Sustainable Drainage Systems (SuDS) Design: A Complete Guide
In the UK, almost all new developments must incorporate SuDS design. Learn what types are available and how they can benefit the wider area.
What are SuDs?
Sustainable drainage systems (SuDS) are designed to manage surface water and control flooding by working with the local biodiversity and the land’s natural characteristics, rather than against them. They mimic natural flood management systems and manage rain where it falls to deliver long-term solutions to water control.
Adopting a more environmentally friendly approach to flood risk management has a wide range of benefits for both local residents and the wider ecological area. An effective SuDS can improve water and air quality, reduce carbon emissions, and improve water availability.
What is a Sustainable Drainage System?
Sustainable drainage systems are unique, custom-designed drainage strategies. While they used to be a “nice-to-have”, under the National Planning Policy Framework (2025), they’re now required for planning permission approval on both commercial and domestic projects.
To deliver long-term, sustainable drainage, SuDS must replicate natural processes local to the area that capture, store, and transport rainwater. Rather than opting for traditional underground pipes, SuDS use natural methods such as permeable paths, vegetation, and drainage basins.
How to Develop a SuDS Strategy
Most developments will need several SuDS working concurrently to provide long-lasting flood control. Each strategy is developed bespoke to the area, as different locations will pose unique challenges and requirements.
Experienced civil engineers will assess your land’s specific drainage characteristics and the potential impact of any strategies downstream. They’ll use this to identify the most effective sustainable drainage systems, and after completing a risk assessment in line with the UK Government’s requirements, they can begin installation.
Sustainable systems do not have to be installed at the beginning of a project, and many strategies are easily retrofitted. Developments built prior to SuDS becoming mandatory for planning permission approval can adopt a range of techniques to manage flood risk at any time.
Types of Sustainable Drainage Systems
Sustainable drainage systems manage water where it enters the system, aiming to reduce runoff and store it closer to its source. This lowers the risk of flooding downstream. Engineers use a combination of several drainage methods, including storage, filtration, and wetlands.
Infiltration
Infiltration drainage systems slow the water’s journey downstream by allowing it to infiltrate and filter through the subsoil layer. There are several different methods for achieving this:
- Soakaways can temporarily store runoff from single properties or entire developments in a rubble-filled pit below the surface before it filters through into the surrounding soil.
- Infiltration trenches work similarly to soakaways, except their pits are filled with gravel or crushed stone. They’re depressed into the ground to encourage water infiltration. Plants and trees, typically with deep root systems for better drainage, can be added.
- Bioretention areas/rain gardens are vegetated plots with sand and gravel underneath the soil that store water and provide advanced filtration, removing metals and bacteria.
- Permeable pathways provide routes for water to penetrate through the ground and enter the subsoil, avoiding excessive runoff into watercourses.
Before an infiltration system is established, engineers must consult the Environment Agency’s Groundwater Source Protection Zones (SPZs). This ensures there’s no risk to groundwater quality, which constitutes a third of the UK’s drinking water
Detention and Retention
Detention and Retention SuDS are designed to provide flood relief by either storing groundwater or slowing its path downstream. They’re most commonly ponds or underground storage areas:
- Detention basins are large, flat areas of grass that temporarily store groundwater after heavy rainfall. Their size can vary significantly depending on the needs of the area.
- Retention ponds are permanent storage basins that are often specially engineered to slow the release of water after heavy rainfall. They can support local biodiversity and serve as a recreational area for the local community.
Conveyance
Effective SuDS require conveyance methods, which facilitate the transfer of surface water runoff across the area and between systems. Failing to control conveyance can lead to an elevated and unpredictable flood risk. It’s primarily controlled through channels of varying size:
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- Channels and rills are shallow, linear, surface water routes that collect and provide a downstream route. Rills are smaller and usually hard-lined, while channels move greater quantities of water towards treatment centres.
- Swales are smaller, broader vegetated channels that provide temporary flood relief by collecting rainfall. They also provide filtration to remove impurities from the soil.
Green Roofs
A green or living roof has plants growing on it that store water and can retain up to 90% of runoff during the summer months. They also store carbon and provide noise and sound insulation.
Wetland Creation and Restoration
Wetlands are excellent at treating polluted runoff and provide a biodiverse environment. They are shallow areas that are either seasonally or permanently saturated and have dense vegetation.
Wetlands slow the flow of water significantly, allowing enough time for sediment to drop out of suspension. The vegetation filters the water and removes heavy metals, nutrients, and fine sediments. The water gradually moves into local watercourses.
Some plant and animal species have evolved to thrive in a wetland’s unique environment and can’t survive elsewhere. Up to 25% of all wetland species are threatened with extinction, and creating new areas of wetland while preserving pre-existing ones can help endangered species thrive.
Rainwater Collection
Best suited to smaller developments and residential properties, water butts can harvest rainwater to control stormwater runoff. The water can be recycled to conserve groundwater and reduce energy use from treatment plants.
Sustainable Drainage Systems vs Traditional Flood Management
Older, traditional flood management systems relied heavily on underground pipes to move surface water away from properties and built-up urban areas. However, hastily moving water away from where it falls can overwhelm sewage and treatment plants and worsen downstream flooding.
In contrast, SuDS manage rainfall at the point where it enters the drainage system. They slow the flow of water, allowing for local absorption and filtration, to lower flood risk and remove pollutants.
| Features | SuDS | Traditional Flood Management |
| Infrastructure involved | Bioretention strips, retention ponds, permeable pathways, detention basins, channels, green roofs, and wetlands. | Extensive underground pipes, tunnels, and sewers. |
|---|---|---|
| Cost of installation | Up to 30% cheaper than traditional flood management. | More expensive than SuDS alternatives. |
| Maintenance required |
Low to moderate maintenance. Grass cutting and litter picking are required monthly, and erosion repairs and silt removal are needed as necessary. |
Medium to high maintenance.
Monthly removal of debris and litter is essential, and large-scale repair works are required on concrete and channel beds every 5-10 years. |
| Longevity | Designed to last for the lifetime of the development, but could remain functional for generations. | Approximately 50 years, provided they receive regular maintenance. |
| Climate resilience | Vegetation in SuDS, such as wetlands, bioretention strips, and permeable pathways, stores carbon, regulates temperatures, and reduces air pollution. | No, they can become overwhelmed during extreme weather events. |
| Supports biodiversity | Many SuDS methods provide habitat for a range of species. | No. |
| Community benefits | Flood management, improved local spaces, better air quality, and temperature control. | Flood control. |
Sustainable Drainage Design From The Home Engineers
Our team of experienced civil engineers have created sustainable drainage systems for a variety of development types, designed to reduce flood risk and maintenance costs, while supporting local communities and biodiversity.
To get started on your sustainable drainage system, get in touch with our team today.
Sustainable Drainage Systems Design FAQs
Yes, a sustainable drainage system is required for all new developments. Only under exceptional circumstances where a SuDS would not be appropriate are they not essential, and this must be proven with extensive evidence.
Yes, many sustainable drainage systems can be retrofitted into older developments that are reliant on traditional flood control.
As each sustainable drainage system is bespoke and carefully aligned with the natural characteristics at the location, the cost can vary significantly from site to site. Key factors affecting price include site size, flood risk, and the number of systems required.
Once we have details regarding your development and needs, we can provide you with a quote.
Our team of experienced civil engineers will assess your development requirements and the local area to develop an effective, sustainable drainage strategy. Once we’ve completed our assessment, we’ll report the findings to you and develop a tailored drainage system.
It is often recommended that engineers designing SuDS consider landscaping. This is because the most effective SuDS are complementary to its natural surroundings. For instance, landscaping can help emphasise basins and create low flow channels to help direct water and manage sedimentation.