Raingardens - making space for new SuDS policy and climate resilient design

There has been a substantial increase in Lead Local Flood Authorities’ (LLFAs) and SuDS Approval Bodies’ (SABs) requirements for the inclusion of sustainable drainage systems (SuDS) on development schemes. This shift follows the publication of national standards for sustainable drainage Systems, in mid-2025. The new standards reflect a change in how surface water is managed in the built environment and places a greater responsibility on developers and designers to ensure that SuDS are no longer viewed as “an addition,” but integrated as core infrastructure. They also reinforce the requirement to meet the four pillars of SuDS design – water quantity, water quality, amenity and biodiversity.  

Similarly in 2025, the Environment Agency (EA) published new national risk information for flooding and coastal erosion. This includes revised National Flood Risk Assessment (NaFRA) datasets that account for future climate change scenarios, placing increased importance on delivering SuDS-based drainage solutions.

What are raingardens?

These recent national updates, and policy implementation, means there is a greater need for SuDS to be incorporated at the conceptual design stage. This ensures that there is sufficient space for their effective use. One highly effective SuDS solution is raingardens. Raingardens are gaining popularity as a cost effective option, particularly on brownfield, constrained, urban sites.

Raingardens are landscaped depressions that collect, store, and reduce surface water runoff rates and volumes. They also provide interception treatment and pollution mitigation using engineered soils, permeable subbases, and vegetation.  Overland runoff directed into raingardens is temporarily held at the surface before filtering through the vegetation, underlying soil, and storage layers. Depending on site conditions, the filtered water is then either collected by an underdrain system or discharged via infiltration. A small proportion of runoff is also lost through evapotranspiration.

Why raingardens work on constrained urban sites

The question then becomes: why are we not seeing more rain gardens being implemented on sites?  It is worth noting that large multi-unit and greenfield sites benefit from the ability to integrate a full range of blue and green SuDS infrastructure such as swales, ponds, detention basins and other engineered large scale bioretention systems. However, smaller single-unit urban sites, and brownfield sites don’t usually benefit from this due to the numerous competing constraints on space, such as utilities, parking space and service vehicles, pedestrian routes, land values, and the requirement to maximise development returns. As a result, options for delivering SuDS that provide source control benefits are often limited.

Space constraints can prevent the use of swales or above ground storage, while roof level blue and green infrastructure is often value engineered out of schemes due to cost, structural implications, architectural preferences, or maintenance considerations. In addition, many local authorities are increasingly reluctant to adopt permeable paving solutions because of concerns regarding maintenance requirements and the risk of system failure.

As a result, conventional below ground drainage solutions, such as cellular storage tanks, are frequently relied upon. Although these remain accepted, ‘tried and tested’ options that effectively deliver peak flow and volume control, they are associated with higher upfront embodied carbon due to carbon intensive construction methods. However, with the introduction of the new national SuDS standards, local authorities are likely to continue to challenge schemes that do not incorporate source control SuDS measures for all areas of positive surface water runoff.

In short, raingardens provide a simple, cost effective, and low maintenance SuDS solutions (CIRIA, C753). They allow surface water management to be integrated with soft landscaping and deliver associated Biodiversity Net Gain (BNG) benefits.  They are also visually attractive features that enhance amenity, support community wellbeing, improve biodiversity, and uplift the overall quality of the public realm.  

Key considerations for a raingarden

Despite their many benefits, raingardens are still not readily included at the conceptual design stage.  A key barrier is perception rather than performance. Because raingardens are still relatively unfamiliar, they are sometimes assumed to be costly or high‑risk.  

Greater early engagement is therefore needed to work with the whole design team, including architects and landscape architects, to ensure raingardens are embedded into masterplans from the outset. This includes advising on soil and planting specifications, producing detailed construction drawings that align with best practice and manufacturers’ guidance, and educating clients and the public about how these systems function. It is important to dispel the perception that a raingarden containing water has “flooded” or failed. Temporary surface ponding is an intended part of the design.

Raingardens do require regular maintenance to ensure they continue operating to design standards. The most common cause of failure is surface clogging, which is usually easy to identify. If surface layers clog or underlying drainage components fail, this can lead to reduced infiltration, persistent ponding, and poorer water quality as flows bypass the filtration media.  When designed and maintained correctly, raingardens perform reliably throughout their lifespan and are no more complex to maintain than standard planted areas.

Why raingardens deserve a place at the start of design

Policy changes and national guidance are accelerating the need for genuinely integrated SuDS solutions that deliver source control, resilience, and wider environmental benefits. Raingardens represent a practical and adaptable opportunity, particularly on constrained urban and brownfield sites, to meet these requirements while enhancing amenity, biodiversity, and placemaking.  

When considered early in the design process and supported by appropriate technical input and maintenance planning, raingardens can move SuDS from a perceived constraint to a value adding component of development. As expectations continue to evolve, embedding raingardens at the heart of scheme design will be key to delivering compliant, low carbon, and future ready drainage solutions.