Grey to Green

Integrated Infrastructures
An urban infrastructure strategy that combines green/blue infrastructure with economic and social benefits, reversing the modern infrastructural imagination to see the benefits of re-integrating ecology in cities


As places urbanise and buildings are built, soft and permeable land is paved with stone, brick, and tarmac—becoming an impermeable membrane between atmosphere and ground. Where rainwater once percolated directly down, now these hard surfaces shed it sideways, requiring complex infrastructural systems for its dispersal via pipes, channels, sewers, and outfalls. In cities that developed rapidly during the industrial revolution, the rising problem of drainage caused both by surface water and sewerage was dealt with via the construction of vast subterranean complexes.1Such as those developed by engineers Joseph Bazalgette in London and Eugène Belgrand in Paris. These highly-engineered urban waterways often dictated the forms of the city above—such is in the case of Bazalgette’s Thames Embankment. This typically meant hiding water underground, as a reaction to the visible, foul-smelling pollution of urban rivers, either by building over existing rivers or by constructing new, enclosed routes through water moves out of the city. This modern, industrial imagination saw the solution to hard infrastructure in more hard infrastructure—through separation and centralisation. 

Now, the population of industrial-age cities is vastly higher. Ongoing densification, an increase in car-based infrastructure, and the replacement of flexible surfaces with impermeable ones means ever-less opportunity for water to percolate naturally into the ground, leaving it nowhere to go. Alongside this, one effect of climate change is an increase in rapid and heavy rainfall: the same amount of rain falls, but in shorter periods, increasing the immediate demand on water infrastructure, and resulting in flash flooding where the drains can’t cope. In 2007, Sheffield experienced extensive flooding after a sustained period of heavy rain, with severe damage to life and property. 


In the face of this problem, Sustainable Urban Drainage Systems (SUDS) are designed to slow the flow, by providing areas of safe storage where water can remain near to the surface in order to ease pressure on systems further down the line. They usually integrate large, open areas of planting with extensive rooting zones and flush kerbs allowing water to run into filter zones. Beyond these, water is either fed slowly into the piped system, allowed to discharge into the ground, or it evaporates. One of the largest single city-centre SUDS schemes in the UK is Sheffield’s “Grey to Green” strategy, developed by Sheffield City Council as an integrated flood management, active travel, and economic development plan. It has to date converted several sections of redundant city-centre dual carriageway into a linear urban park2The first phase—around Sheffield’s law courts—was completed in 2016, and the second—Castlegate—was completed in 2020. totalling 1.3 kilometres of new footpaths and cycleways—converting car infrastructure into public space and active travel infrastructure along the way. 

The scheme has been designed by Sheffield City Council with Robert Bray Associates—landscape architects who specialise in SUDS—working in close interdisciplinary collaboration. Planting, suited to both waterlogged and drought conditions and tolerant of the kinds of chemicals that run off urban surfaces, has been designed by Nigel Dunnett and Zac Tudor to promote biodiversity. The scheme integrates much of the knowledge developed at Sheffield University’s department of Landscape Architecture, and in particular the Designed Ecology cluster—reflecting the importance of the interconnection with the University and its research. 

At the core of the scheme is a sequence of swales—shallow channels formed of engineered soils and porous aggregates that function both as water catchment and planting zones, allowing water to be treated, captured, and retained at source rather than relying on centralised infrastructure to take it away. Gravel at their rim filters out the worst of the pollution, and an overflow in the base connects to the nearby river Don. This green street reconnects the urban landscape with flows of water, nature, and wildlife. 

By creating a multi-purpose social, economic, and green/blue infrastructure, Grey to Green demonstrates the value of working beyond disciplinary silos in relation to shared goals,3susdrain, ‘Grey to Green Phase 1, Sheffield’ <> [accessed 21 February 2023]. as well as the opportunities of reversing the modern infrastructural imagination and seeing nature in cities not as a challenge but an opportunity. Instead of trying to fix the problem of drainage, its designers have built infrastructure around and with ecology. 


External links

Ruskin Square—a project by muf architecture/art and J&L Gibbons which combines blue/green infrastructure with inclusive social space via the creation of a new urban woodland 

susdrain—an online repository of information and practice relating to Sustainable Urban Drainage Systems