Challenging the Flood Map for Planning with evidence
If you think the Flood Map for Planning puts your site in the wrong Flood Zone, you can ask the Environment Agency to look again through an evidence review request, a GOV.UK process published on 21 September 2026. It accepts three kinds of evidence: new or updated modelling, survey of small areas, and records of real floods.
Real model output: a 1-in-100-year flood, plus 29% for climate change, spreading across the Hamstall Ridware floodplain in the first-generation 2022 model; 149 ha at its peak. Replayed, not to time scale. A study model of one village, not a Flood Zone. How to read this: drag the slider to move through the flood.
Animated map: in the 2022 model of a 1% AEP flood with a 29% climate allowance, water spreads over 79 hours to cover 149 hectares of the River Blithe and Trent floodplain at Hamstall Ridware, Staffordshire.
- kinds of evidence the Environment Agency accepts in an evidence review request
- 3
- the largest area a topographic survey on its own can correct
- under250m²
- GOV.UK published the evidence review request process
- 21 Sep2026
- 1-in-100-year flow at Hamstall Ridware from pooled analysis, against 30.0 from the gauge record alone
- 44.6m³/s
About the author. Hisham Nuhu is a UK-based flood and disaster risk specialist. He worked at England’s Environment Agency from 2019 to 2025 and holds an MSc in Water Science, Policy and Management from the University of Oxford. He works remotely or in-country with governments, development banks, UN agencies and consulting firms, and in England with councils, communities, landowners and developers.
How do I challenge a Flood Zone in England?
Contact the Environment Agency about the location, then submit an evidence review request with new evidence. It checks its own planned updates first, assesses your evidence against its technical standards and decides whether to use it. Surface water maps are different: you raise those with the lead local flood authority, usually your county or unitary council.
The route was set out on GOV.UK on 21 September 2026. It covers Flood Zones, Risk of Flooding from Rivers and Sea and the other national flood risk products. Coastal erosion and reservoir flood maps have their own submission details, by email to the Environment Agency.
An evidence review request in six steps
Check the map and the data
Look up the site on the Flood Map for Planning and order the detailed data, Product 4. Product 4 is sent within 20 working days.
Talk to the Environment Agency
Raise the location. It checks its published products and any planned updates first. A known data issue may already be in hand.
Build the evidence
New or updated modelling, survey of a small area, or recorded floods. A model of lower quality than the existing one may not be used.
Data sharing agreement
You agree one before your evidence can be used in published products.
Review
The Environment Agency reviews the evidence and may ask for changes. Incorporating it “may take several months”.
Maps updated
Accepted evidence goes into the national maps after the Environment Agency’s own processing. The final map may differ from your model.
How to read this: the steps light up in turn; tap or tab to any step to read it.
Sources
Environment Agency: Flood and coastal risk products: submit an evidence review request (GOV.UK, 21 September 2026); Flood risk assessments: applying for planning permission (GOV.UK). Schematic based on public sources.
What evidence does the Environment Agency accept?
Only three kinds: new or updated flood modelling; topographic survey of small areas, under 250 m², where ground levels are wrong; and recorded flood information, for Flood Zone products only. A model of lower quality than the existing one may not be used, and areas where land-raising is planned but not finished cannot be put forward.
| Evidence | When it helps | What it needs | Limit set by GOV.UK |
|---|---|---|---|
| New or updated modelling | The model behind the map is old or coarse, or misses a structure or a changed channel | Sound hydrology, survey and a model at least as good as the existing one; where the map uses a local model, the Environment Agency may provide it for you to update | “if your model is of lower quality or condition than the existing model, we may not use it” |
| Topographic survey | Ground levels in the map are wrong over a small area | A survey of that area | Small areas only, “less than 250 sqm” |
| Recorded flood information | Real floods contradict the mapped zone | Dated records of where the water reached | “for flood zone products only” |
Data sharing agreementYou must agree one before the Environment Agency can use your evidence to update its published products.
Land-raisingModel or survey evidence is not accepted for areas where changes such as land-raising are planned but not yet completed.
Holding commentIf your model is accepted, a holding comment may appear on some public services until the maps are updated.
Is my Flood Zone actually wrong?
Sometimes, but less often than people hope. Flood Zones ignore defences, so land behind a wall can rightly sit in Flood Zone 3. They can be wrong where the ground model misses a bank, the hydrology understates big floods, or a channel has changed. GOV.UK itself says a correction is “rarely needed for planning decisions”.
That last point matters. Planning authorities rely mainly on the site-specific flood risk assessment, which builds on and refines the Flood Map for Planning. If what you need is planning permission, a good assessment may get you there faster than a change to the map.
A challenge makes most sense when the land is clearly higher than the map assumes, when the model behind the map predates new survey or a changed channel, or when the hydrology rests on a gauge that cannot see the biggest floods. That last case is the one I know best.
Why can a gauge record understate the flood?
Because some gauges cannot measure the floods that matter. At Hamstall Ridware the weir is bypassed above about 13–14.5 m³/s, so the biggest floods go round it and the record flattens. The gauge alone gave 30.0 m³/s for the 1-in-100-year flood. Pooled analysis of similar catchments gave 44.6.
Look at the right-hand end of the chart. The largest annual floods bunch together instead of climbing, because above the bypass flow the gauge sees only part of the water. A map built on that record alone would draw the flood too small.
Fifty years at the village gauge: the record flattens where floods bypass the weir
How to read this: each dot is one year’s highest flow, with rarer floods to the right. The shaded band is where water starts to go round the weir. Switch the pooled estimate on and off to see the gap.
Annual maximum flows at NRFA station 28002, Blithe at Hamstall Ridware, 50 water years from 1959/60 to 2020/21, with a Gumbel fit; the pooled estimate for the whole catchment is from my flood estimation record (2025).
Sources
Gauge data: NRFA station 28002 © UKCEH; Environment Agency. My analysis.
Show the 50 annual maximum flows as a table
| Water year | Annual maximum flow, m³/s |
|---|---|
| 1959/60 | 17.10 |
| 1960/61 | 17.30 |
| 1961/62 | 7.88 |
| 1962/63 | 2.74 |
| 1963/64 | 10.70 |
| 1968/69 | 17.30 |
| 1969/70 | 11.60 |
| 1970/71 | 23.70 |
| 1971/72 | 14.60 |
| 1972/73 | 7.70 |
| 1973/74 | 12.50 |
| 1974/75 | 8.56 |
| 1975/76 | 2.92 |
| 1976/77 | 20.10 |
| 1977/78 | 11.80 |
| 1978/79 | 16.80 |
| 1979/80 | 15.20 |
| 1980/81 | 15.40 |
| 1981/82 | 18.80 |
| 1982/83 | 15.40 |
| 1983/84 | 13.50 |
| 1984/85 | 9.72 |
| 1985/86 | 17.40 |
| 1994/95 | 19.80 |
| 1995/96 | 2.50 |
| 1996/97 | 9.07 |
| 1997/98 | 17.80 |
| 1998/99 | 15.50 |
| 1999/00 | 9.79 |
| 2000/01 | 22.00 |
| 2001/02 | 11.40 |
| 2002/03 | 17.40 |
| 2003/04 | 11.40 |
| 2004/05 | 9.49 |
| 2005/06 | 4.31 |
| 2006/07 | 16.10 |
| 2007/08 | 13.80 |
| 2008/09 | 13.20 |
| 2009/10 | 6.68 |
| 2010/11 | 3.76 |
| 2011/12 | 18.70 |
| 2012/13 | 18.10 |
| 2013/14 | 12.20 |
| 2014/15 | 4.34 |
| 2015/16 | 14.30 |
| 2016/17 | 10.20 |
| 2017/18 | 13.50 |
| 2018/19 | 9.30 |
| 2019/20 | 21.90 |
| 2020/21 | 19.70 |
Neither extreme was right. The gauge misses the biggest floods. ReFH2, a rainfall–runoff method, does not know the reservoir is there, so it comes out high. I split the catchment at Blithfield Reservoir, routed the flood from above it through the reservoir, and scaled ReFH2 hydrograph shapes to the pooled peaks for each of four sub-catchments.
Three standard methods, three answers for the same rare flood
How to read this: each bar is one method’s estimate of the peak flow for the whole catchment. Switch between the 1-in-100 and 1-in-1,000-year flood; tap a bar to read it.
Whole-catchment checks from my flood estimation record v4 (2025). The design flows themselves were built for each of four sub-catchments.
| Estimate | 1 in 2 years | 1 in 100 years | 1 in 1,000 years | Method |
|---|---|---|---|---|
| Gauge record | 13.5 | 30.0 | 39.7 | Single-site statistics from the village gauge (FEH) |
| Pooled (WINFAP) | 17.7 | 44.6 | 58.3 | Pooled statistics from similar gauged catchments (FEH, WINFAP) |
| ReFH2 | 25.8 | 65.0 | 98.9 | ReFH2 rainfall–runoff model |
What modelling does a challenge need?
A model at least as good as the one behind the map, built on sound hydrology, survey of the channel and its structures, and good ground data, and checked against a real flood where one was recorded. Where the map uses a local model, the Environment Agency may provide it for you to update.
At Hamstall the 2024 model linked Flood Modeller in the channel with TUFLOW on the floodplain, on a 5 m grid built from 1 m LiDAR, with a surveyed channel and bridge. The hydrology was entirely my work; I built the 1D–2D model jointly with an Environment Agency modelling colleague. I checked the first-generation model against residents’ records of the February 2020 flood.
If you mean to use the same model for a planning application, it has to meet two sets of rules. GOV.UK says the requirements for modelling in a flood risk assessment are different from those for an evidence review request.
How do I get the Environment Agency’s flood data?
Through the Flood Map for Planning and your local Environment Agency office. Product 4, a detailed flood risk assessment map, is ordered online for the site and sent within 20 working days. Model reports, outputs and inputs, Products 5, 6 and 7, are requested by email from the local office.
| Product | What it is | How to get it |
|---|---|---|
| Product 1 | A copy of the flood map: Flood Zones 1, 2 and 3, defences, main rivers and water storage areas | Download from the Flood Map for Planning |
| Product 4 | A detailed flood risk assessment map: detailed flood data, defence details, past floods, modelled flood levels and breach hazard, where available | Order on the Flood Map for Planning page for the site; sent within 20 working days |
| Product 5 | Flood modelling and hydrology reports | Email request to the local Environment Agency office |
| Product 6 | Model output data, with the Product 5 reports | Email request to the local office |
| Product 7 | Model input data, with the Product 5 reports: “the best available modelled data we have for the area” | Email request to the local office |
| Product 8 | Flood defence breach hazard information | Included in Product 4 where available |
Product 3 has been discontinued; its information is now in other products.
How long does a challenge take?
Longer than most people expect. Building the evidence takes weeks or months, depending on whether a model already exists. Then, in GOV.UK’s words, incorporating new evidence “may take several months”, because it is reviewed, accepted and processed in stages. An accepted model may show as a holding comment before the maps change.
If the Flood Zone changes, do I still need a flood risk assessment?
Often, yes. A flood risk assessment is triggered by more than the river and sea Flood Zone: for example, any site of 1 hectare or more in Flood Zone 1 needs one. And because the modelling requirements for an assessment differ from those for an evidence review request, a model used for both must meet both.
How would you approach a challenge for my site?
In four steps, so you do not pay for modelling that cannot change the answer: a scoping call; a data request to the Environment Agency; a short go or no-go note on whether a challenge is likely to succeed, or whether a flood risk assessment would serve you better; then the evidence itself, to the Environment Agency’s standards.
From 2023 to 2025 I gave delivery support to two Environment Agency river models that update the Flood Map for Planning, one of them the Beverley Brook in south London: scope, programme, delivery tracking, quarterly finance and audit. That showed me what a model update involves from the client’s side.
The modelling on my own record is Hamstall’s: the hydrology entirely mine, the 1D–2D model built jointly with an Environment Agency modelling colleague.
Questions people ask
Can you guarantee the Flood Zone will change?
No. The Environment Agency decides whether evidence can be incorporated, and its final maps may differ from your model because of its own processing. If I think a challenge is unlikely to succeed, the go or no-go note will say so.
Who do I contact about surface water flood maps?
Your lead local flood authority, usually the county or unitary council. The evidence review request route covers Flood Zones, Risk of Flooding from Rivers and Sea and the other national river and sea products.
What is the Flood Map for Planning?
The Environment Agency’s online map of flood risk for planning in England, at flood-map-for-planning.service.gov.uk. It tells you whether you need a flood risk assessment, and you can download a map or order detailed flood data there.
We plan to raise the ground. Can we challenge the map first?
Not through an evidence review request: the Environment Agency cannot accept model or survey evidence for areas where changes such as land-raising are planned but not yet completed. Raising ground in a floodplain also raises the question of flood risk elsewhere.
Is the Hamstall model a Flood Zone?
No. It is a flood study model of one village. I use it to show how hydrology and modelling evidence are built, not as a Flood Map product.
Sources
- Environment Agency (2026). Flood and coastal risk products: submit an evidence review request. GOV.UK, published 21 September 2026. The evidence accepted, what to expect, the data sharing agreement and the contact details.
- Environment Agency (2026). Flood risk assessments: applying for planning permission. GOV.UK. Products 1 to 8, and when a flood risk assessment is needed.
- Environment Agency. Flood map for planning. GOV.UK service.
- Defra and Environment Agency (2023). Using modelling for flood risk assessments. GOV.UK.
- UK Centre for Ecology & Hydrology. National River Flow Archive, station 28002: Blithe at Hamstall Ridware.
- UK Centre for Ecology & Hydrology. Flood Estimation Handbook and ReFH2.
Work with me
Is your site in the wrong Flood Zone?
Send me the site address, what you want to do with the land and anything you have from the Environment Agency. I will reply with a scope, a fixed fee and a timescale, starting with whether a challenge is worth it. I don’t take on work on cases I handled while at the Environment Agency.