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.
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• 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.