A Genuinely Innovative Answer to an Escalating Urban Water Management Challenge
For many older cities and towns, sustainable water management has been steadily rising up the agenda for years. Existing ageing infrastructure built for a different era and population, coupled with increased hardscape areas and roads for today’s living means that drainage infrastructure in some areas is at or above capacity. Heavy downpours result in the system being overwhelmed resulting in flooding and associated pollution and damage.
The harsh reality is that options to increase the capacity of existing drainage pipe networks are very expensive and unsuitable in the face of climate change.
What can be done, however, is develop sustainable and resilient SUDS systems that mimic natural drainage, allowing surface run off to be managed as close to the surface and as close to its source as practicable.
‘Greener Grangetown’ does just that, by re-landscaping the urban realm with soft landscape and SUDS interventions.
Greener Grangetown in Cardiff is a very interesting example of the successful retro installation of SUDS features into an existing urban streetscape. The work was commissioned by City of Cardiff Council, Dŵr Cymru Welsh Water and Natural Resources Wales and led by Arup. - Arup's water engineers and placemaking team designed solutions that integrated SUDS with public realm improvements, with GreenBlue advising on the tree pit installations, and assisting the GG team from concept through to completion.
The Greener Grangetown project is located in one of Cardiff’s most densely populated wards. The project area runs alongside the infamous Rivers Taff, Wales’ busiest cycle network. Work was undertaken on 13 streets: Aber St, Abercynon St, Bargoed St, Blaenclydach St, Coedcae St, Clydach St, Cymmer St, Ferndale St, Llanbradach St, Taff Embankment, Taff Terrace and Ystrad St.
Prior to the commencement of this scheme, the rainwater flowed into the sewer, mixed with wastewater from kitchens and bathrooms and was pumped around 8 miles to the Vale of Glamorgan, before being treated and released out to sea. By removing this rainwater from the sewer, Dŵr Cymru Welsh Water has reduced the energy used for pumping and treating the wastewater. At the same time, by doing this, they have freed up some space in the sewer to help the region adapt to more extreme weather conditions which are caused by climate change.
A Solution with Multiple Physical, Social and Economic Benefits
As well as slowing the flow, cleaning water naturally and reducing the financial and carbon costs of pumping wastewater, a key goal was to ensure that Greener Grangetown delivered a wide range of other of economic, social and environmental benefits.
Martyn Evans, Project Lead from Natural Resources Wales, said
“The new street designs included installing attractive rain gardens and kerbside planting areas. These not only enhance local biodiversity and wildlife, but deliver important improvements to water quality in the River Taff, and encourage water efficiency. By creating more green areas we’ve opened up new opportunities for people to enjoy walking, cycling and other recreation close to where they live and work. More greenery and tree planting also means noise and pollutants are better absorbed, and air will be cleaner too.”
Green Infrastructure will encourage Modal Shift ©GreenBlue Urban
As well as forming part of the rain garden strategy, the trees and shrubs bring a cohesive identity to the Greener Grangetown area.
The layout, species, shapes and colours of the planting gives each street an individual look. In total, 135 trees have been planted – and a total of 19 different species.
All the trees share certain characteristics. They are:
- Generally deciduous so that natural light is maximised during the winter.
- ‘Street trees’ that can tolerate urban environments.
- Trees that provide interest all year round either due to leaf colour, bark or flowers.
- All trees are UK provenance
- Trees with appropriate root volume provision, and designed for long term tree health
- Trees with a 2.5 metre clear stem to ensure establishment and deter vandalism.
- Tree species with a high biodiversity value.
The Arup design team, working alongside tree officers at the City of Cardiff Council, urban tree and soil science specialists at Natural Resources Wales and GreenBlue Urban Ltd, put a design emphasis on long term sustainable tree planting for the raingardens and tree pits. Where possible, tree pits were linked below ground, increasing available soil volume for the trees, and simultaneously increasing water attenuation capacities, a true win-win.
Load bearing soil cells from GreenBlue, were used extensively to provide load bearing soil volume, and maintain uncompacted aerated soil conditions, perfect for root growth, water attenuation and transport, and air supply in the root zone.
StrataCells for Linked Tree Pits Image ©Arup.
Uncompacted soil media is vital in these situations – as tree health depends on the macro and micro pore structure within the soil. The structural components such as RootSpace and Stratacells look after the physical structure of the soil, enabling the soil to look after the tree. This simple philosophy has served urban tree planting projects very well since first introduced globally by GreenBlue Urban back in 2001.
The Client Project Lead from Cardiff Council and instigator of the scheme Ian Titherington stated:
Green Blue’s input into the project has been a critical element, in delivering a truly green environment into streets previously largely devoid of such advantages. Working alongside our excellent design team from Arup, they have helped to already transform the street scene and peoples’ perceptions of the area; this being achieved before the trees have been located for more than two seasons.He concluded,
“The success of this project must be judged on its ability to be a catalyst for many other similar schemes, and properly designed urban tree systems like Green Blue’s designs are to my mind essential, in delivering the multi-benefits that urban retrofit projects must deliver for their communities.”
Completed Rain Garden Image ©Arup.
GreenBlue Urban have enjoyed being part of the team making this scheme happen. From the earliest concept stage, experienced design consultants contributed to detailed drawings, and followed through, working with the contractor and providing active ‘on site’ support during construction. We continue to be involved as the project planting establishes and matures, for no other reason other than it inspires us! The GreenBlue mission is to ‘enable sustainable cities through Green and Blue Infrastructure’. Greener Grangetown is an exemplar of this vision and mission fulfilled.
The results so far have been overwhelmingly positive. The team have been hugely enthused about delivering such a broad spectrum of both physical ecosystem and social benefits through this well-planned scheme. As a GreenBlue representative put it
“the trees and landscaping in this project are raising the living standards for so many people, and the nice thing is that because the Greener Grangetown team have invested in appropriate volume tree pits, the value is going to increase year on year for decades to come.”