Surface water run-off
Surface water run-off is: 'Water flow over the surface of roofs and ground surface to a drainage system. Ground surface run-off occurs if the ground is impermeable, is saturated or if the rainfall is particularly intense.'
Volume of run-off is: 'The volume of run-off that is generated by rainfall occurring on the site. This is typically measured in cubic metres. Additional predicted volume of run-off is the difference between the volumes of run-off; pre-development, greenfield and post development.'
Ref Home Quality Mark One, Technical Manual SD239, England, Scotland & Wales, published by BRE in 2018.
NB Run-off coefficient is a measure of the amount of rainfall that is converted to run off.
A recurrence interval is: ‘The average time between runoff events that have a certain flow rate, for example, a flow of 2 m/s might have a recurrence interval of two years.’ Ref The SuDS Manual (C753) published by CIRIA in 2015.
Climate Change 2021, The Physical Science Basis, published by the Intergovernmental Panel on Climate Change in 2021, defines runoff as: ‘The flow of water over the surface or through the subsurface, which typically originates from the part of liquid precipitation and/or snow/ice melt that does not evaporate, transpire or refreeze, and returns to water bodies.’
[edit] Related articles on Designing Buildings
Featured articles and news
Professional practical experience for Architects in training
The long process to transform the nature of education and professional practical experience in the Architecture profession following recent reports.
A people-first approach to retrofit
Moving away from the destructive paradigm of fabric-first.
International Electrician Day, 10 June 2025
Celebrating the role of electrical engineers from André-Marie Amperè, today and for the future.
New guide for clients launched at Houses of Parliament
'There has never been a more important time for clients to step up and ...ask the right questions'
The impact of recycled slate tiles
Innovation across the decades.
EPC changes for existing buildings
Changes and their context as the new RdSAP methodology comes into use from 15 June.
Skills England publishes Sector skills needs assessments
Priority areas relating to the built environment highlighted and described in brief.
BSRIA HVAC Market Watch - May 2025 Edition
Heat Pump Market Outlook: Policy, Performance & Refrigerant Trends for 2025–2028.
Committing to EDI in construction with CIOB
Built Environment professional bodies deepen commitment to EDI with two new signatories: CIAT and CICES.
Government Grenfell progress report at a glance
Line by line recomendation overview, with links to more details.
An engaging and lively review of his professional life.
Sustainable heating for listed buildings
A problem that needs to be approached intelligently.
50th Golden anniversary ECA Edmundson apprentice award
Deadline for entries has been extended to Friday 27 June, so don't miss out!
CIAT at the London Festival of Architecture
Designing for Everyone: Breaking Barriers in Inclusive Architecture.
Mixed reactions to apprenticeship and skills reform 2025
A 'welcome shift' for some and a 'backwards step' for others.