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Flooding 5: Sustainable Drainage Systems (SuDS)

aerial view from South Kensington across Albert Hall to Kensington Gardens, sunny day

Suitable for GCSE and A level

In most drainage basins, infiltration allows rainfall to soak away naturally. Only if soils are impermeable or if the ground is frozen does infiltration slow down or stop. However, the UK is heavily urbanised and urban drainage basins are full of impermeable surfaces of tarmac, brick and concrete where natural infiltration is prevented. As car ownership increases there has been a trend in many larger cities to pave over front gardens to create additional off-street parking. It is estimated that two-thirds of London’s front gardens are now paved. This further reduces the capacity for natural infiltration in our cities.

Our towns and cities are protected by drainage systems and culverts which are designed to remove surface water quickly and keep our streets dry. During extreme rainfall events these drainage systems can have unintended consequences:

  • They sometimes allow pollution from roads (such as oils) and foul water to be washed into rivers.
  • If they are blocked or inadequate, they can back up, causing surface water flooding in the street. It is estimated that around 4 million households in the UK are at risk of surface water flooding.

These issues can be tackled using Sustainable Drainage Systems (SuDS) schemes. The British Geological Survey provide a brief outline of SuDS here. The Environment Agency works with partner organisations such as Susdrain to improve drainage and reduce the risk of surface flooding in urban areas. Sustainable Drainage Systems can be planned into new urban developments or retrofitted. SuDS have multiple benefits:

  • reducing flood risk in urban areas
  • improving water quality in rivers
  • increasing biodiversity
  • improving the public amenity value of a site by creating green or blue corridors through the urban environment.

The organisation which takes lead responsibility for managing the risk from surface water are the Lead Local Flood Authorities (LLFAs). LLFAs (unitary authorities or county councils) are responsible for developing, maintaining and applying a strategy for local flood risk management in their areas and for maintaining a register of flood risk assets. LLFAs produce guidance notes on the use of SuDs for managing the risk of flooding from surface water and work with developers to approve, adopt and maintain SuDS features in new developments.

Specification requirements

The movement of water through a drainage basin is the focus of several GCSE specifications and river management is a feature of all of them. Download the GCSE specification audit.

River processes and landforms do not feature in the A level specifications. However, the concept of the drainage basin as a system is common to all. In particular, this resource will help students understand the relationship between stores and flows. Download the A level specification audit.

Learning objectives

This resource can be used to meet one or more of the following objectives:

  • consolidate prior learning about flows and stores within the drainage basin
  • investigate ways in which natural processes within the drainage basin can reduce the risk of flooding.

Download the Assessment Objectives.

GCSE activities

Understanding SuDS provides an another opportunity to consolidate prior learning about the stores and cycles that exist within every drainage basin. Students should watch the short animation, Ever wondered where the rain goes?, to understand the principles behind SuDS. The first minute of the video provides a simple but effective summary of the movement of water through a natural drainage basin. You could ask students to create a commentary for this part of the animation that includes geographical terms such as infiltration, throughflow and evapotranspiration. Students could use the remaining part of the video to engage with the following enquiry questions:

  • How can urban areas be modified to improve infiltration and slow the flow of water?
  • What are the advantages of planting trees in urban areas?
  • How might local residents benefit from SuDS?
  • How might SuDS help us adapt to a changing climate?

SuDS schemes are a tangible example of sustainable urban development with benefits for wildlife, recreation, and physical and mental wellbeing of local communities. A video of the Derbyshire Street Pocket Park scheme in Bethnal Green London and this worksheet will help students evaluate the community benefits of this scheme.

  • How did the scheme change the urban environment?
  • How does is it help to reduce the flood risk?
  • How might the scheme improve quality of life for local residents?

SuDS provides an opportunity for students to design a fieldwork investigation within the school grounds or within a neighbouring residential area. Note that fieldwork carried out within the school’s grounds would complement but must not replace the two statutory fieldwork opportunities that must be offered to GCSE geography students. High Water Films have a collection of short videos about flood risk management on their website including one about SuDS for schools.

A level activities

The Susdrain website includes an interactive map of the UK which contains details of SuDS case studies. The Derbyshire Street Pocket Park scheme in Bethnal Green, London, provides a detailed description of a small-scale SuDS project that students can evaluate.


Other lessons in this series:

Flood risk and flood management: Introduction
Flooding 1: Causes of river floods
Flooding 2: Investigating the effects of river floods
Flooding 3: Response to floods: Oxford Case Study
Flooding 4: Managing the upper drainage basin
Flooding 6: Managing river floods – exploring the role of the Environment Agency
Flooding 7: Coastal flooding at Chiswell
Flooding 8: Managed realignment
Flooding 9: The role of the Environment Agency in coastal management and the development of shoreline management plans

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