As urban development expands, the risk of surface water flooding increases. Sustainable drainage systems (SuDS) are designed to control surface water close to where it falls and mimic natural drainage as closely as possible. There are several types of SuDS which work to manage the risk of flooding, whilst providing additional benefits for people and the environment.
Sustainable drainage systems, or ‘SuDS’, aim to manage surface water locally and are a natural alternative to traditional drainage networks like pipes and sewers. SuDS provide opportunities to:
Click here for information from the Royal Horticultural Society on how SuDS can manage waterlogging and flooding in your garden.
Click here to view our ‘Sustainable Drainage Systems (SuDS) Toolkit’ which contain a variety of resources that are available to download.
Bioretention strips are vegetated areas with sand and gravel beneath. As rainwater falls on them, runoff will either infiltrate through, or drain into a pipe which carries the water elsewhere. The storage and diversion of rainwater can reduce peak runoff rates which manages the risk of flooding. During the infiltration process, the bioretention strips filter and cleanse the runoff from pollutants, nutrients, metals, suspended solids and bacteria, which improves the overall quality of the stored water.
Bioretention strips have been used in this project, GrowGreen Manchester, as tree pits which absorb the rainwater which falls on the footpath above them. Click here to read the case study.
Detention basins are storage basins on open areas of grass that are typically dry, except during a storm event. They store rainwater and surface water runoff, before allowing it to slowly infiltrate into the ground, reducing the risk of flooding to the local area. They also filter the water to remove sediment and pollutants, thus increasing water quality.
Detention basins can serve as both a sustainable drainage system and as recreational areas. When wet, they retain water and can be beneficial for wildlife which will increase the area’s biodiversity. When dry, the area is a safe space for leisure activities, and both may be useful as an educational resource.
Retention ponds are areas of open and shallow water designed to store rainwater and attenuate runoff at a controlled rate during and after a rainfall event. They differ from detention basins as they are intended to hold water permanently, with the water level rising temporarily during heavy rainfall to accommodate for more water.
Green roofs, or ‘living roofs’, are fully or partially covered with vegetation. They have a multi-layered system comprising of an impermeable layer, a drainage layer and a ‘living’ layer made up of plants and vegetation. The vegetation intercepts and stores rainwater to reduce the amount of runoff entering drains and sewers which can contribute to reducing flood risk. A green roof is typically low maintenance and can sometimes be used to replace a traditional roof on buildings such as garages or bus shelters.
Permeable paving is an alternative to traditional concrete paving and allows for surface water runoff to infiltrate the ground, thus managing surface water flood risk. Permeable paving either uses gaps between paving stones to allow water to run through, or the paving itself is made of a porous material that allows water to infiltrate through. Other alternatives to paving which have the same effect include wood chippings or recycled aggregates. Surface water infiltrates through the soil below, or into a storage tank beneath the paving where it can be slowly released.
Rain gardens are small, shallow depressions of vegetation which can withstand being inundated with water for up to 48 hours. They receive surface water runoff from impermeable surfaces like roofs, driveways and roads. Downpipes from roof gutters and channel drains can be redirected away from sewers and redirected into these gardens. Rain gardens are an infiltration method that allows runoff to accumulate and increase the amount of water flowing through the soil which reduces rates of runoff and volumes of surface water. As the runoff infiltrates the ground, pollutants and sediments are filtered out which improves the water quality.
Rainwater harvesting involves collecting and storing rainwater that would usually flow into drains and sewers. Rainwater that has been collected can be re-used in your home and garden for purposes such as, irrigation, toilet flushing and gardening.
Water butts are a common rainwater harvesting option which can easily be retrofitted to properties. They can be fitted to the downpipe of a building to collect the water which falls onto the building’s roof. The connector kit diverts rainwater from the downpipe through a small section of pipe leading into the water butt. When the water butt is full, excess water tracks back up the small section of pipe and over-flows back down the drainpipe to the drainage network as normal. A small tap located at the bottom of the water butt allows buckets and watering cans to be filled.
Tanks, geocellular structures and plastic crates beneath the ground can also be used for storing rainwater. They can then be used to convey and infiltrate the water to reduce peak flows by facilitating natural drainage. Only a certain amount can be discharged back into the environment to manage the risk of flooding.
Swales are shallow, broad vegetated channels. They provide temporary storage, infiltration, and conveyance of stormwater runoff to reduce peak flows in watercourses and drainage systems.
Swales can be ‘wet’ and store water above ground in the channel, or ‘dry’ where water collects in a pipe or gravel layer beneath. In wet weather, rainwater flows down the sloped sides and into the swale channel where it infiltrates through the vegetation, which filters sediment and pollutants. Some of the runoff is also lost at the surface through evapotranspiration.
Wetlands are similar to retention ponds and are shallow, marshy areas filled mostly with aquatic vegetation. Wetlands attenuate and slow the flow of rainwater runoff, whilst filtering the water and improving its quality before it enters local watercourses. They remove fine sediments, dissolved nutrients, metals and particulates from the water by filtration through the vegetation and aerobic decomposition.
Image: Castle Irwell Flood Plain & Salford Wetlands cc-by-sa/2.0 – © Colin Park – geograph.org.uk/p/6014644
Under the National Planning Policy Framework, SuDS should be provided on all major developments (these include ten or more homes, or on areas of 0.5 hectares or more), and in areas at risk of flooding unless demonstrated to be inappropriate (for example, mineral extraction development), and the techniques used will depend on site-specific characteristics.
For more information, please visit our Planning and Development page here.
United Utilities are working with housing developers across the North West to create sustainable and greener developments. With a projected 310,000 more homes expected to be built in the region by 2030, United Utilities are looking for innovative ways to make the North West more resilient. United Utilities’ Environmental Infrastructure Scheme is available for housing developers and offers a 90% reduction in infrastructure charges, providing the homes built are water efficient, with measures to reduce households’ water usage to 100 litres per person per day (lppd).
In addition, a reduction on wastewater charges is also available for properties that do not connect their surface water drains to the existing sewer network. These plots that sustainably discharge surface water can save the developer up to £523 per new plot. The region’s watercourses will benefit in improved water quality as surface water runoff will be redirected to sustainable drainage system alternatives which allow runoff to soak away naturally, and the homeowner will benefit from a reduction in their bill.
The environmental infrastructure scheme aims to ensure that the properties built today are more resilient to the extremes of climate change.
Click here to read more on the Environmental Infrastructure Scheme.
Blue-green infrastructure aims to manage the risk of flooding, whilst introducing a more natural water cycle into urban environments and allowing multi-functional land use to benefit the environment, society and the economy. The natural water cycle is characterised by high evaporation, high infiltration and low surface water runoff. Blue infrastructure includes features that retain water, such as detention basins, ponds and wetlands. Green infrastructure applies to natural land, woodlands, domestic gardens, green open space and parks.
Blue-green infrastructure can provide many benefits and ecosystem services, such as:
As the climate changes and the population increases, blue-green infrastructure will be crucial to the wellbeing of the communities who live and work in our towns and cities. Such techniques are an important measure in reducing the likelihood of traditional drainage systems becoming overwhelmed and flooding many properties. Creating green and open and spaces will not only have positive effects for flood risk, but it will benefit the amenity of an area, providing attractive, useable space for communities.
Download this ‘Blue-green Infrastructure’ resource here.
Sustainable drainage systems (SuDS) often provide a range of benefits to people and the environment, from managing flood risk to improved water quality and increased biodiversity.
Hover over each benefit below to explore the multiple benefits of SuDS. You can also find this information below the image or by clicking the benefits within the menu on the left-hand side of this page.
You can download the full resource with explanations here.
SuDS mimic natural drainage patterns which reduces the volume of runoff and rainwater reaching drains and watercourses. They provide areas to store water and slow the flow of water to manage flood risk in urban areas.
SuDS such as water butts can collect and store water all year round which can be reused during the summer and in periods of drought, for numerous different purposes, such as toilet flushing, irrigation, or watering plants. Not only is this better for the environment in terms of water availability and usage, it can also help to reduce your household’s water bills.
Using SuDS such as rain gardens, detention basins, wetlands and retention ponds can help to maintain, link and create new habitats to support existing and new wildlife. This increases the biodiversity in areas and improves the quality of ecosystems. Some SuDS could also be used as an educational resource for local schools and nurseries, where they can observe different plant and animal species which they may not have had the opportunity to do before, especially if the school is located in an urban area.
SuDS can often increase the physical and mental health and well-being of communities by providing access to open, green spaces that allow for activities such as walking, cycling and organised sports. Some SuDS measures, for example, green roofs, green walls, or swales can improve the air quality of an area as they absorb or remove pollutants, including nitrogen dioxide (NO2), sulphur dioxide (SO2), particulates (PM10) and ozone (O3).
Large, open spaces and greater use of trees and plants can increase the aesthetic value of an area, especially in urban areas and city centres where green space is at a minimum. It also attracts tourists and adds value to housing and land prices, boosting economic growth.
As rainwater infiltrates, SuDS filter fine sediments, and dissolve nutrients, metals and particulates from runoff which improves the water quality. They also intercept rainfall and reduce the volume entering sewers and drains, which reduces combined sewer overflow and the amount that needs treating.
The vegetation and plants used in SuDS such as green roofs, can capture and store carbon and greenhouse gases to improve air quality. They can reduce air and water pollution and also regulate building temperatures which can help reduce the urban heat island effect.
Surface water flooding, also known as pluvial flooding, occurs when the volume of rainfall exceeds the capacity of drains and sewers. The excess rainfall cannot soak into the land or drain away through drainage systems, and instead, flows over the land. The intensity of this flooding can be increased by blocked road gullies or sewers, saturated and waterlogged land and an increase in hard, impermeable surfaces. It’s important to consider the cause of the surface water flooding at your property when installing SuDS measures, as it may help you decide what measures are the most appropriate to install to tackle the issue.
To learn more about surface water flooding, view our toolkit here where you can find a number of useful resources:
Click on the links below to download the case studies which are great examples of how SuDS have been used across the North West.
The Crossens solar-powered pumping station project is a regional first for the Environment Agency (EA). The station will be powered by solar energy with surplus energy produced. This energy will be stored for future use across EA infrastructure. The station will continue to reduce flood risk to 660 homes and farmland.
United Utilities are responsible for managing and slowing rainwater surface runoff, which they do by installing Sustainable Drainage Systems, otherwise known as SuDS. SuDS can slow rainwater runoff by mimicking natural drainage through interception, infiltration and evapotranspiration, which can help manage a catchment’s flood risk. SuDS are a vital part of United Utilities’ wider Catchment Systems Thinking (CaST) approach, which manages the catchment in a more holistic and integrated way and also considers the environment and people together.
Blue-green infrastructure acts as multi-functional sustainable systems which encourage water to flow more naturally by mimicking natural drainage. In turn, blue-green infrastructure reduces the demand on the drainage network by slowing and storing rainwater which would run off into the sewer network. Blue-green infrastructure incorporates green spaces, which are vegetation-based features such as trees, hedgerows, permeable paving, and water-based blue features such as ponds, wetlands and floodplains. The benefit of installing blue-green infrastructure is that natural drainage is improved, which manages surface runoff more effectively than traditional grey infrastructure, therefore reducing flood risk.
Click here to visit the Unpave the Way project page. Unpave the Way is an innovative project between the North West Regional Flood and Coastal Committee (North West Regional Flood and Coastal Committee | The Flood Hub), the Environment Agency, United Utilities, and Lancashire County Council which aims to inspire greener gardens through Sustainable Drainage System methods like permeable paving and rainwater harvesting.
Image: Environment Agency
United Utilities created a SuDS ‘slow the flow’ garden for RHS Tatton Show, which is shown in the video below. It featured permeable paving, rainwater harvesting tanks, a green roof, bioretention strips and permeable concrete walkways.
Watch United Utilities video above for a tour of the Slow the Flow garden.
Gardens play a vital role in managing the risk of surface water flooding, and FloodRe’s The Flood Resilient Garden will showcase how specially chosen landscaping and planting features can respond and adapt to heavy rainfall and surface water flooding. The project garden is due to be shown at Chelsea Flower Show 2024.
Click here to find out more about FloodRe’s The Flood Resilient Garden. You can view The Flood Resilient Garden’s Instagram page here.
