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
Check out some of the best features and news from Designing Buildings as well as key stories from around the web.
Mayors are to be given planning call in powers
Mayors across England will be able to make the most important planning decisions.
The Master Builder: William Butterfield and his times. Book review.
Why construction can't afford to ignore the skills gap.
Building Safety Regulator, 19 August
Gill Kernick appointed Independent Chair of Residents’ Panel.
Connecting knowledge, technology and conservation
Building competence for the future of built heritage.
Building Regulations and Building Safety Act
CIOB publishes free advice for non-domestic clients.
Building Safety Newsletter from MHCLG.
An extraordinary record of steel engineering worldwide.
Households living near new pylons to save on bills.
ECA warns growth must not outpace grid capacity or skills.
The role of the client and decision making
CIOB response to built environment professions call for evidence.
Construction's sustainability reporting revolution
Tracking upfront embodied carbon with digital tools.