Sustainable Drainage Systems, or SuDS, are drainage systems that are designed to mimic the way that water would behave on a site if it were not developed, and it were still a green field. The rainfall should soak into the ground wherever it falls if possible so that it can nurture soils and plants and replenish aquifers. It can be captured in ponds and wetlands too, when there is space. On all sites, rainwater should be captured and reused in the buildings and the gardens, so that it doesn’t rush off the site and cause flooding downstream.
The 4 Pillars of SuDS
A good SuDS scheme will have four primary benefits, known as the four ‘Pillars of SuDS’. They are – managing the Water Quantity to reduce flood risk; managing the Water Quality to reduce pollution; delivering habitats for wildlife or Biodiversity; and creating green and pleasing places for people or amenities.
Water Quantity – this involves keeping as much water on site as practical and/or store it for a controlled release, this is commonly known as attenuation.
Water Quality – arguably the most important as the world is in crisis over clean water so treating water to the highest level is critical.
Biodiversity – design SuDS in harmony and sympathy with wildlife and plant life, its deliverability varies from project to project.
Amenity – designing SuDS to deliver benefits to the community such as a quality water feature, this often connects with biodiversity.
Flood & Water Management Act 2010
(Schedule 3)
SuDS are now the preferred drainage design method for all sites and many Planning Authorities will expect developers to include them in their projects. With DEFRA’s proposed enactment of Schedule 3 of the Flood and Water Management Act 2010, the inclusion of SuDS on all developments will become mandatory in England; this is already mandatory in Wales. The current focus on sewer overflows and the impacts of climate change mean that all developments should include SuDS, not just residential projects. SuDS are also being retro-fitted into our towns and cities when other construction projects are in progress and many local authorities are looking for opportunities to deliver them alongside schemes such as highway projects.
Water Quality
The Water Quality pillar of SuDS is SPEL’s specialty, and we are passionate about protecting our water resources across the globe. Fact: ‘only about 1.2% of earth’s water can be used as drinking water’ (National Geographic, 2023), so we must look after this precious asset. It is vital that SuDS schemes deliver good pollution control and the Simple Index Approach in the CIRIA SuDS Manual C753 will help us to do this using the Mitigation Index and designing the treatment train to this standard as a minimum. It’s key to understand how much pollution is in the runoff from the site, some sites where for example oil is stored or moved around the site, it will be necessary to manage the spill risk and this must be done first as it is at the ‘top’ of the SuDS Management Train.
Other devices include ponds, basins, and wetlands but care must be taken as these nature-based devices cannot be certain to deal with all pollution loads and most SuDS Treatment Trains will need to include a manufactured device. The CIRIA SuDS Manual C753 states that these devices must be installed upstream of any natural feature or attenuation tank to capture specific pollutants such as Total Suspended Solids (TSS), Metals, and Hydrocarbons while allowing the vegetation to thrive.
The SuDS hierarchy points to re-use and infiltration as the first stage of a good design with the use of rainwater harvesting, bio-remediation zones, tree pits and swales, allowing the water into the soil where pollutants are captured and broken down and the plants can take up some of the nutrients.
SPEL has a class-leading range of SuDS-certified systems designed and certified to meet most site applications and deliver exceptional water quality.
Each system ensures effective Mitigation of the 3 main pollutants (TSS, Metals & Oil) across the Pollution Hazard Index, this makes for simple specification and sizing of a treatment device that will deliver more than the required surface water quality standard as set out in the CIRIA SuDS Manual C753. By utilising SPEL certified products, engineers, developers, and local authorities can confidently implement sustainable drainage systems that have undergone rigorous testing and assessment and will maintain the treatment levels for decades to come.
At SPEL, we believe clean water is a right, not a privilege and we often don’t know it until we don’t have it, we must work together to provide for future generations. Sir David Attenborough said recently “Everywhere the availability of fresh water is becoming increasingly unpredictable and uncertain.”
Humanity can survive with higher temperatures, but we can’t survive without Clean Water, so start to safeguard this precious resource today.