The Greener Grangetown project in Cardiff utilized sustainable urban drainage systems (SuDS) to transform the urban environment. The project incorporated rain gardens, tree pits, permeable paving, and combined kerb drainage and channel drainage. The benefits of the project included the removal of 4.4 Ha surface water from the combined sewer, the planting of 127 new trees, the creation of 1,700m2 of new green space, and the establishment of 108 rain gardens. Additionally, the project improved road safety, created a new bicycle street, and enhanced the public realm with new street furniture and surfacing. The estimated value of the wider benefits of the project is over £8.4 million.

The Challenge

Grangetown, located near Cardiff city centre, faced challenges with its Victorian-era drainage system. Surface water entered the combined sewer network and was pumped for 8 miles before being treated and discharged into the Severn Estuary. The aim was to remove surface water from the combined sewer network, reducing operational costs and providing resilience against climate change and urbanization.

The Solution

The project introduced 108 raingardens containing native trees and plants to improve water quality. The rain gardens and tree pits acted as bioretention systems. The Greener Grangetown initiative removed an average of 40,000m3 of surface runoff from the combined sewer system annually. The design also considered the local community's needs, such as parking availability and litter management.


The project transformed the public realm, environment, and transport infrastructure. It provided multiple benefits, including water management, regeneration, and the transformation of a busy cycle route. The project performed well during extreme weather conditions, demonstrating efficiency in reduced operational costs and environmental benefits.

Key Learnings

  1. SuDS can be delivered anywhere: Despite challenges like utilities, limited free space, topography, and existing infrastructure, SuDS solutions can be engineered.
  2. Materials and products: There's a need for more 'off the shelf' products tailored for rain garden features.
  3. Pre-construction phase and Contract type: Early involvement of all stakeholders is crucial. The type of contract used posed financial challenges due to the retrofit nature of the project.
  4. Community engagement and communication: Engaging the community is vital for retrofit projects. The community's feelings and participation are key indicators of a project's success.

Further Developments

Research is being conducted to analyse water quality improvements, with a focus on microplastic removal. Cardiff University is also researching the health and wellbeing benefits to the community from an improved local environment.

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