
The council's strategic flood risk assessment refines the national picture with local modelling, including the Zone 3b functional floodplain and critical drainage areas, and it usually governs how policy is applied locally. Use the national map for the zone and the extract, and the strategic assessment for local refinement.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.