With increased urban development, the risk of surface water flooding is also increasing. 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 many different types of SuDS which can not only reduce the risk of flooding, but also deliver many other benefits for people and the environment.
Sustainable drainage systems, or ‘SuDS’, are designed to control surface water close to where it falls and mimic natural drainage as closely as possible. SuDS provide opportunities to:
Some good examples of SuDS can be seen in this United Utilities video below of the sustainable drainage garden displayed at the RHS Tatton Flower Show. Find out more about the different types of SuDS in the following sections.
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. They are designed to channel, filter, and cleanse runoff vertically. The runoff can either infiltrate into the ground below or drain into a pipe which carries the water elsewhere. The storage of runoff and rainwater can reduce peak runoff rates which reduces the overall flood risk. Bioretention strips also filter runoff and remove pollutants, nutrients, metals, suspended solids, and bacteria, which has a positive effect on the overall water quality of the stored water.
Detention basins are storage basins on open, usually flat areas of grass that are normally dry, except during a storm event. They store rainwater and surface water runoff then allow it to slowly soak into the ground, reducing the risk of flooding to the local area. They also filtrate the water to remove sediment and pollutants.
Detention basins can serve as both a sustainable drainage system and a recreational area. When wet, they can be used as a pond for wildlife which will increase the biodiversity of the area and may be useful as an educational resource. When dry, the area is a safe space for leisure activities.
Green roofs, or ‘living roofs’, are roofs which are fully or partially covered with vegetation. They have a multi-layered system made up 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.
Permeable paving is an alternative to traditional concrete paving and allows for the infiltration of runoff to reduce 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 include wood chippings or recycled aggregates which have the same effect. The runoff infiltrates through to either the soil below, or into a storage tank beneath the paving where it can be reused.
Rain gardens are small, shallow depressions that receive runoff from roofs and hard surfaces and are made up of vegetation that can withstand being inundated with water for up to 48 hours. They are an infiltration method that allow runoff to accumulate in the shallow depression, increase the amount of water entering the soil whilst filtering out sediment and pollutants, and reduce rates of runoff and volumes of surface water. Downpipes from roof gutterings are often disconnected from sewers and redirected into these gardens.
Rainwater harvesting is the process by which rainwater that would usually flow into drains and sewers is collected and stored for later use. Rainwater can be collected from the roof of a house or from a tank beneath permeable paving where it can be re-used in your home and garden for irrigation, toilet flushing and gardening.
Water butts are a common rainwater harvesting option which can easily be retrofitted to buildings or garden sheds and connected to the downpipe to collect rainwater from the roofs. 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 for the filling of buckets and watering cans.
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 back into the ground to reduce peak flows by allowing natural drainage. However, this water must be treated before it is released and only a certain amount can be discharged back into the environment so that the risk of flooding is reduced.
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.
Swales are shallow and broad vegetated channels, which are flat at the bottom with sloping sides. They provide temporary storage, infiltration, and conveyance of storm water 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 of the swale, along its length and infiltrates through the vegetation, which acts as a filter, trapping sediment and pollutants. Some of the runoff is also lost at the surface through evaporation and transpiration.
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.
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.
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 generate benefits for 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. They are an important measure in reducing the likelihood of traditional drainage systems becoming overwhelmed and flooding many properties. Creating more open, green 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 often provide a range of benefits to people and the environment, from managing flood risk, improved water quality and increases in biodiversity.
SuDS mimic natural drainage patterns and reduce the volume of runoff and rainwater reaching drains and watercourses. They provide areas to store water and slow the flow of water to reduce flood risk in urban areas.
Sustainable drainage systems 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 could look at different plant and animal species which they may not have had the opportunity to do so before, especially if they’re located in an urban area.
SuDS can often increase the physical and mental health and well-being of communities through providing access to open, green spaces that can allow for activities such as walking, cycling and organised sports. Some SuDS measures, such as green roofs, green walls, swales etc, can also improve the air quality of an area and can absorb or remove certain 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 in city centres where there is not a lot of green space. 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.
Hover over each benefit below to explore the multiple benefits of SuDS. Download the full resource with explanations here.
Surface water flooding is also known as pluvial flooding and occurs when the volume of rainfall exceeds the capacity of drains and sewers and is unable to drain away through drainage systems or soak into the land, and instead flows over the land. The intensity of this flooding can be increased by blocked road gullies, drains and sewers, saturated and waterlogged land, and an increase in hard surfaces. It’s important to think about 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.