Floodplain
A floodplain is land adjacent to a watercourse over which water flows or would flow in times of flood, if defences were not in place.
The flood zone area classification system devised by the Environment Agency refers to:
- Flood Zone 1: Land outside the floodplain. There is little or no risk of flooding in this zone.
- Flood Zone 2: The area of the floodplain where there is a low to medium flood risk.
- Flood Zone 3: The area of the floodplain where there is a high risk of flooding.
Ref The HS2 London-West Midlands Environmental Statement, Department for Transport, November 2013.
NB Culvert, screen and outfall manual, (CIRIA C786) published by CIRIA in 2019, defines a floodplain as: ‘Land on either side of a river that is below the highest defined flood level.’
The National Flood and Coastal Erosion Risk Management Strategy for England, Glossary, published by the Environment Agency in 2020, suggests a floodplain is: ‘Land with a high probability of being partly or wholly covered with water during flooding from rivers or the sea – ignoring the presence of flood defences.’
[edit] Related articles on Designing Buildings
- Applying flood resilience technologies GG 84.
- Building flood resilience.
- Catchment flood management plans.
- Coastal defences.
- Dyke.
- Environment Agency.
- Flood.
- Flood and Water Management Act.
- Flood defences.
- Flood insurance.
- Flood mapping key to future development in Wales.
- Flood risk.
- Flood risk assessment.
- Flood risk management plans.
- Floodplain capacity.
- Floodscape.
- Functional floodplain.
- Future flood prevention.
- Pitt Review.
- River engineering.
- Sustainable urban drainage systems.
- Thames barrier.
- Water engineering.
Featured articles and news
Applications and benefits of acoustic flooring
From commercial to retail.
From solid to sprung and ribbed to raised.
Strengthening industry collaboration in Hong Kong
Hong Kong Institute of Construction and The Chartered Institute of Building sign Memorandum of Understanding.
A detailed description fron the experts at Cornish Lime.
IHBC planning for growth with corporate plan development
Grow with the Institute by volunteering and CP25 consultation.
Connecting ambition and action for designers and specifiers.
Electrical skills gap deepens as apprenticeship starts fall despite surging demand says ECA.
Built environment bodies deepen joint action on EDI
B.E.Inclusive initiative agree next phase of joint equity, diversity and inclusion (EDI) action plan.
Recognising culture as key to sustainable economic growth
Creative UK Provocation paper: Culture as Growth Infrastructure.
Futurebuild and UK Construction Week London Unite
Creating the UK’s Built Environment Super Event and over 25 other key partnerships.
Welsh and Scottish 2026 elections
Manifestos for the built environment for upcoming same May day elections.
Advancing BIM education with a competency framework
“We don’t need people who can just draw in 3D. We need people who can think in data.”
Guidance notes to prepare for April ERA changes
From the Electrical Contractors' Association Employee Relations team.
Significant changes to be seen from the new ERA in 2026 and 2027, starting on 6 April 2026.
First aid in the modern workplace with St John Ambulance.
Solar panels, pitched roofs and risk of fire spread
60% increase in solar panel fires prompts tests and installation warnings.
Modernising heat networks with Heat interface unit
Why HIUs hold the key to efficiency upgrades.