Does AL1 flood?

Yes — parts of the AL1 district carry real flood risk: 1 of its 11 at-risk postcodes reach the Environment Agency's High likelihood band. The AL1 postcode district covers Sopwell, Cunningham, Verulam, Bernards Heath, close to London Colney, Colney Street, Radlett, and surrounding villages in parts of Hertfordshire and England.

11 postcodes in the AL1 district appear in the Environment Agency's rivers-and-sea flood-risk dataset — worst bands: 1 high, 1 medium, 9 low. A postcode not listed here has no properties in any recorded risk band (which is good news, but never proof it cannot flood).

Free preview first · full report £19

Which AL1 postcodes are at risk?

AL1 1SF up to High AL1 1ST up to Medium AL1 1DG up to Low AL1 1DQ up to Low AL1 1HF up to Low AL1 1TX up to Low AL1 1XU up to Low AL1 2ES up to Low AL1 2HA up to Low AL1 2HE up to Low AL1 2HJ up to Low

Rivers and flooding history near AL1

The rivers that matter here, each monitored live on FloodRadar:

London Colney on the River Colne — 3.9 km away, highest on record 2.72m
Colney Street on the River Ver — 4.5 km away, highest on record 0.56m
Radlett on the Radlett Brook — 7 km away, highest on record 1.60m
North Mymms on the Mimmshall Brook — 8.1 km away, highest on record 2.35m

161 official flood warnings and alerts have been raised within ~10 km of the district's centre since 2006 (10 at warning level or above), most recently 27 August 2026. Warnings cover flood areas, not individual addresses.

Recorded flood extents near the district (Environment Agency record):

Ea06JanuaryWinter2026 (2026) — about 3.9 km from the centre
EA06FebruaryWinter2024 (2024) — about 1.6 km from the centre
January 2021 flooding — about 0.3 km from the centre
June 2020 flooding — about 1 km from the centre

Records, not floods: no outline on the record is not evidence a place has not flooded.

🏠 Buying or renting in AL1? The full property flood-risk report covers any postcode here — the official likelihood band, every recorded flood nearby with distances, warning history year by year, how the local rivers behave, and an insurance outlook, print-ready for £19. See what's in the report →

Flood risk in nearby postcode districts

AL2 AL3 AL4 AL5 AL6 AL8 AL9 AL10

Band = the worst likelihood band of any property in that postcode (EA Risk of Flooding from Rivers & Sea, defence-adjusted, area-level). Check any postcode in detail — or get the full £19 property report — at the property flood-risk report. © Environment Agency copyright and/or database right 2025. All rights reserved. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown Copyright and Database Rights 2025 OS AC0000807064. This product is produced in part from PAF® and Multiple Residence Data, the copyright in which is owned by Royal Mail Group Limited and/or Royal Mail Group plc. All rights reserved. Licence number AC0000807064.