Sustainable Drainage Systems (SuDS)

We have extensive experience undertaking field testing using large scale soakaway tests in accordance with BRE365 (trial pits) and falling head permeability testing in accordance with BS5930 (boreholes) in relation to Sustainable Drainage Systems (SuDS). This work is often focused towards achieving a design that ensures surface water runoff is infiltrated to ground.

SuDS make use of the natural landscape to control the flow of surface water and reduce the risk of flooding, via the use of ponds, swales, green spaces, permeable paving and soakaway chambers. Whilst the style and purpose of each design can vary, they are generally designed in compliance with the SuDS Manual (CIRIA 743) and all have common purpose, which is to reduce run off to formal (piped) drainage systems and mitigate the flow of surface waters following development.



The intent to control surface water run and potential flooding exists within Schedule 3 of the Flood and Water Management Act 2010. From 7th January 2019 this becomes law and new residential development of more than one property or non residential construction area of 100m2 or greater will be required to manage surface water collection, attenuation and disposal on site.

As part of the new regulations, SuDS will be required to address the collection/disposal of surface water and surface water run off (e.g. hydraulic control).

Statutory approving bodies (SABs) within every Local Authority are responsible for approving drainage plans for proposed schemes. SAB and planning applications will run concurrently; SABs will have seven weeks to determine applications for schemes not requiring specialist consideration; proposed development will require both SAB and Planning approval. Pre-application discussions should be undertaken to ensure awareness of requirements and site limitations. The Sustainable Drainage System Standards for Wales identifies the five levels of priority for the SuDS will be considered, as outlined below:

Surface water runoff destination for Sustainable Drainage Systems

  • Priority Level 1: Surface water runoff is collected for use [most desirable];
  • Priority Level 2: Surface water runoff is infiltrated to ground;
  • Priority Level 3: Surface water runoff is discharged to a surface water body;
  • Priority Level 4: Surface water runoff is¬†discharged to a surface water sewer, highway drain, or another drainage system;
  • Priority Level 5: Surface water runoff is discharged to a combined sewer [least desirable].

SABs will also be tasked with enforcement action in the event SuDS applications are not submitted appropriately or are not constructed as per authorised details. The current guidance can be found here.

We recently assisted a national housing developer consider the feasibility and options for sustainable drainage systems at a large site in Rhoose; the case study can be found here.

We implement soakaway and infiltration testing for a range of private and public clients on a weekly basis, so please get in touch to see how we can help.

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