The Risk of Avoiding SuDS in Development
A recent appeal decision highlights the importance of following the SuDS hierarchy and providing evidence-based drainage strategies to avoid planning refusal.
Additional data requests, such as a CCTV survey or infiltration testing, can seem like unnecessary extra costs, especially when you have just appointed a Surface Water Drainage Engineer who is now requesting more information to support their work. But consider the alternative. For example, a Thames Water Asset Plan costs as little as £68 + VAT, and a CCTV survey for a single dwelling typically ranges from £400 to £800. What if not having this information led to a planning refusal? The resulting delays in sourcing the missing data—or, worse, the need for a full resubmission—could cost significantly more, particularly given the recent increase in planning application fees. The reality is that this risk is becoming increasingly common, as highlighted in a recent appeal decision where limited evidence and a failure to follow the SuDS hierarchy resulted in refusal.
Appeal Decision Highlights Risks of Avoiding SuDS
A recent appeal decision has highlighted the importance of applying sustainable drainage systems (SuDS) in accordance with both local and national planning policies. While SuDS are not currently mandatory across England, many local planning authorities require them through adopted policy. This case demonstrates that developers cannot rely solely on their legal right to connect to the public sewer without first showing that SuDS have been fully considered. Crucially, the SuDS hierarchy must be followed and clearly evidenced to justify how a site will effectively manage and mitigate surface water.
In this case, Local Plan Policy W DM3 — Sustainable Urban Drainage Systems — specifically required adherence to the hierarchy of preferred drainage solutions, as set out in Approved Document H of the Building Regulations and the SuDS Manual (CIRIA C753).
SuDS Policy & National Standards
Although there is no statutory requirement for SuDS in England, the government has published the National Standards for Sustainable Drainage Systems to guide their design and application. These sit alongside the National Planning Policy Framework, which encourages the use of SuDS in new developments. By contrast, Wales has implemented Schedule 3 of the Flood and Water Management Act 2010, making SuDS mandatory for most new developments. The Independent Water Commission recently recommended that Schedule 3 be implemented across England to bring consistency and ensure surface water is managed more sustainably.
Understanding the SuDS Hierarchy
The SuDS hierarchy is a step-by-step approach that prioritises draining surface water as close to its source as possible. This approach reduces flood risk, improves water quality and supports biodiversity. Planning policies increasingly require developers to demonstrate that they have followed this hierarchy when preparing drainage strategies.
The SuDS hierarchy in Arun District Council states:
“The following destinations must be considered for surface runoff in order of preference:
- Discharge into the ground (infiltration).
- Controlled discharge to a surface water body.
- Controlled discharge to a surface water sewer.
Notes:
- surface water must not be discharged into the foul sewer system
- infiltration structures include soakaways, basins, swales and permeable paving
- open SuDS features are encouraged
- structures that span individual property boundaries are discouraged
- discharge to surface water bodies and surface water sewers must be restricted to an agreed rate”
The National Standards for Sustainable Drainage Systems (SuDS) 2025 hierarchy is similarly:
- Collected for non-potable use e.g. rainwater harvesting (e.g. toilet flushing, irrigation)
- Infiltrated to the ground.
- Discharged to an above-ground surface water body.
- Discharged to a surface water sewer or another piped drainage system.
- Discharged to a combined sewer.
Developers should provide evidence to justify using lower-priority and less sustainable discharge locations. As experts we should only progress to the next sequential option of the hierarchy once we have discounted the current step on an evidential basis.
Case Study: Planning Refusal Without SuDS
In this particular appeal, the developer proposed to discharge surface water into a foul-only public sewer. They argued that they had a legal right to connect under the Water Industry Act 1991 and that no reasonable alternatives were available. Arun District Council, however, rejected this argument. The Council stated that the SuDS hierarchy had not been followed, and that no evidence had been provided to show that other, more sustainable options had been explored.
The appeal was dismissed following an inquiry, with the Planning Inspector concluding that the drainage strategy did not comply with local policy. The decision noted that the appellant had not adequately demonstrated that the SuDS hierarchy had been considered, nor that alternatives to the sewer connection had been properly investigated.
What This Means for Developers
This decision is a clear reminder that drainage strategy must be aligned with planning policy. Where local authorities require SuDS, developers must present clear evidence that they have followed the SuDS hierarchy and provide justification where alternatives are proposed. As support grows for the adoption of Schedule 3 in England, sustainable drainage is likely to become more than just good practice; it may soon be a statutory requirement.
What does this mean in practice?
The SuDS hierarchy is built on an evidential approach. While gathering additional data may initially seem like an extra cost, it is essential for informing surface water drainage strategies and increasingly critical for validating planning applications. Typical supporting information can include:
- Infiltration and percolation testing
- Winter groundwater monitoring
- Asset plans and capacity checks
- CCTV surveys
- Topographic surveys
- Pre- and post-development level data
Access to this information enables the selection of the most appropriate methods for managing surface water runoff post-development, in line with CIRIA C753, the NPPF, and local planning policies.
Although it may be tempting to limit upfront expenditure, the lack of robust evidence often leads to planning refusals — as seen both at initial application stage and on appeal. This focus has intensified following the Cunliffe Report, which highlights the need for the water industry to strengthen efforts to reduce pressure on already stressed water infrastructure and the wider environment.
By prioritising sustainable drainage measures, we can not only ensure compliance with policy but also help to reduce the frequency of combined sewer overflows, delivering wider environmental benefits.