Freeboard

Culvert, screen and outfall manual, (CIRIA C786) published by CIRIA in 2019, defines freeboard as: ‘An allowance for uncertainty in design water level and any other physical processes that may affect the ability of an asset to withstand the design water level such as wave action or superelevation.’

See also Residual uncertainty allowance.

Containment systems for the prevention of pollution, Secondary, tertiary and other measures for industrial and commercial premises (CIRIA C736), published by CIRIA in 2014 defines freeboard as: ‘An allowance in the form of increased height of a containment wall for additional capacity over and above the minimum design requirement.’

Rules of Thumb, Guidelines for building services (5th Edition) BG 9/2011, by Glenn Hawkins, published by BSRIA in 2011, defines freeboard as: ‘The vertical distance in a water tank between the maximum water level and the top of the tank’. This definition is repeated in BG 87/2024, Useful Information Guide, written by Chin Hang “Kay” Lam and published by BSRIA in 2024.

High Speed Rail (Crewe – Manchester) Environmental Statement, Glossary, abbreviations and references, published by the Department for Transport in 2022, defines freeboard allowance as:

The height from the maximum design level of a watercourse to:

• the adjacent banks of an open channel, to provide a factor of safety against flooding; or
• the soffit (underside) of any culvert or bridge above, to reduce the risk of blockage by floating debris, etc.’

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