Cherry Hinton Brook repair work shows value of protecting chalk streams

The repair of the Cherry Hinton chalk stream, one of 80 council biodiversity projects under way in and around the city, has had its fair share of challenges.

Those involved in the project include Friends of Cherry Hinton, Abbey People (for the Coldhams chalk stream off Barnwell Road), The Wildlife Trust, Cambridge City Council, and Cambridge Water (whose grants aid the work).

“We’re trying to create a varied habitat in different conditions, so it self-regulates,” said Vic Smith of Cambridge City Council as she prepared hazel sticks to be used as a ‘fence’ to protecting the banks. “A natural stream would meander, but the Cherry Hinton chalk stream has been canalised. It’s different at Coldhams Brook: there we felled the trees on the banks – they’re still living – and hinged them to the banks, then back-filled it with brushwood.”

Ruth Hawksley, The Wildlife Trust wildlife officer who overseeing the improvements at Cherry Hinton Brook, said: “We were using hazel faggots – or fascines if you prefer that word – which are just bundles of hazel branches tied tightly. They were made by volunteers at Hardwick Wood as part of the coppice work there – they use a ‘faggot engine’ which is basically a frame allowing you to compress the bundle very tightly. We used them to change the shape of the bank to narrow the channel, so on Tuesday we backfilled the shape with earth as you can see from the photo.

“It looks quite raw now but will look better once the vegetation has recovered. We’ve increased the habitat diversity in the brook by introducing areas of fast and slow, shallow and deeper water and what we hope will remain as some clean gravel, which some invertebrates and fish require. We’ve also increased the sinuosity of the brook by emphasising the shape of a bend that was already there.”

Unfortunately volunteers and environmental teams faced additional difficulties on Monday at Cherry Hinton Brook as they continued the repair work along the chalk stream’s banks. The chalk stream sits next to a nearby allotment, whose gardeners are permitted to pump 4,000 gallons per person per day from the ‘protected’ chalk stream without a licence.

“There is a danger they will drain the brook which is quite annoying,” said a spokesperson for Friends of Cherry Hinton Brook at the site. “There’s three of them using pumps but they pump quite a lot and sell it to other allotment holders and people who live round here are upset.”

However Paul Holmes, secretary of Blacklands Allotments Association, said the water extraction is minimal.

“You wouldn’t notice it was gone,” he said. “They don’t take that much. We’re happy with how it is and want to be left alone to get on with it.”

Mayor Mark Ashton, a Cherry Hinton councillor for 12 years, said: “We’re well aware of the privilege of having a chalk stream. They [the volunteers and council] are trying to restore it to its former glory.”

Cllr Russ McPherson (Cherry Hinton, Labour) added: “I’m a great believer in education to get the message across about the brook and water: I had to do a lot of research to understand how important it is.”

A spokesperson for Peterhouse, which owns the allotment land, said: “Blacklands Allotments Association lease the land from Peterhouse and operate within the terms of their lease. They have always proven to be a responsible group of people who know the allowances regarding the use of water out of the brook.”

An Environment Agency spokesperson said: “The maximum volume of water that could be abstracted without a licence is 20 cubic metres per day. We have not received reports of allotment holders taking more than this allowed amount at Cherry Hinton stream. We ask anyone with concerns about water abstraction to report it to our 24-hour incident hotline on 0800 807060.”

Another issue is that the site is popular with young adults who damage the brook trying to access the nearby lake.

“They fill up the brook with wooden planks from the allotments – and shed doors, compost bins and fences,” said a volunteer with Friends of Cherry Hinton Brook. “They drink and take drugs. They leave behind huge canisters of nitrous oxide and behave very stupidly. It used to be locals and now they come from all over East Anglia using social media.”

“They’ve brought in angle grinders to cut the steel fence, that’s how determined they are,” added Cllr McPherson. “And inflatable bridges.”

Cambridgeshire Police said: “We encourage everyone to report crimes to us as promptly as they can. If it’s an emergency or a crime is in progress please call 999.”

Meanwhile, Cllr McPherson’s comment about education may be the best way forward: there is confusion about the work being carried out here – not helped by South Cambs MP Anthony Browne calling it ‘greenwashing’ – because although people are rightly concerned about water and the unique network of chalk streams which is central to Cambridge’s survival, the key to their future wellbeing is understanding what their optimal state is, particularly how much water should be flowing through the brook – and whether it once featured trout.

Ruth Hawksley said of the trout suggestion: “It’s true that there used to be more water in the brook – I don’t know exactly how much but it’s believable it could once have carried trout. One reason we were doing the work on Monday is that the channel is too big for the amount of water flowing in it, for two reasons: the amount of water is less than there probably was in the past due to abstraction reducing the amount available in the aquifer, and secondly the channel has been widened and deepened for drainage. This makes the flow very slow and the bed of the brook uniformly silty. The brook then can’t support the ecosystem that’s needed for a healthy river and clean water. We are aiming to make some areas where the water can flow faster and keep some gravel clean – it takes some energy to move the silt within the channel. What we can’t easily do is increase the flow of water in the brook, which would be a huge benefit.

“In the case of the Cherry Hinton Brook, there is currently no connection to the main river for fish, so no opportunities for trout to move upstream into it and it’s unlikely anything we do there will allow trout to arrive by themselves unless that connection is fixed.

“We didn’t finish putting all the gravel in on Tuesday as we found a moorhen nest and left an exclusion zone, but we’ll be back later in the year to add the rest.”