What are sustainable urban drainage systems?

Sustainable urban drainage systems (SuDS) are a sequence of water management practices and facilities designed to drain surface water in a manner that will provide a more sustainable approach than what has been the conventional practice of routing run-off through a pipe to a watercourse or sewer. Examples of elements which can be incorporated into SuDS are permeable paving or road surfaces, soakaways, green roofs, swales (depressions filled with aggregates allowing water to drain away slowly), ponds.


Following some of the worst floods in living memory in 2007 the Government commissioned Sir Michael Pitt to report on how the country could increase its resilience.

A key recommendation was the use of eco-friendly SuDS and this was included in schedule 3 of the Flood and Water Management Act, passed in April 2010.  This provided that SuDS would be compulsory in all new developments from April 2014.  The Act also proposed that SuDS be approved, adopted and maintained by SuDS approval bodies (SABs). These would be the responsibility of flooding and drainage authorities (county or unitary councils), with a consent process separate to planning.

In April 2014, the Government announced full implementation of schedule 3 would have to wait until all drainage authorities had set up a SAB. But in summer 2014, the Government published a second consultation which signalled a change of direction.  In the consultation "Delivering Sustainable Drainage Systems (September 2014)", DEFRA and DCLG also announced that the responsibility for approving and maintaining SuDS would be transferred to the planning system and local planning authorities (LPAs).  This was followed on 18 December 2014 with the Government issuing a Written Statement (HCWS161) which confirmed that responsibility for SuDS would instead be introduced through modifications to existing planning guidance.

SuDs – a material planning consideration

When considering a planning application, the LPA must determine the application in accordance with the Local Plan, unless material planning considerations indicate otherwise. The evidence supporting the Strategic Flood Risk Assessment can be used by the LPA to inform their judgement both on the appropriateness of the proposed development and on the suitability of any proposed drainage system.

The National Planning Policy Framework (NPPF) highlights that inappropriate development in areas at risk of flooding should be avoided by directing development away from areas at highest risk, but where development is necessary, making it safe without increasing flood risk elsewhere (paragraph 100).

There is a clear policy requirement in the NPPF for SuDS to be considered (paragraph 103), but note that the NPPF requires SuDS to be prioritised for new developments only in areas at risk of flooding.

The Written Statement 2014 made it clear that SuDS are a material consideration in the determination of all planning applications for major developments from 6 April 2015.  The Written Statement confirms that in considering planning applications, LPAs should consult the relevant Lead Local Flood Authority (county councils and unitary authorities) (LLFAs) on the management of surface water; satisfy themselves that the proposed minimum standards of operation are appropriate and ensure through the use of planning conditions or planning obligations that there are clear arrangements in place for ongoing maintenance over the lifetime of the development.

The Planning Practice Guidance (PPG) was updated on 23 March 2015 and gives effect to the Government's intention to make the approval of SuDS, as well as their technical fitness for particular developments, the responsibility of LPAs.  The updated PPG imports several provisions from the 'Non-statutory technical standards for sustainable drainage systems' published in March 2015 by Defra (the Technical Standards).

Alongside the changes to guidance the Town and County Planning (Development Management Procedure) (England) Order was amended to make LLFAs statutory consultees in the planning process for major development proposals which have surface water implications starting from 15 April 2015.

A 'major' planning application is defined in Part 1(2) of The Town and Country Planning (Development Management Procedure) (England) Order 2015:

  • residential development: 10 dwellings or more or residential development with a site area of 0.5 hectares or more where the number of dwellings is not yet known
  • non-residential development: provision of a building or buildings where the total floor space to be created is 1000 square metres or more or where the floor area is not yet known, a site area of 1 hectare or more.

For 'major' developments, the LPA's expectation will consequently be that SuDS for the management of run-off are put in place, unless demonstrated to be inappropriate.

In considering planning applications for 'major' development, the LPAs will need to consult the relevant LLFA on the management of surface water; satisfy itself that the proposed minimum standards of operation are appropriate and ensure through the use of planning conditions or planning obligations that there are clear arrangements in place for ongoing maintenance over the lifetime of the development. 

Minor development will be all those which fall below the thresholds set out for major developments. Respondents to the September 2014 consultation (referred to above) raised concerns about the potential cumulative impact of minor developments on flood risk.  The Secretary of State for Defra wrote specifically on this issue to the Chairman of the Climate Change Committee Adaption Sub-Committee (letter dated 18 December 2014).  This letter notes that the existing requirement under the NPPF to prioritise the use of SuDS in areas at risk of flooding remains in place for minor development.  The letter confirms that LPAs "would continue to ensure that flood risk is not increased by any new development and that SuDS are considered for all new developments regardless of size." As already noted above, the NPPF only requires SuDS to be prioritised in areas at risk of flooding.  The letter confirms that the Government will keep the effectiveness of the approach under review. 

What does this mean for developers/ applicants?

December’s Written Statement sets out new policy on SuDS which should be read alongside the NPPF.  This means that SuDS are a material consideration for all major development, irrespective of location, wherever SuDS would be appropriate.

There will therefore be an expectation that robust and sustainable arrangements for the maintenance of SuDS will form part of new major development proposals.  Applicants will need to submit sufficient information, both in respect to the design of systems and their future maintenance to enable the LLFA and therefore the LPA to discharge its duties.

The NPPF already provides that in areas which have been identified as being at risk of flooding a site-specific flood risk assessment is required for proposals for major development in Flood Zone 1.  All proposals for new development (including minor development and change of use) in Flood Zones 2 and 3, or in an area within Flood Zone 1 which has critical drainage problems (as notified to the LPA by the Environment Agency); and where proposed development or a change of use to a more vulnerable class may be subject to other sources of flooding, require a site-specific flood risk assessment (paragraph 103 NPPF).  The flood risk assessment should, amongst other things, help demonstrate that priority is being given to SuDS in areas at risk of flooding.

From 6 April 2015, on all applications for major development (whether in an area identified as at risk of flooding or not), LPAs will be looking to applicants to provide a detailed SuDS design strategy with full applications (to include the detailed design, management and maintenance of surface water management systems including SuDS).  For outline applications LPAs will be looking to applicants to provide a concept SuDS plan and preliminary SuDS design strategy. 

On minor applications not in areas at risk of flooding, LPAs will be looking for evidence that sustainable drainage (SuDS) have been considered. 

In considering a development that includes a sustainable drainage system an LPA will 'want to be satisfied that the proposed minimum standards of operation are appropriate' (PPG paragraph 81), and that 'there are clear arrangements in place for ongoing maintenance' when considering a development which will include a SuDS.

The revised PPG also incorporates the "drainage hierarchy" for surface water drainage from the Technical Standards, although adherence to the hierarchy has been made less strictly prescriptive.  The changes clarify the "costs tests" in relation to following the Technical Standards, which should give developers more flexibility when deciding how strictly to follow them.  If following the Standards would be more expensive than following building regulations, then this is unlikely to count as 'reasonably practicable' for the purpose of the PPG: so long as, by not following them, the risk of flooding is not increased elsewhere. 

Maintenance and adoption

If LPAs are responsible for delivery of SuDS, they will need to make decisions which are technical in nature, though many may not be equipped for this.  The updated guidance therefore features an increased emphasis on consultation with LLFAs to bridge this perceived gap. 

While LPAs may be able to manage the technical review of proposed SuDS by drawing on external expertise, the updated PPG does little to address the most difficult issue inhibiting the development of SuDS, that of long-term maintenance.  

The PPG requires there to be "clear arrangements in place" (paragraph 81) for ongoing maintenance, and for maintenance to be 'accounted for' in the SuD's design (paragraph 85).   

Our thoughts

The revised PPG is not prescriptive and leaves it open to developers and LPAs to implement a solution to cover the ongoing maintenance of any SuDS.  Developers will therefore have a number of options: 

  1. to enter into an arrangement with a third party for long-term maintenance
  2. to design SuDS so they may be adopted by the local highway authority (only available where the SuDS is adjacent to a highway), or
  3. arrange for the adoption of the SuDS by a water or sewerage utility. 

Many LPAs have developed and are developing supplementary planning guidance relating to SuDS.  For example Oxford City Council's highway authority has played an active role in adopting SuDS adjacent to highways.  In parts of Bristol and in conjunction with Sustrans, 'rain gardens' which are SuDS set in the public highway, are being developed (also potentially doubling as traffic-calming measures).   

However, for major developments it will not always be possible to provide SuDS using only highway land.  This may therefore lead to an increase in obligations required under S106 agreements to provide a period of funding for the maintenance of new SuDS, or arrangements for SuDS to be adopted by utilities where possible. 

Agreements for the adoption of SuDS which will 'communicate with a public sewer' (a solution available within the drainage hierarchy) remain available under S104 of the Water Industry Act 1991.  If any SuDS works are to be adopted under a S104 agreement, they will have to comply with the CESWI Sewers for Adoption standards.  Designing systems which comply with sewer adoption standards and  the Technical Standards, and at the same time demonstrating that a "clear agreement" is in place for the long-term maintenance of the SuDS, is likely to be achallenge for any developer.

Indeed under the existing system, water and sewer utilities have found the adoption of SuDS difficult, as the Technical Standards provided by the Government to date do not result in developers consistently bringing SuDS to an appropriate standard for adoption.

If a utility is amenable to adopting a SuDS, this may be an attractive option for a developer, but achieving the appropriate standards will have cost implications and will also require engagement with the utility at an early stage.  This should be done before commitments to the SuDS scale or design have been made.