UK – Finding a Place for Sustainable Drainage System (SuDS) in Flood Protection

The Chartered Institution of Water and Environmental Management (CIWEM) recently published a report containing its findings on the barriers to the implementation of Sustainable Drainage System (SuDS) in England, following the adoption of the Housing and Planning Act 2016 (pdf).

With the new Act underpinning the government’s aim of building one million new homes by 2020, CIWEM notes that one in six existing homes is in an area that is at risk of flooding, and that surface water flooding is an increasing problem which the incorporation of SuDS can help to alleviate. The Act requires at Section 171 that the Secretary of State carry out a review of “planning legislation, government planning policy and local planning policies concerning sustainable drainage in relation to development of land in England”, and CIWEM considers that the findings of the survey represent “a real opportunity for improved practice, which strengthens policy and standards.”

The “Big SuDS Survey”

The report, A Place for SuDS (pdf), analyses the responses contained in CIWEM’s “Big SuDS Survey” undertaken in July 2016 of 539 respondents in the private and public sectors in England. The survey was supported by professional organisations and bodies including the RTPI, ICE, RIBA, IES, WWT and the Landscape Institute (see also the FloodList article here).

Analysis of the responses indicated that the main obstacles to wide implementation of high quality SuDS are “political and institutional rather than technical or financial”. The main findings are summarized in the following points:

  1. At the majority of sites, the costs and particularly the benefits of implementing SuDS, are not being assessed.
  2. Physical site constraints are cited frequently as reasons to ‘opt-out’ of delivering SuDS in new housing and commercial developments, when the range of options available means this is commonly unjustified.
  3. In many areas planning authorities do not have the capacity to judge the merits of applications properly, leading to more opt-outs than necessary on the grounds of price and practicality as many go unchallenged.
  4. Where SuDS have been delivered, they often miss opportunities to provide multiple benefits as they follow the very narrow non-statutory standards that exist presently.
  5. The adoption and future maintenance of SuDS are the greatest barriers to be resolved.

Summary of Responses

The survey found that almost 75% of respondents don’t assess the costs and benefits of SuDS schemes, however Defra has elsewhere found that construction and maintenance costs of SuDS are on average similar to, and often cheaper, than those for conventional drainage systems. And while the survey found that physical constraints are often cited as a reason for “opt-out” of SuDS provision, the authors of the report note there are numerous alternative SuDS methods that require very little space. Furthermore, they note that there is limited evidence that the need to consider SuDS causes delays in the planning evaluation process, but that, where delays occur, “they are often the result of uncertainty over the on-going maintenance of the systems, rather than construction of the SuDS themselves”.

15% of respondents indicated that health and safety factors were a reason why SuDS might not be considered acceptable. The writers of the report, however, are of the opinion that appropriate designs can be used that remove any danger to surrounding residents. They note that SuDS projects have been safely and successfully implemented at schools and are, in addition, a useful educational tool.

Policy Constraints

The report contains an incisive analysis of planning policy and practice as it relates to SuDS evaluation and implementation; noting that over 70% of respondents were of the opinion that current planning policies do not sufficiently encourage implementation of SuDS.

Four policy and institutional barriers were identified in the survey as needing to be addressed: weak planning policy, lack of sufficient resources at local authority level to drive and enforce quality SuDS implementation, a lack of clarity around SuDS ‘adoption’, and weak standards leading to poor quality schemes. These barriers were considered by CIWEM as being “the main reason for limited uptake of high quality SuDS.”

The policy of restricting SuDS requirements to new developments equivalent to 10 residential units or more misses a large segment of contributors to stormwater runoff – according to the report this segment represents 90% of planning applications.

The absence of a policy requiring retrofitting of SuDS where appropriate is another missed opportunity to address contributing factors to surface water flooding.

Permitting the continued right to connect surface run-off water directly to existing sewer systems is a growing problem, especially while water and sewerage companies are not statutory consultees in the planning process.

Lack of skills and resources at local planning (LPA) and lead local flood authority (LLFA) level is an urgent problem that needs to be addressed – 75% of respondents were of the opinion that these bodies lacked capacity, and almost 40% felt that stricter planning enforcement would improve the uptake of SuDS.

Clarification of responsibility for implementation and ongoing maintenance was highlighted as the top priority for government review. SuDS often, by their very nature, cross the boundary between private and public land with private developers and owners reluctant to take on the long term maintenance burden of SuDS on their land. On the other hand, the local authority is often under budgetary constraints and is not keen to take on additional responsibilities, while being unable to ‘ring-fence’ contributions for SuDS maintenance from private owners. As such there is often incentive for both parties to settle for an ‘opt-out’ situation.


The report concludes with the following proposals:

Discharge of surface water to the sewer system should be conditional on the inclusion first of high-quality SuDS in new developments.

  1. A clear decision must be taken with regard to the adoption and allocation of maintenance responsibilities for SuDS. This should have a clear and established mechanism for raising funds to ensure the continued effective maintenance and eventual replacement of all SuDS they adopt.
  2. New standards are developed aimed at optimising opportunity to achieve amenity, biodiversity and water quality benefits as well as flood risk reduction. These should reflect the needs of the adopting authority so that they can set out an approval process and adopt with confidence.
  3. The Government should undertake a follow up review of the barriers to retrofitting SuDS in existing developments and make proposals on how retrofitting might be incentivised.

The report also contains informative case studies, including outlines of SuDS policy in Wales, Scotland and Northern Ireland.

The report contains well-informed analysis of, and comment on, the status of SuDS implementation in England and will provide valuable input to the review process required in terms of the Housing and Planning Act, 2016.

Bioretention / bioswale in median of Grange Avenue in Greendale, Wisconsin, July 2010. Photo: Aaron Volkening, CC BY 2.0