Case Study: Greener Grangetown – retrofitting sustainable drainage

Greener Grangetown is a partnership between Cardiff Council, Welsh Water and Natural Resources Wales.

The idea:

Cardiff Council’s Victorian sewerage system pumped gallons of rainwater that collected in road drains from the Riverside area of Grangetown to a distant treatment works before it could be safely returned to the sea. One drainage engineer spotted that, with minimal on-site treatment, it could be safely left to drain into the nearby Taff, lessening the pressure on pumping stations and saving expensive treatment processes.

What happened?

The project had stalled at Cardiff Council, but Welsh Water and Natural Resources Wales had suggestions for how it could fulfil their objectives too and the idea shifted and grew.

Sustainable urban drainage systems (SUDS) that use green infrastructure (plants and trees) to make surface water safe and reduce flooding risk, have long been seen as beneficial but have only been tried in new developments or retrofitted in wide boulevards. Grangetown’s Victorian terraced streets presented the perfect opportunity to demonstrate that SUDS could be used in more densely-built areas.

As a multi-functional project, it was hard to pull the funding together. The organisations were not used to using siloed funding pots in this way. But with pooled funding agreed from the start, and some money from a Landfill levy, they were able to get it off the ground and keep it going even as personnel changed.

With a clear and distinct brand, ‘Greener Grangetown’, and genuine public consultation (including a full time liaison officer on-site) the three partners were able to have a productive and positive relationship with local residents. A local couple came up with a key idea for positioning the greenery and prevent local parking problems. Because local people were very involved in the design process from the early stages, levels of parking vs greenery, locations and types of trees and street furniture could be varied to meet residents’ needs and desires on a street-by-street basis, which improved the environment and created a sense of ownership.


  • Unexpected partners can revive a stalled idea, with new ideas and new funding streams, but public sector budgets are not necessarily set up for multi-agency projects.
  • For an infrastructure project, it took an unusually holistic approach to improving the neighbourhood. Involving a wide range of partners and local people early in decision-making meant the project could improve a cycling route, help solve problem parking and reduce crime among a range of other issues as well as drainage.
  • Because the drainage project is so cutting edge, the building contractor’s workers have been upskilled.

What’s next?

Visitors from across the UK and Europe have come to see how they can implement sustainable drainage in their own areas. Cardiff Council has undertaken to use the expertise to become a UK leader in SUDS, incorporating the ideas into proposed changes to Lloyd George Avenue in Cardiff.

Image: Arup