SuDS Rainwater Attenuation Sizing Chart

In the UK SuDS attenuation assessments are typically completed on a site by site basis.

The key inputs for the attenuation volume calculation is the design storm inflow and the allowable discharge rate. The design storm is location dependant and varies across the UK.  The allowable dicharge rate again varies from local lead flood authority but 1 l/s appears the most common value offered by the LLFA for small residential developments.

We have completed an excercise assessing attenuation volumes for 25 sites in the UK reflecting the various water company locations.

The base design scenario assumptions are: 

• 1 in 100 year design rainfall return period
• 40% climate change
• 1 l/s allowable discharge
• Orifice Flow control and Fixed Outflow (floating orifice) have been calculated
• 100m2 roof area
• Location as per the Water Company below

Get in touch today to complete your attenuation or soakaway sizing calc.