Slowing The Flow At Limb Brook: Sun 29th September 2024
Slowing the flow in the Limb Brook: on a damp grey week, we find out why working with nature is an answer to urban flooding.
Morning. A longer feature today, as I take a stroll in Lady Canning’s looking for fallen logs. There are plenty, and some have been dropped in a very particular way by a team of water engineers trying to watch and learn how nature does dampness. Those log engineers want to help prevent Sheffield flooding, and they need your help.
More on this below, along with a few seasonal suggestions to watch for, and a second chance for Secret Seating fans, who seem to have drawn a blank, so far, with last week’s mystery bench. We have a clue below, so let’s have your guesses.
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Damp Course
You may remember hiding from Storm Babet last October, as the extratropical cyclone hit Sheffield for several days, with flooding at Catcliffe and Endcliffe Park. As we hunkered down with our tea and biscuits, Roy Mosley of Sheffield & Rotherham Wildlife Trust grabbed his smartphone and headed onto the rain-lashed moors to make a TikTok video.
“I’m here up at Lady Canning’s plantation in an amber level warning storm,” chuckles the natural flood management influencer in his video, “and it’s fair to say there’s a fair bit of water around.” He moves on.
“We’re now at the SSSI bog,” he squelches, “and there’s no shortage of water here either.” He’s standing in the swirling waters of a site of special scientific interest, and appears to be sinking while he tries to explain the principles of woody dams and attenuation ponds.
He survived, and a few days later, Roy told me his experiences in the deluge (and the days later) left him to conclude that his team’s work in the Limb Valley may well have helped prevent flooding that weekend.
Last week, I headed back up to the Limb Brook with Roy and his swamp squad to bring you a natural flood management explainer. Think of it as a damp course for modern times.
Just above the start of the Lady Canning’s plantation, there’s a small unappealing path leading into what appears to be a bog. “This way,” says Roy, confidently followed by project partners Roger Nowell of Sheffield Council and Jackie Lowe and John McGlinchey of the Environment Agency.
We find the TikTok spot and stand reverently among the damp logs. “Last time there was more water here than anything else,” says Roy.
This is a woody dam, or spill dam, and is very simply a large log or two from one of the Lady Canning’s trees, dropped over one of the streams in the woods that form the headwaters of the Limb Brook.
Usually, the stream trickles underneath the logs, as it does today, but in a heavy rainfall event the log dam diverts a large proportion of that rainfall into hollows in the nearby woodland, where it has more room to sink into the ground or at least slow down as it heads downhill.
We ponder, and wonder if more logs could be placed differently. “You work with the land,” says Jackie Lowe. Nature-based solutions (as this is, to use the jargon) are bespoke for each location, she explains.
The work on the Limb Brook, funded mostly by the government’s Environment Agency, is what’s called a ‘demonstrator’ project, so is about learning what works, and acting as necessary. It’s not an exact science, Jackie explains, as we scramble through undergrowth to the large ‘attenuation’ ponds.
Placed strategically around Lady Canning’s, these ponds effectively collect all the water from the nearby moors that hasn’t already sunk into the ground, explains Sheffield Council’s natural drainage expert, Roger Nowell. So they slow the flow of rainwater from storm events, and while doing so provide a home for pond creatures, and the animals like birds and newts that might like to eat them. A flock of pond skaters dance on the water, and a dragonfly darts by.
It’s fairly quiet here today, but this pond is only yards away from one of the Cannings bridleways used by walkers, runners and mountain bikers, and their kids. A new path seems to have formed by the pond as people explore.
“It’s great for biodiversity, and for young people,” says Jackie. “We’re coming at all this from different angles, but we want the same thing.”
The whole plan seems idyllic. Drop a few old unwanted pine trees and build a few ponds, and we’ll have a wonderful wildlife site for families to marvel at the pond life, while also saving millions of pounds of expensive flood defence engineering work downstream. (Remember those plans from a few years ago, for a possible restructuring of Endcliffe Park to prevent Ecclesall Road from flooding?)
Jackie pauses and summons the cautious civil servant within. It’s about ‘layers of intervention,’ I learn. There’ll probably still need to be flood defence engineering, but landscape work in places like the Limb Valley will certainly help in flood events, and may even reduce the costs of engineering below. We’re still learning, everyone says.
There are more logged brooks in the woods near Whirlowbrook Park (where the local Friends group have helped out, as have the Friends of Ecclesall Woods lower down the valley).
Roy and Jackie show me one of the surprising citizen science successes of the project, which is effectively a pole with a bracket and signpost on top. This is one of several fixed point photography posts, where you’re invited to visit any of 15 specific locations around the valley to take a photo and send in to the project from your travels.
Dog walkers or ramblers who visit a route regularly are especially encouraged to help with their smartphones. Students of Sheffield Hallam University are helping SRWT evaluate the photos, which show how the various interventions are holding back water at particular times.
It’s particularly useful when its raining, says Roy, so if you fancy heading out for photos in heavy rainfall events, like him, the pictures you send in are a real help to measure the scheme’s benefits.
Heading down the valley, Roy agrees that felling trees to dam rivers is a job well suited to Eurasian Beavers, but he’s careful what he says about the ongoing feasibility study considering where to put Sheffield beavers when they eventually arrive here (probably).
It seems the delay is about waiting for the new government to decide whether beaver reintroductions must be fenced off, or not. Meanwhile, SRWT and partner agencies are drawing up a shortlist of possible beaver brooks. It’s possible the Limb Brook may have too many dogs roaming around, although it looks pretty suitable otherwise.
Whirlow Playing Fields is perhaps the most dramatic intervention on the Limb Brook scheme. Roger Nowell shows me the dividing line between a damp set of football fields at the top, still mown by the council, and a now unmown former set of boggy rugby fields below. The latter is now a series of ponds and meadows, with gentle pathways and occasional streams meandering around.
“One day I saw a snipe fly up from one of the swales,” says Roger, of a surprising wading bird normally found well away from people. “It was wonderful!.”
The project built several ponds here, along with swales, (a kind of shallow channel), leading between the ponds and eventually to the outlet into the Limb Brook down below. The ponds, and swales, variously fill up after heavy rain, but when it’s dry the channels are empty.
Meanwhile wildlife moves in, as wildlife loves ponds, meadows and occasional streams. People do too, and after consultations Roy says there have been no negative comments from the public about the changes here.
As we wander, admiring the moths and dragonflies, it seems the only troublesome issue is the desertification of some of the pond edges. Half the ponds were fenced off, to prevent excitable dogs bounding into the water. The fenced ponds have notably lusher vegetation, along with the birds and insects those plants bring in, says Roger. And apart from scouring out the plant life in some places, dogs with flea treatment can kill water insects if they take a dip, says a series of stern notice on the fence posts.
It’s about working with local people, says diplomatic Jackie Lowe. “Land use is nuanced,” she says. “It can be used for food, leisure, building, flood management, energy, housing, recreation.” All that has to be balanced carefully, she says.
You might just plant some thorny bushes to encourage dogs to stay away from three sides of a pond, says Roger. Still learning, you see.
As a finale, natural flood management influencer Roy explains how rainfall from the whole set of fields was once collected by a series of herringbone drains gushing into the brook below.
We navigate a particularly lush swathe of long grass to find a small black pipe. The whole site now drains into here, Roy tells me. And the last time it rained heavily, he came out to look (of course) and found a mere trickle.
Hours before Roy’s visit, the rainwater cascading onto Sheffield’s moors flooded into the swamps of Lady Canning’s, swirled around the dropped logs to slowly fill the attenuation ponds, gurgled around more log dams in the Limb Valley, and eventually found its way to the ponds and swales and meadows of Whirlow Playing Fields, where it kind of disappeared, leaving a swarm of wild creatures making their homes and livelihoods in its wake.
More of this kind of thing is needed to make a difference across the catchments of all Sheffield’s rivers, says Roger Nowell.
Roy ponders all this as we trudge back among the flowers and insects. The trial natural flood management scheme here in the Limb Valley seems to be working to slow the flow, and increase biodiversity, and make people happy, we agree.
“But it’s also about connecting people with the weather,” he says. “To see how the landscape changes.” The next time it rains, maybe you should get out there.
Autumn Watch
The Red Deer rut is just starting, so you have maybe four or five weeks to see (and hear) one of the city’s most surprising spectacles: scores of huge wild animals chasing each other around on the city’s borders. I’m working on a feature about the city’s deer with our friends at the Sheffield Tribune, coming soon.
And next Saturday is National Fungus Day: there’s a big event with Sorby Natural History Society at Shire Brook valley nature reserve, but watch out for more next month, as mushrooms and mushroom hunters will be popping up all over the place. I’ll try and keep track.
What’s On Out There (from Sunday 29th September)
A tiny selection from our regularly updated What’s On Out There in September news and listings post.
Sun 29th - Sounds of Summer concert at Whirlow Brook Park
Weds 2nd Oct - Longshaw Wednesday 5m social walk
Sat 5th - National Fungus Day with Sorby Fungus Group at Shire Brook Valley Nature Reserve
Sat 5th - Plant swap at Whirlow Brook Park
Sat 5th - Friends of Whirlow Brook Park Volunteer Session
Sun 6th - Sheffield Conservation Volunteers work day - Wadsley Common
Secret Seating (8 - second chance)
Was this too tricky last issue?! Maybe the mystery bench was too out of the way? Surely not - hundreds of folk pass within 50 yards every week. Just to help, here’s an archive photo of a dance group in rehearsal close by from a few years ago. Let’s have some guesses, even if you don’t know for sure. Answers in comments please!
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Great write up. That Jackie sounds like the kind of common sense civil servant that we need more of!
The Limb Valley scheme is great but it is a shame the Whirlow Pond wasn’t desilted as part of the scheme. It has potential to store a lot of water. It is also used for canoeing by local Scout groups but the silt makes this increasingly unviable/dangerous.
I wonder with some careful design and desilting if this pond could become an outdoor swimming and water sports venue and part of the slow the flow scheme. As far as I can tell there no outflows running into it and it could provide important health and environmental benefits.
Also we need to find a way to tackle the invasive skunk cabbage in the valley before it spreads to Ecclesall woods.