The hidden stream which became a vital part of city's flood defences

An underground stream, which had remained hidden for years, is now part of a brand new park and a key part of Sheffield's flood defences. Andrew Griffiths reports.

Dr Paul Gaskell, from the Wild Trout Trust, in Porter Brook pocket park. Picture Scott Merrylees.

‘Finning’, anglers call it. It is when a trout seems to hang motionless in the flow of a river, and I was leaning over a wall watching one do just that. Had it been looking back at me, it wouldn’t have seen a woodland tree canopy behind, which is the sort of place you might expect me to be when spotting wild fish, but instead the edge of a car park and behind that a nondescript building in Sheffield city centre.

I was in the award winning Pocket Park on the city’s Porter Brook, on the corner of Matilda and Sydney Street, and I was talking to Dr Paul Gaskell of the Wild Trout Trust. He was proudly surveying his handiwork and telling me about how they had created the river margins, which were now full of wild plants spilling over into the water.

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“This is a really steep proper Yorkshire spate stream,” says Gaskell. “And when it rains it comes tanking down through this section. It is quite difficult to anchor stuff in a smooth channel.”

The Porter Brook pocket park is in the heart of Sheffield. Picture by Scott Merrylees.

And that is the point of the pocket park - or rather, its two points. Its first is to serve as a part of the city’s flood defence strategy, to hold flood water when that rain does come “tanking down”. The second, in more benign conditions, is to provide a quiet place to sit, a bijou pocket of calm to escape for a few moments the pace of city life.

This capturing of the two sides of a river’s character in a single piece of urban design is becoming a trademark for the city of Sheffield. The first flood defence to double as a public space is on Nursery Street, and a third is planned at Castlegate.

What makes Porter Brook so remarkable, is that until recently this section had spent the last 150 years running underground through a pipe with an old woodyard on top. It was the nearby University Technical College that provided the impetus for the transformation - and the funding. When a project has multiple benefits, it also has multiple potential funding streams, and the pocket park was paid for from a combination of Environment Agency flood defence and city regeneration budgets.

But proof, it it were needed, that the creation of green spaces and havens for wildlife can bring real, tangible value to a city, the adjoining land is now set to be developed into private rented accommodation in a deal worth £38m. The private sector development will include commercial units and it is hoped that it will further expand Sheffield’s burgeoning cultural quarter.

The Porter Brook pocket park is in the heart of Sheffield. Picture by Scott Merrylees.

“Sheffield and other big cities are realising what an asset opening up these rivers and ‘renaturalising’ them can be,” both in terms of the environment, and of public health,” says Jan Stratford, who was the council’s development officer on the Porter Brook project. “We’ve tried to scoop the ground in this park, so you can actually get close to the water, which is quite unusual in a city centre, to be able to get so close to a river.”

The newly restored stretch of river may only amount to 80 metres on the plans, but the hope is that it will serve as a proof of concept and act as a catalyst to give other stretches of the river the same treatment. The plan is for the Pocket Park to be the first link of a chain which will run to the station, and allow the river to act as a green corridor around the city.

Sam Thorn is the city landscape architect who worked on the project. It was a chance meeting with Paul Gaskell of the Wild Trout Trust at a Yorkshire Artspace consultation event at the early design stages that led to the unique ‘renaturalising’ of the river in the park, rather than its “beautification”, as Thorn puts it, which would be the more usual landscaping approach.

“I gave my drawings to Paul and said this is what we’ve got at the moment, then he came back and said if you have the rocks positioned in these sorts of diamonds formations, then that is good for the functional aspects of the channel.” says Thorn.

So began Gaskell’s involvement. He swapped his more usual haunts of leafy riverbanks for a busy city centre construction site, where he was handed a structure built as an open sewer and asked to produce from it a desirable home for wildlife. It was a case of: ‘here’s the water, just add river’.

His approach is a pragmatic one.

“We look at what processes ought to be in a healthy river channel but are missing, and see what we can realistically reintroduce that is appropriate in the context of a small, upland tributary stream of a catchment like this.” says Gaskell.

Coir rolls stabilised the planting of margin plants, secured with netted rocks to withstand the floods. Boulders from the earth works were split and positioned in the river to create the kind of flows that nature produces over time when left to its own devices.

A few days later found me leaning over that same wall in the Pocket Park, again playing spot the trout, but this time with James Mead, Environment Agency Senior Flood Risk Advisor.

If the river has two natures, that capacity to wreak destruction when in flood, yet the potential beauty of its wildlife as a city backdrop, then that conflict is directly mirrored within the Environment Agency itself. The side devoted to flood control is all too often seen to be at loggerheads with the side which concentrates on the simple ecology of the river. There has been a recent example on Yorkshire’s River Aire.

But the devastating floods Sheffield suffered in 2007 explain a caution and heightened awareness of public concern.

“Any materials placed in the river - be they rocks or vegetation - can cause an increase in flood risk, so we’ve got to look to ensure we don’t increase that.” says Mead.

This can lead to problems with those concentrating on the ecology of a river, whose aim is to create a varied habitat for wildlife. But the Pocket Park on Porter Brook has been one occasion when the two sides have worked together to produce something rather special. Mead hopes that although small scale, this can provide a blueprint for further projects, and believes that the secret is to get all parties around a table and talking at the early planning stages.

The key seems to be sharing information.

There won’t always be direct flood risk benefits from these projects, so we might not always be able to bring funding to the table from a flood risk perspective,” says Mead. “But there may be other things we can do in terms of enabling access to our modelling, or enabling access to the information that we hold to allow the likes of the Wild Trout Trust to pick up on our flood risk modelling.”

Back in the pocket park, picnickers who looked carefully would have seen that trout rise to take a fly from the water surface, just beating the grey wagtail to it, that had been flitting from stone to carefully placed stone, along the brook’s length. While above, the hum of traffic and procession of city workers and students busied their way along the streets, who too were getting on with their day.