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What are SuDS?

Sustainable Drainage Systems (SuDS) can be groups or individual features that manage rainwater to minimise flooding and pollution. They mimic the natural water cycle by allowing water to be collected in the ground, stored and then slowly released back into the drains. Some SuDS can be designed to release the water in to the soil through a process called infiltration, and removes the need for drains. Lambeth's clay soil prevents the use of infiltrating SuDS and so the borough will always be heavily reliant on the combined sewer network to drain.

Good SuDS design seeks to provide four pillars of benefits. Water quality, water quantity, biodiversity, and amenity. These, respectively, reduce pollution, reduce the risk of flooding, provide more greenery and habitats, and improve landscape aesthetics. This supports overall environmental resilience in urban areas, such as helping to reduce the urban heat island effect and poor air quality. 

The four pillars of good SuDS design 

The SuDS Manual (C753): CIRIA (2015)

Common SuDS incorporate features such as:

  • Rain gardens - These are green areas with planting that can withstand temporary excess water. These range in size from 1 square meter to 100s. 
  • Green roofs/walls - these are typically flat roofs or walls with planting which slow down the pathway of the water before going into the guttering.
  • Rainwater harvesting and water butts- these can hold the water from guttering and be used before going into the ground or drainage system. 
  • Ponds and swales - these are larger green areas that are designed to temporarily store water during storms but are mostly dry throughout the year.

Current landscape of Lambeth - traditional drainage

In the mid to late 1800s Lambeth's rivers were converted in to a sewer network. This has resulted in all our rain water and waste water being drained by the same system. Currently the majority of the borough is covered by hard surfaces like roofs, roads and patios which do not allow rainwater to drain into the ground. The remainder of the borough, like our parks also drains into this sewer as they have no open rivers to drain to. This produces a lot of water on the surface when it rains which very quickly enters the old Victorian sewer network. As a result the sewers cannot cope and become overwhelmed, flooding out on to streets and in to homes. During heavy rainfall the sewer is released in to the River Thames to help cope with the volume and rate of storm water. These releases are known as Combined Sewer Overflows (CSOs) and prevent large scale flooding but contribute to the poor health of our rivers.

With climate change the severity and frequency of storms will worsen. 

Future landscape of Lambeth - with SuDS

With initiatives like Soak Up Lambeth, we can capture the rain water as close to where it falls. This reduces the amount of water reaching the combined sewers, and therefore prevents it from accumulating in the low spots and flooding homes and businesses. 

Not only will SuDS help to reduce flood risk, but also depaving (i.e. removing) our impermeable surfaces  can, such as removing our paving slabs for open gravel or planting so water can naturally drain in to the soil instead of in to the sewer. Planting trees and allowing those already planted to grow to their full potential helps to capture rainwater on their leaves, meaning less water reaches the sewers to cause flooding.

By creating a greener landscape in Lambeth we can help make it more resilient to climate change, provide more and better habitat for nature, all while making the borough a nicer place to live, work and visit.

The benefits of installing SuDS

  • Help manage the volume and speed of run-off water, reducing the downstream flow and destructive power of surface water flooding.
  • Improve water quality by filtering particulates and pollution before entering the River Thames or other wetland areas.
  • Encourage natural groundwater recharge, maintaining river and stream flows in periods of dry weather, therefore supporting wetlands downstream.
  • Create additional green spaces supporting the well-being of local people and communities and can increase the amenity value of the local area.
  • Incorporating more green spaces with planting and trees can provide more cooling and shade, increase evapotranspiration and help regulate climate impacts.

Further Reading

Find more information about SuDS at the UK Rain Garden Guide or visit susdrain.org for in-depth learning on rain gardens and Sustainable Drainage Systems.