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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 postcode of the Water Company below

Get in touch today so we can share provisional attenuation volumes for your project.

1 Affinity Water
2 Albion Water Ltd
3 Anglian Water Services Ltd
4 Bournemouth Water Ltd 
5 Bristol Water plc
6 Cholderton & District Water Company Ltd
7 Dwr Cymru Cyfyngedig (Welsh Water)
8 Hafren Dyfrdwy
9 Independent Water Networks
10 Leep Water Networks Limited
11 Northumbrian Water Ltd
12 Portsmouth Water plc
13 Severn Trent Water Ltd
14 Scottish Water 
15 South East Water Ltd
16 South Staffordshire Water plc
17 South West Water Ltd
18 Southern Water Services Ltd
19 SSE Water Ltd
20 Sutton & East Surrey Water plc
21 Thames Water Utilities Ltd
22 United Utilities Water plc
23 Veolia Water Projects Limited
24 Wessex Water Services Ltd
25 Yorkshire Water Services Ltd


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