100-year event
A 100-year event (or 100-year return period event) is an event that occurs (or is exceeded) on average once in every one hundred years (such as a storm, flood or rainfall event). This can also be expressed as 1 in 100 or 1:100.
For example, a 100-year storm is a storm that is likely to occur once every hundred years.
A ‘return period’ is an estimate of the likelihood of a particular event occurring. The return period of a rainfall event is the average time between events of at least a given magnitude.
Events can also be described by their ‘probability of occurrence’ (or frequency of occurrence) which is expressed as a percentage, or as 1 divided by the return period. The probability of occurrence of a 100-year event is 1%.
The ‘critical duration’ is the duration of the event for a specified return period event.
Ref CIRIA. 2015. C753. The SuDS Manual.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Center for Sustainable Landscapes
The first US building to achieve BREEAM Outstanding In-Use.
70 buildings from 70 years of Concrete Quarterly. Book review.
An early stressed-skin structure
Conserving the iron roof at the Albert Dock.
People, principles and performance
Delivering an infrastructure revolution.
The admissibility of evidence.
How many can you name? 37 anyone?
CIOB respond to the points-based system.
When is the weather considered 'exceptionally adverse'?
ECA backs call for a rolling programme of rail electrification.
What does 'curtilage' mean and why does it matter?
Our duty to prevent harm and protect each other.