Grantham Canal, Cotgrave Update
By John Nuttall, Regional Project Manager, British Waterways
Background to the Project
The Grantham Canal Environmental Project at Cotgrave is part of an Single Regeneration Budget / Rechar (Coalfields Regeneration) project to provide improvements to the Grantham Canal and to compliment a major colliery reclamation project to form a country park adjoining the canal.
The project, which commenced in February 1998, is funded over 5-years and the majority of the works being undertaken on the canal are due to be completed by March 2001 with a budget of £613k over the whole lifetime of the scheme.
Those with an interest in the Grantham Canal will recall that over several years there have been various studies undertaken to establish the feasibility of restoring the Grantham Canal. At the same time a Grantham strategy has been prepared, which recognises opportunities for other leisure uses over the whole length of the canal until such time as restoration can become a reality. The Cotgrave scheme is a good example of a recreation project linking to the country park, but which maintains the integrity of the canal at the same time as preventing the continued decline which has occurred in the almost 70 years since closure.
The Cotgrave Site
The overall site is 2.2km in length and has suffered from mining subsidence. This could easily be recognised in that lock no.6 had large concrete cappings over the original lock copings, which were remedial works to compensate for the earlier subsidence and raised the lock walls by almost 5OOmm.
The scheme commenced with bank protection measures to renew and provide waterway approach walls above and below the locks, which would also act as moorings for craft waiting to use the lock. Boreholes taken from the design work downstream of lock 7 established substantial piles were required at that location due to poor quality of soil conditions or possibly of fill used to overcome the mining subsidence.
When the waterway walls were being constructed the opportunity was taken to de-water locks no.6 & 7 which had probably not been fully inspected since the canal’s closure in the mid-1930’s. Those familiar with the canal will be aware that at lock 7 there was a very substantial cascade constructed of concrete from the period when the headgates had been removed. At lock 6, presumably because of subsidence, the cascade was not as substantial a structure construction having less fall.
The inspection of lock 6 established that the lock had stood up remarkably well to the subsidence. The walls were generally in good condition, but there were substantial areas where facing bricks required removal and the remains of timbers from former wooden hollow quoins have deteriorated to an extent where total renewal was the only option.
The upper and lower lock approach walls were in a badly deteriorated condition and close to collapse when the concrete dams were removed. The lock floor (lock 6) required almost no remedial works.
Lock 7 – Who Swiped the Lock Floor?
At lock 7 the story was very different. When the lock chamber was de-watered there was found to be no lock floor whatsoever, only the remains of a timber frame with substantial amounts of loose brickwork lying around the base of the lock walls and in the lower approach.
Restored Lock 7 – May 2000
Unfortunately to date I have not had the opportunity to undertake research to find out the history behind this peculiarity. Sufficient to say that our investigations revealed that the lock walls themselves have remained in good vertical alignment presumably as the buttress units to the rear of the walls are founded on good ground. At the low end of lock 7 we found the remains of a former swing bridge base, but no parts of the original bridge. The bases have been rebuilt as part of the works. A concrete floor was built into lock no.7 prior to commencement of the lock refurbishment.
Phase Two – Improving the Environment
The second phase of the works in late 1998 and early 1999 was to dredge the channel of the canal and place the material to the colliery site for use as subsoil, forming part of the colliery landscape works. The canal is quite rich in environmental and ecological terms and careful monitoring was required to prevent disturbance to voles etc. I am pleased to say that some 12 months after the dredging, the environment has seemingly totally recovered. The water space shows considerable improvement in presentation following the dredging and was even more attractive when water levels were raised.
To ensure that the site traffic could access the locks for the rebuilding works, 3m wide access roads were built into the site from Cotgrave Road and Hollygate Lane. The access track works, which were substantially undertaken in winter conditions were also required to minimalise the danger of the towpath collapsing from use by site traffic and cranes to lift in the lock gates. Between lock 6 & 7 a 2m wide canal towpath construction was placed, as this area was not required for site plant access.
Restoring the Lock Chambers
Lock 6 & 7 were rebuilt between September 1999 and April 2000 and as much of the original fabric as possible has been retained. By careful resourcing we were able to re-use the recovered copings to surface one side of both locks only importing replacement material for the offside of the locks. I am pleased to say that the concrete used to raise the walls on lock 6 was successfully separated from the copings and that the less substantial concrete dams have not blocked the ground paddle inlet chambers and the culverts which discharge into lock 6.
At lock 7 however, the concrete placed to from the cascade has not had any shuttering or other protection in the area of the ground paddle chambers resulting in blockage within the chamber inlet and lock gate paddles had to be used to avoid unnecessary demolition at the lock chamber. In the long term we will need to consult with specialist contractors to find a way of breaking out the concrete in the chamber inlet to reinstate re ground paddles without unnecessary lock wall demolition. New lock gates (constructed in ekki timber) had been fitted to both locks and an arched ekki accommodation bridge has been installed at lock no.7. This bridge provides a pedestrian access to link the canal and the Country Park. There is provision for the bridge’s removal in future (if required) and for fitting footboards to the lock gates if the bridge obstructs navigation.
The Opening Ceremony
The locks were opened on 23rd May 2000 after an overall construction period of approximately 26 weeks. The ceremony for the lock openings was very well attended with representatives present from British Waterways, Nottinghamshire County Council, Rushcliffe Borough Council, Cotgrave Parish Council, South Kesteven District Council, Melton Borough Council and Leicestershire County Council in attendance in addition to the Grantham Navigation Association, the Grantham Canal Restoration Society and the funding providers.
Opening ceremony, Lock 6 – 23rd May 2000
To Finish the Project
We are now at around mid point in our overall programme. The works, which remain include provision of fishing platforms, conversion of the access roads into a towpath suitable for recreational use including cycling and for access improvements at the site entrance points. It is hoped as part of the environmental and landscape works to undertake hedge planting and provide suitable rest benches along with information panels/interpretation signs. There are several culverts beneath the canal which take surface water from the colliery site into the Polsar Brook feeder system and these will be surveyed.