Connectivity at Coniston Cold

And so it comes to pass….Coniston Cold weir, which in various forms has been a man-made obstruction to fish passage on the R Aire in N Yorkshire for the past 180 years at least, is no more. Instead, there is now 20.4km of uninterrupted free passage along the Aire and a major tributary.... and all for less than £8k!

Coniston Cold Weir: 19m wide and 1.2m headloss, with a 4m horizontal block-stone apron

I will not reinvent the wheel and spend time here discussing how weirs cause environmental issues. The evidence is abundant and simple to find in the scientific literature, and my colleague Paul Gaskell has recently summarised much of that, here. Then there are global-local events like World Fish Migration Day to raise awareness and I would wager that almost every conservation body involved with river restoration has a hit-list of target weirs on their local patch.

Aire Rivers Trust has been floating the idea of removal of this structure for at least 6 years, as elsewhere in the catchment it is developing a head of steam to tackle the last four significant barriers on the mainstem Aire (via HLF funding in partnership with the EA – Developing the Natural Aire, or DNAire for short). Since arriving in Yorkshire, I’ve been (quite literally) chipping away at many of the smaller but no less significant barriers on several tributaries like Harden Beck in partnership with Aire RT and the EA.

Coniston Cold without the weir, awaiting some spate flow to naturally rearrange all the loosened cobble and gravel

So, how does a project like this finally get off the ground? Kevin Sunderland, Aire RT’s weir guru sent an email to Pete Turner (EA Fisheries Officer) and I because he had finally made headway with the charitable trust that now manages the site. The powers that be could see the environmental benefits to removal and the tenant farmer was also supportive. We met, in a pub, of course.

We thrashed through all the possible scenarios and divvied up the workload. Were there any services associated with the structure, abstraction licences, or potential impacts upon other structures resulting from our plans? Was the weir listed or of cultural significance? How would the river bed be affected, for what distance, and in which direction? What monitoring could we put into place?

With Kevin keeping the landowner liaison up to speed and confirming any requirements from the Council’s Archaeological Unit, Pete set about contacting other components within the EA, notably Claire Bithell in Geomorphology because we needed a full topographioc survey, and finding the relevant people to speak to regarding a service search and abstraction licensing. My job was to manage the project overall, coordinate site visits, assess the integrity of the structure and develop a strategy for the removal with the contractor, as well as draw up all the requirements for a Bespoke Permit from the EA (Risk Assessment, Method Statement etc etc). The latter included specifics on sediment management, any fines arising from the work or resuspended, and so I contacted Hy-Tex Ltd and ordered biodegradable Sedimats to trap those.

Dr Jeoren Tummers & colleague (Durham University) electrofishing below the weir

As a part of the Adaptive Management of Barriers in European Rivers (AMBER) project, Durham University staff were keen to survey the fish population (in terms of species composition and density) both prior to removal and after the river had re-naturalised. The pre-works data suggest that while all species were found both above and below the weir, the numbers and size distribution were very different. I hope that they will provide the details in a separate blog contribution when they have conducted the post-works surveying.

With uncharacteristically dry weather extending to 10 weeks, we were desperate to get a move on! In preparative steps, I removed the three boards in the weir crest notch which focussed all the flow and dried out the remainder of the crest and majority of the apron below. Once we had the bespoke permit in place, we also made some exploratory cuts with a Stihl saw to ascertain whether any metalwork was within the structure; thankfully, not. Diaries were consulted, and D-day was set for the 18th June.

Sedimats in place and the 8-tonne machine on approach....

First steps were to set-up the time-lapse camera, prepare the plant entry point, remove one low branch that would cause hassle for the operator, and install the Sedimats. Then it was a case of shifting some stonework from the apron to create a ramp for the 8-tonne machine to get onto the apron itself, from where work could commence. A pecker was used to demolish the crest material into manageable chunks which could be relocated using a bucket. As the site is on a manufactured bend in the river, the EA Geomorphology team were confident that a point bar would develop on the inside bank (left bank) and hence much of the material arising from the demolition was used to infill the weir scour and top-dressed with formerly trapped cobbles. There did turn out to be a little bit of metalwork, so much of my time was spent scouring and scavenging for pins and small sections of mesh. They say a picture paints a thousand words. The time-lapse video tells the tale of ~36hours in roughly 3 minutes….

Time-lapse of Coniston Cold Weir removal

To summarise the project timeline:

  • The weir was in place for at least 180 years
  • Occasional discussions between the Aire RT and the owner continued for ~6 years
  • Planning the details from receiving a verbal owner agreement = 5 months
  • Bespoke Permit application turnaround = 2 months
  • Removal of weir = 2 days
  • Time to observe a benefit = 4 hours after starting removal, a mighty minnow migration

 

 
Minnows migrating through the extended weir notch and ramp under creation, ~4h after starting work

Our work has reconnected 20.4km of river and becks...for the princely sum of just under £8k! 

The actual site is still effectively a rock ramp with an artifically steep, though passable, gradient. Now we have to sit and wait and let nature take its course (as it should) through the loosened cobbles and gravels. As I write this, we’ve had a further 4 weeks of zero rainfall, and so the site looks essentially the same as when we left it. The time-lapse is still in position to await the arrival of some spate flow and record what occurs. In addition, I have set-up a motion activated camera to capture some of the wildlife using the site. So far, it has mostly caught adult and juvenile crows working over the new sediment bar and squabbling over invasive crayfish!

 

'Wildlife' caught on camera: juvenile crows squabbling over an invasive signal crayfish

I’ll update on the channel development and any other findings in due course. In the meantime, if you have any specific questions, please do not hesitate to contact me.