Sustainable Drainage Systems (SuDS)

Traditional engineering solutions are gradually being replaced or integrated with sustainable solutions – often centred around the blue-green infrastructure (BGI) approach. New methods are inevitable not least due to greater population densities and expanding impervious surfaces in urban areas which, combined with extreme climate events, intensify pressure on water drainage systems

From traditional to transformational

Out with the old…

The negative impacts of conventional drainage – limited capacity causing flooding, watercourse pollution and loss of natural infiltration – is well recognised. Traditional pipe drainage collects and conveys water away from where it rains, as quickly as possible, contributing to increased risk of flooding, likelihood of contaminated water and the loss of our relationship with water and the benefits it can bring.

1. Fewer green areas and parks
2. Hard landscape areas
3. Additional treatment volumes
4. Lack of capacity
5. Pollution of Receiving Waters
6. Reduced groundwater recharge
7. Drought and wildlife stress
8. Land erosion

In with the new…

Implementing SuDS on the other hand, is a way of managing rainfall that mimics the drainage processes found in nature. In turn, it reduces the impact of new and existing developments with respect to water in both rural and urban areas by replicating natural systems.

• Improved air and water quality
• Better community health and wellbeing
• Improved habitats for wildlife
• Flood prevention and reduction
• Natural groundwater recharge

How to achieve the four principles:

1. Storing runoff, i.e., in ponds, basins, bioretention gardens and releasing it slowly at controlled, usually greenfield, rates
2. Harvesting and using the rain close to where it falls
3. Allowing water to soak into the ground (infiltration), if possible
4. Slowly transporting (conveying) water on the surface, i.e., in swales
5. Filtering out pollutants (water treatment)
6. Allowing sediments to settle out by controlling the flow of the water
7. Allowing some water to evaporate and be used by planting, i.e., through installation of tree pits, green roofs

Types of SuDS

Within the concept of ‘Sponge Cities’ (built environment which incorporates an abundance of natural areas such as trees, parks and lakes) and the development of blue-green infrastructure in urban areas, SuDS in simple terms collect water and filter it slowly, lowering and delaying flow rates, into the ground, rivers or the sewerage system.

A wide range of SuDS exist including attenuation basins, swales, permeable pavements, soakaways, rain gardens, filter strips, and green roofs. Here are some of the most effective types of SuDS to consider…

Swales

A swale is a shallow, vegetated channel designed to store and convey surface water runoff slowing the flow while removing pollutants. It could be part and focus of an urban landscape for example as part of a pedestrianised area. There are two types of swales that could be utilised:

Dry Swales

A dry swale is usually dry and will fill with water during a rainfall event, releasing it back into a piped system after the event and returning to its dry state.

Wet Swales

A typical wet swale does not have an underdrain and water is visible in all rainfall events. Any additional SuDS features within an area could drain towards and outfall to these swales

Raingardens & tree pits

Bioretention systems are shallow landscaped depressions which are used to reduce runoff rates and volumes and treat pollution (e.g. along highways and in public open spaces). They can form attractive landscaping features within the urban environment and help create a sense of place. New trees can be planted within tree pits as standalone features or part of bioretention systems to improve their performance.

Green roofs

Green roofs are roofs covered with vegetation. Various types of green roofs exist, providing a range of benefits depending on their nature: they can be shallow and lightweight, covered with grass or sedum (e.g. extensive green roofs) or proper roof gardens including plants and trees (e.g. intensive green roofs). Green roofs are a great solution in dense urban environments where space is at a premium.

Success in sustainable drainage requires a co-ordinated inter-disciplinary approach to water resource and green space management from institutional organisations, industry and academia, as well as local communities and stakeholders. With a multi-disciplinary skill set across different specialisms, and cross-border collaboration between our many water experts in the Nordics and wider Europe, Sweco can deliver all phases of SuDS design, from feasibility study to construction support. Contact us below to discuss your specific challenges and requirements.

Water management is about more than water management alone

To ensure sustainable quality of life in liveable and attractive cities, we need to draw on many different ideas and perspectives on water management from professionals across multiple disciplines – as well as citizens – prioritising Nature-based Solutions and a holistic approach to Placemaking where possible.

Sustainable drainage systems present valuable opportunities to enhance developments for people, places, and the environment. Key to maximising the benefits SuDS is considering Placemaking must-haves in the design process at the earliest opportunity with landscape architects, ecologists, air quality and pollution experts and transport planners wherever possible.

A team of teams approach

Without a proactive and collaborative ‘nature in the round’ mindset, there is a risk of missing valuable opportunities, leading to poor outcomes like unattractive, isolated and fenced-off elements that fail to fully contribute towards climate change mitigation, social value, and the enhancement of the urban landscape.

Integrating SuDS for a sense of place

• Air quality improvements for community health
• Reduced heat island impact
• Biodiversity net gain