Retrofitting a sustainable urban drainage system, transforming the public realm with trees and planting and creating Wales’ first cycling street along National Cycle Network Route 8.
Feasibility study: 2012/13
Public Consultations: 2014 & 2015
Final Design: 2017
Grangetown, Cardiff city centre, Wales, UK
What problem did it address?
The site comprises 13 streets on the bank of the river Taff, close to the centre of Cardiff. The drainage network was unsustainable. Rain water that landed on the roads and roofs entered the combined sewer system and was pumped 8 miles to a treatment facility.
The sewer and drainage networks need to respond to a growing population and extreme weather events caused by climate change.
How did it do it?
An integrated Green Infrastructure approach brought together civil engineers and landscape architects.
The project team needed to address the sustainable drainage challenge. It used this as a driver to improve the environmental quality of a streetscape.
Engagement with the community was ongoing through from the feasibility stage right through to construction. This ensured that the measures met the residents’ needs and aspirations. Drop-in sessions, leafleting and social media were part of the engagement. The project team also involved the community in the design of their streets. Planting events involved local schools and residents.
Rain gardens mimic natural processes and represents a more natural way of catching and cleaning rain water. This form of sustainable drainage provided extra wildlife habitats.
The design team sought a long-term sustainable approach to tree planting for the raingardens and tree pits. This included selecting trees for tolerance to water and air pollution and providing the best conditions for tree health. Allowing water borne pollutants to filter through a healthy uncompacted growing medium reduces the transmission of these pollutants by up to 95%, allowing the treated water to be discharged directly into the river.
Who has it benefitted and how?
Improving the quality of the public realm for 13 streets directly benefits about 500 residents. Improving active travel infrastructure benefits the wider city.
Measures have delivered a more sustainable and resilient sewer network by removing 42,000 cubic metres of surface water annually from the combined wastewater network.
Cyclists in this very busy part of Cardiff have benefitted from increased safety and a pleasant, healthy environment.
What is the cost and how was it funded?
A detailed feasibility study in 2013 calculated an annual benefit of £381,760, including water management, ecosystem services, health and wellbeing. This was instrumental in securing scheme funding of £2.5m from project partners Cardiff Council, Dŵr Cymru Welsh Water
and Natural Resourced Wales. Funding was also secured from the Landfill Communities Fund, a scheme allowing landfill operators to contribute towards eligible local projects.
Evidence of success
The project has created a healthy and resilient local environment that supports economic and social prosperity. It embedded a broad range of Green Infrastructure benefits in the public realm improvement work.
The project created 1,700m2 of new green space, including 108 rain gardens and a community orchard. The project also planted 127 trees contributing to noise reduction, better air quality and carbon sequestration.
The 555m long bicycle street contributes to the UK National Cycle Network Route 8 and the Taff Trail Active Travel route in the heart of the Welsh capital city. Taking cars out of this busy section improved cyclists’ safety.
The water drainage system has been adopted by Cardiff Council. Their Parks Department cares for the long-term maintenance of the above ground elements of the planting.
The Project won the ‘Engineering Project of the Year’
2018 UK Water Industry Award.
Difficulties and challenges
A key design challenge included the presence of utilities within streets more than 100 years old. This was overcome by engaging with utility providers early in the design process. The project team agreed measures to work around utilities and provided designs that could be adapted on site if required.
Working within a community was also a challenge, but also a big opportunity.
The project faced challenges completing the central strip of the bicycle street on time while retaining a live highway and cycleway. To overcome this a coloured, imprintable thermoplastic surfacing was used instead of traditional stone or tar-mac, which avoided several weeks of disruption.
Howard Gray, GreenBlue Urban 07880 400947
Greener Grangetown website https://greenergrangetown.wordpress.com
Case study by ARUP https://www.arup.com/projects/greener-grangetown
Case study by GreenBlue Urban https://www.greenblue.com/gb/case-study/greener-grangetown/
Presentation: Sustainable Drainage Systems and Greener Grangetown, Natural Resources Wales, 2018 https://cdn.naturalresources.wales/media/687377/greener-grangetown-2018.pdf
Cardiff City Council
Dŵr Cymru Welsh Water
Natural Resources Wales
ERH Communications & Civil Engineering (Contractor)
GreenBlue Urban (Tree root cell system supplier)