Flood risk across Hertfordshire
Hertfordshire's chalk streams feed the Lea and the Colne. River flooding is generally confined to narrow valley floors, but surface water from heavy rain affects towns right across the county, and groundwater can rise in the chalk valleys after very wet winters.
Flood zones only show river and sea flooding, and they ignore flood defences. Surface water and reservoir risk aren’t part of the zones – check them on the Environment Agency’s long-term flood risk service, or get the full report, which covers every source.
Rivers that shape local flood risk
Main rivers are managed by the Environment Agency. Smaller watercourses and drainage are the responsibility of Hertfordshire County Council and landowners.
River Lea – Harpenden, Hertford, Ware and the Lee Valley
River Colne – Watford and Rickmansworth
River Ver – St Albans
River Gade and River Bulbourne – Hemel Hempstead and Berkhamsted
River Stort – Bishop's Stortford and Sawbridgeworth
Who manages flood risk here
Hertfordshire County Council is the Lead Local Flood Authority, responsible for surface water, groundwater and ordinary watercourses. The Environment Agency manages main rivers and the sea, and issues flood warnings. Your district or borough council decides planning applications – and asks for a flood risk assessment in Flood Zones 2 and 3.
Getting a written answer for an address
The free check describes the area around your postcode. For a specific property, the full report checks your exact address against every flood dataset and gives you a dated PDF to share with your surveyor, conveyancer or insurer.
For planning decisions, your local council has the final say.
