Photo: Christopher Hilton · CC BY-SA 2.0In Chelmsford, heavy rain puts more homes at risk than rivers or the sea: 3.9%, against 2.5%
On the Environment Agency’s maps, which allow for flood defences, “high or medium” means at least a 1 in 100 chance of flooding from rivers or the sea in any year. Chelmsford’s Hazard risk Grade is C−: #69 of 81 in Essex.
What stands out about Chelmsford’s hazards
From the Environment Agency’s maps and records and the BGS radon atlas, below.
What Chelmsford faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Rivers and the sea
Surface water
Past floods
The River Can
Flood warnings
Radon
Chelmsford grades C− for hazard risk
Flood risk from rivers and the sea, against all UK towns.
The share of homes at high or medium risk from rivers and the sea, ranked against every UK town of 1,000 or more: fewer homes at risk is better. Towns with none at high or medium risk are ordered by their share at low risk, so they don’t all share one score. Surface water and radon aren’t graded: they are described below.
Where the water goes in Chelmsford
Turn layers on and off. Blue is the risk from rivers and the sea; pink is where heavy rain collects. Both allow for flood defences.
The river and sea risk follows the Wid, the River Wid and the River Can. Surface-water risk is spread across the city, in dips, underpasses and along small streams, which is why more homes are exposed to it.
2.5% of Chelmsford’s homes are at high or medium risk from rivers or the sea
The Environment Agency’s national map, allowing for defences. A further 1.8% are at low risk.
Share of each UK town’s homes at high or medium risk from rivers and the sea. 35% of UK towns have none; Chelmsford has more than 82% of towns.
| # | Town | People | High or med. | |
|---|---|---|---|---|
| 1 | Oldham Greater Manchester | 110,722 | 0% | |
| 2 | Birkenhead Merseyside | 109,854 | 0% | |
| 3 | Kensington and Chelsea London | 143,348 | under 0.1% | |
| … | ||||
| 56 | Hastings East Sussex | 91,497 | 2.1% | |
| 57 | Worthing West Sussex | 111,635 | 2.4% | |
| 58 | Chelmsford Essex | 110,612 | 2.5% | |
| 59 | Weston-super-Mare Somerset | 84,600 | 2.7% | |
| 60 | Blackpool Lancashire | 149,087 | 2.7% | |
| … | ||||
| 66 | Lincoln Lincolnshire | 104,553 | 6% | |
| 67 | Grimsby Lincolnshire | 85,915 | 8.9% | |
UK towns of 77,000 to 155,000 people.
The Environment Agency’s Risk of Flooding from Rivers and Sea (NaFRA2, June 2026) counts each postcode’s homes by band; the shares weight those postcodes by Census 2021 households. The EA counts include homes built since 2021.
Heavy rain puts about 1.6 times as many Chelmsford homes at risk as rivers and the sea do
Surface water is rain that falls faster than drains and the ground can take it. It is mapped separately from rivers and the sea, and it is not in the Hazard risk Grade.
About 1.8% of homes are at high risk of surface-water flooding (a 1 in 30 chance or more each year) and 2.1% at medium risk: roughly 1,820 households. A further 6% face a low risk from surface water. That is more than 56% of UK towns.
Our estimate: every address in the city (ONS NSUL) read on the Environment Agency’s Risk of Flooding from Surface Water map (NaFRA2, 2025), each postcode’s share weighted by its Census 2021 households. Neither agency publishes a count of homes for surface water, so treat it as a guide; one street can differ from the next.
Chelmsford has flooded in 3 recorded years since 1947, most of all in 1947
Every flood the Environment Agency has mapped inside Chelmsford’s built-up area, newest first. The record is fullest for big river floods; small and surface-water floods are often missing.
- 2009January 2009: River flooding recorded7 hectares inside today’s built-up area
- 1958June 1958: The sea came in15 hectares inside today’s built-up area
- 1947February 1947: River flooding recorded28 hectares inside today’s built-up area
Floodwater covered 28 hectares of what is now Chelmsford in 1947, the largest flood the record holds here (February).
436 of Chelmsford’s households today live inside the outline of a recorded flood.
Since 1947, the largest recorded flood inside the city covered 15 hectares.
The River Can in February 2026 rose to its 2nd-highest level since 1990
The highest level each winter (October to September) at the Environment Agency’s Beach's Mill gauge, since 1990. The river normally runs between 0.14 m and 1.57 m here.
- 24 November 20142.39 m
- 7 February 20261.99 m
- 4 January 20151.97 m
- 14 October 20141.95 m
- 16 February 20261.93 m
- 13 December 20231.72 m
The River Can has topped its normal range on 12 days since 1990, most in the winters of 2014–15 and 2025–26. By its highest day, the winter of 2025–26 was the 2nd-highest of the 31.
Environment Agency Hydrology API, Beach's Mill (station E22889), daily maximum level; the record and normal range from the EA’s stage scale. Live river levels are on GOV.UK’s Check for flooding.
No flood warning or alert is in force for Chelmsford · 54 warnings in 20 years
The Environment Agency has 5 flood warning areas and 3 alert areas reaching into the city; warnings since the service began in 2006.
The warning area covering the most of Chelmsford, The Rivers Can and Chelmer, through Chelmsford, has not had a flood warning since 2006. Of the 54 warnings, 28 were for The River Wid from Ingatestone, to and including, Writtle and 14 for Riverside properties on the Rivers Chelmer and Can in Chelmsford.
2012 had the most warnings (16); 2024 the most alerts (18). The most recent warning was on 17 November 2022.
Show the 8 warning and alert areas
| Area | Kind | Since 2006 | Now |
|---|---|---|---|
| The River Wid from Ingatestone, to and including, Writtle | Warning area | 28 | None |
| Riverside properties on the Rivers Chelmer and Can in Chelmsford | Warning area | 14 | None |
| The River Chelmer from Churchend to the Rivermead Industrial Estate in Chelmsford | Warning area | 6 | None |
| The River Chelmer from the A138 at Chelmsford to Maldon | Warning area | 6 | None |
| The Rivers Can and Chelmer, through Chelmsford | Warning area | 0 | None |
| The Rivers Wid and Can | Alert area | 122 | None |
| The upper River Chelmer | Alert area | 29 | None |
| The lower River Chelmer, including the River Ter and brooks around Sandon | Alert area | 26 | None |
Environment Agency Historic Flood Warnings (first issues only, not updates; “flood watch” counted as an alert before 2011) and the real-time flood-monitoring API. Sign up for free warnings on GOV.UK or call Floodline, 0345 988 1188.
Chelmsford is in the lowest radon band
Radon is a natural radioactive gas from the ground; long exposure raises the risk of lung cancer. The atlas gives the chance that a home in each 1 km square is above the UK action level (200 Bq/m³).
Every 1 km square over Chelmsford is in the lowest band: fewer than 1 in 100 homes are expected to be above the action level.
BGS/UKHSA Indicative Atlas of Radon in Great Britain, version 3. Check an address at UKradon.org.
Flood risk in the places around Chelmsford
Share of homes at high or medium and at low risk from rivers and the sea. Tap a town for its page.
| Town | People | High or medium | Low | Hazard |
|---|---|---|---|---|
| Chelmsford | 110,612 | 2.5% | 1.8% | C− |
| Writtle | 4,703 | 0.2% | 0.3% | B− |
| Broomfield | 3,491 | 0.3% | 0% | B− |
| Galleywood | 6,410 | 0% | 0% | A |
| Boreham | 3,561 | 0% | 0% | A |
| Little Waltham | 1,038 | 1.8% | 6.3% | C− |
| Danbury | 6,196 | 0.2% | under 0.1% | B− |
| Stock | 1,573 | 0% | 0% | A |
Chelmsford has more homes at high or medium risk than any neighbour in the table. Galleywood, Boreham and Stock have none.
Get ready for what Chelmsford faces
Free warnings, what to do in a cloudburst, and what to check before you move.
- Sign up free for Environment Agency flood warnings by text, call or email.
- Floodline: 0345 988 1188, 24 hours.
- Chelmsford’s warning areas include The Rivers Can and Chelmer, through Chelmsford and The River Chelmer from the A138 at Chelmsford to Maldon.
- Surface water rises in minutes, often with no warning issued: stay out of underpasses and dips.
- Keep the gullies and drains outside your home clear of leaves.
- Report a blocked road drain to the council.
- Never walk or drive through floodwater: 30 cm of moving water can float a car.
- Move valuables, papers and medicines upstairs.
- Turn off gas, electricity and water if you’re told to.
- Check the address on GOV.UK’s long-term flood risk service: it gives rivers and sea and surface water separately.
- Ask whether the home has flooded or had a flood insurance claim; the TA6 property form asks the seller.
- Homes built before 2009 can get flood cover through Flood Re, the government-backed scheme; newer homes can’t.
What this data can and can’t tell you
- Defences are counted. Both agencies’ maps allow for flood defences and the chance they are overtopped or fail, so a town behind a defence scheme can show few homes at high risk and many at low risk.
- Surface water is our estimate. Neither agency publishes a count of homes at risk from surface water, so we read each address on the map. A flat on a hill and a basement in a dip can share a postcode.
- Past floods are what was recorded. The flood outlines come from surveys, aerial photographs and reports; many small floods, and most surface-water floods, were never mapped.
- One town, many streets. Risk is street by street. Check a specific address on GOV.UK’s long-term flood risk service before you buy or rent.
Questions about flooding and hazards in Chelmsford
Does Chelmsford flood?
The last flood the Environment Agency recorded inside the city was in January 2009. 2.5% of homes are at high or medium risk from rivers and the sea on the Environment Agency’s maps, which allow for flood defences. About 3.9% of homes are at high or medium risk from surface water, when heavy rain overwhelms the drains. Chelmsford grades C− for hazard risk against UK towns.
Which parts of Chelmsford are at risk of flooding?
From rivers and the sea, the places the Environment Agency warns directly: The River Wid from Ingatestone, to and including, Writtle, Riverside properties on the Rivers Chelmer and Can in Chelmsford, The River Chelmer from the A138 at Chelmsford to Maldon and The River Chelmer from Churchend to the Rivermead Industrial Estate in Chelmsford. Surface water can collect in low spots anywhere in the city. Check a specific address on GOV.UK’s long-term flood risk service.
When did Chelmsford last flood?
The recorded flood outlines inside the city run from 1947 to 2009 (3 years); the largest was in 1947. Flood warnings have been issued for parts of the city since 2006, most recently on 17 November 2022.
Is Chelmsford at risk of surface water flooding?
About 1.8% of homes are at high risk and 2.1% at medium risk from surface water, against 2.5% at high or medium risk from rivers and the sea. Surface water floods come with little warning, and the agencies don’t issue warnings for them.
Is radon a problem in Chelmsford?
Not by the atlas: every 1 km square over Chelmsford is in the lowest band, where fewer than 1 in 100 homes are expected to be above the action level.
Are there flood warnings in Chelmsford now?
No flood warning or alert was in force near Chelmsford at 13 November 2026, 22:58. Live warnings are on GOV.UK’s Check for flooding service and Floodline, 0345 988 1188.
Contains Environment Agency information © Environment Agency and/or database right 2026. Contains British Geological Survey materials © UKRI 2026.
Sources: Environment Agency Risk of Flooding from Rivers and Sea, postcodes in areas at risk (June 2026); Natural Resources Wales Flood Risk Assessment Wales (May 2026); ONS Census 2021 households by postcode · Environment Agency Risk of Flooding from Surface Water (NaFRA2, 2025) and Natural Resources Wales Flood Risk Assessment Wales surface water and small watercourses, read at every address (ONS National Statistics UPRN Lookup, September 2026) and weighted by Census 2021 households by postcode · Environment Agency Recorded Flood Outlines and Natural Resources Wales historic flood map, inside the ONS 2022 built-up-area boundary · Environment Agency Hydrology API (daily maximum river level) and flood-monitoring stage scales · Environment Agency real-time flood-monitoring API · Environment Agency Historic Flood Warnings (January 2006 to June 2026) and flood warning and alert areas · BGS/UKHSA Indicative Atlas of Radon in Great Britain, version 3, by 1 km square · TownRatings grades: our own summary of the data, ranked against UK towns only. All under the Open Government Licence v3.0.
Contains public sector information licensed under the Open Government Licence v3.0. Contains HM Land Registry data © Crown copyright and database right 2026. Contains OS data © Crown copyright and database right 2026 (ONS boundaries). Northern Ireland: Source: NISRA; contains Land & Property Services data and Ordnance Survey of Northern Ireland information, © Crown copyright, licensed under the Open Government Licence v3.0. Scotland: contains National Records of Scotland data, Registers of Scotland data and SEPA data, © Crown copyright / © SEPA 2025, licensed under the Open Government Licence v3.0.