Sustainable Drainage Systems (SuDS) are drainage features designed to manage rainwater in a more natural way. Instead of sending water directly into underground pipes and sewers, SuDS help slow, store, filter and absorb rainfall close to where it lands. Common examples include rain gardens, tree pits, permeable paving and green roofs. They: Slow down surface water runoff Reduce pressure on the sewer network Lower the risk of surface water flooding Improve water quality, biodiversity, and urban amenity By reducing reliance on traditional drainage systems and stormwater overflows, SuDS offer a more sustainable solution for managing water.

Why are SuDS needed in Westminster?

Surface water flooding is one of the most common forms of flooding in the UK and is the most likely cause of flooding in Westminster. It occurs when heavy rainfall overwhelms drains and sewers, causing water to collect on streets, pavements and other hard surfaces before potentially entering homes, businesses and public spaces. Unlike river flooding, surface water flooding can occur almost anywhere and is not limited to areas close to rivers or watercourses. In densely built-up areas such as Westminster, where much of the land is covered by buildings, roads and paving, there is less opportunity for rainwater to soak naturally into the ground. Across two major flood events in July 2021, over 400 properties were affected by surface water and/or sewer flooding.

What type of SuDS are used across Westminster?

At present, SuDS used across Westminster include: Rain gardens Permeable paving Tree pits Planters Green walls Green or blue roofs SuDS that incorporate planting and other green features can create habitats for plants, pollinators and wildlife, helping to support biodiversity across Westminster. They can also help cool urban areas by providing shade and increasing evaporation from vegetation, reducing the urban heat island effect and making streets and public spaces more comfortable during hot weather. Although green roofs, blue roofs and green walls can form part of a sustainable drainage strategy, they are not a primary focus of the SuDS Masterplan. These features are generally more commonly delivered through new developments and major redevelopment projects, whereas the Masterplan focuses on retrofit opportunities within Westminster's streets and public spaces.

Will SuDS reduce flooding on my street and how will you measure it?

SuDS capture and slow rainwater before it reaches the sewer. A single feature won’t prevent flooding on its own, but the effect is cumulative: the more SuDS are delivered across Westminster, the more rainwater is held back, and the lower the risk of flooding becomes. We will monitor how well SuDS perform using probes that measure the amount of rainwater stored. This will show us how they work and help us improve future schemes.

How have Westminster City Council decided where to deliver SuDS?

Across Westminster, the delivery of SuDS is being strategically planned and implemented on a catchment-based approach, helping to manage rainwater across entire areas rather than treating individual locations in isolation. Like river catchments, surface water catchments are areas where rainfall naturally flows towards key drainage points. Westminster has been split into 14 catchments, which have been prioritised based on factors such as historic flooding, maximum attenuation volume, environmental impact and social value benefit.

What can I influence in Westminster’s SuDS delivery?

As SuDS proposals are developed across Westminster, we will ask the community for feedback to help shape the designs. This engagement will gather local insight to ensure the proposals work effectively, while also seeking views on their appearance and design so they enhance the local area. Careful assessments are being undertaken to identify the SuDS interventions that are technically suitable for each area. The engagement activities are designed to gather feedback only on the aspects of the designs that the community can genuinely influence.

Is it possible to suggest locations for SuDS interventions?

Yes – residents can suggest possible locations for SuDS. Due the technical constraints of installing SuDS, proposed locations would have to be assessed through the same process as locations identified through the masterplan.

How will SuDS work alongside existing drains and sewers?

SuDS work with the existing drainage network rather than replacing it. They capture rainwater where it falls, hold it and release it more slowly into the existing drains. This reduces the amount of water entering the combined sewer at once, particularly during heavy rain. The drains and sewer will keep doing their job. SuDS simply take some of the pressure off them.

Will the delivery of SuDS cause significant construction disturbance?

During SuDS delivery, Westminster City Council will work closely with affected communities to provide clear information about scheduled construction works and minimise disruption. Works will follow core hours of 08:00–18:00 on weekdays and 08:00–13:00 on Saturdays. While construction disruption cannot be avoided entirely, advance notice and information about the type of works planned will help communities understand what to expect and plan accordingly.

Will SuDS affect my property value?

We are not aware of any evidence that SuDS reduce property values. Features like rain gardens and planted areas can make streets greener and more attractive and reducing flood risk can be a positive for local properties.

Will I lose parking spaces or pavement width?

SuDS features need space, so in some locations they may affect parking bays or pavement space. We would only replace parking bays in areas where occupancy is low and where the SuDS feature is high value in terms of the catchment size and volume of rainwater attenuated. We would consult on any proposed changes to parking before they go ahead. Pavements will be kept in line with accessibility standards so people with mobility needs, including wheelchairs and pushchair users, can still get around safely.

Will SuDS work in a drought?

Yes. SuDS are designed to cope with periods of both very wet and very dry weather. During prolonged dry spells, rain gardens may appear drier, but they remain ready to capture and manage rainwater when rainfall returns. Plants are carefully selected to tolerate a range of wet and dry conditions, helping them remain resilient as weather conditions change. The proposed rain gardens will also include an additional aggregate storage layer, which can retain moisture and allow plants to draw on it during drier periods. As part of the ongoing maintenance regime, the condition of the planting will be monitored and, where necessary, additional watering may be carried out during prolonged dry spells to help keep plants healthy.

What happens if SuDS fail or get blocked and who do I report problems to?

SuDS are maintained by Westminster City Council’s highways department through its nominated contractor. They are inspected regularly and maintenance includes clearing litter and debris from the inlets. If you notice a SuDS feature that is blocked, damaged or not draining properly, please report it via the Report It function on our website.

Raingardens in Westbourne Green Canalside

Project

Frequently Asked Questions

Here we answer some of the Frequently Asked Questions about Sustainable Drainage Systems (SuDS) and our SuDS programme.