Weir repairs complete after two setbacks
VOLUNTEERS from the Friends of Cromford Canal have completed repairs to the weir at Pinxton Wharf following delays caused by heavy rain and the first coronavirus lockdown.
They undertook the work in response to concerns by Derbyshire County Council at the downstream state of the weir on the arm of the Cromford Canal known as the Pinxton Arm.
As well as trouble maintaining the water level in the wharf area, which is now a fishery, the council was also concerned at the possible collapse of the weir due to scour in times of heavy water flow and vandalism over the years.
The Friends’ engineers convinced the council that their volunteers could do a more than adequate repair at much less cost by increasing the weight of the downstream side by casting a concrete apron that the canal water would flow down.
Work couldn’t be carried out as planned in 2019 due to heavy rain during the autumn and then in March of this year the planned start was put off by the Covid-19 lockdown.
The weir was originally constructed of wire gabions filled with stone along the side of the track by the canal and possibly forming the core of the weir. The upstream side was some form of plastic sheet and clay to prevent passage of water through the stone-filled gabions; the downstream slope was stone riff-raff with a crest of concrete kerbs set in concrete.
In 2019 FCC had been planning a Waterway Recovery Group work camp led by WRG North West but with the restrictions on volunteers staying overnight a work camp was out of the question. The engineers arranged a new work programme and method statement for FCC work parties which was approved by DCC which agreed to pay the cost of materials and plant hire.
In August preliminary work started to remove vegetation and clean off the old stones. It was decided that the weather looked promising and work started in the second week in September. Plant and some materials were supplied by the Erewash Canal Preservation & Development Association and Waterway Recovery Group from Langley Mill; concrete blocks and aggregate were brought in ready.
The FCC work party led by John Barker pressure washed the existing stone and cut the offside tail of the weir back into the bank.
About 30m towards the wharf above the weir, there was a construction of a temporary dam with polythene sheet and 150 sandbags; subsequently pumping out of this dam and around the weir reduced the level at the weir crest by about 250mm, just what was needed.
Below the tail of the weir there was a layer of small stones and on these were laid a row of concrete blocks, about 2.5m from the crest of the weir to form the bottom edge of the new concrete tail. Along the offside edge were laid a row of concrete kerbs set in concrete to finish about 100mm above the finished concrete.
On the towpath side the original row of stonefilled wire gabions was deteriorating, this was shuttered and concreted to about 100mm above the weir crest. This also filled in some holes in the gabions near to the weir crest where water was escaping through the stone gabions.
A shutter board was set up to give about 100mm of concrete over the row of concrete blocks and with a board between the crest of the weir and the bottom shutter, the stones were levelled off by the addition of more stones to give a finished concrete cover of about 150mm. When the concrete was laid, a sheet of steel reinforcing fabric was incorporated in the concrete.
Over the next week the shuttering steel supports were removed, the concrete kerbs forming the crest were pointed up and the wooden fence was repaired and the temporary dam removed. The total direct volunteer effort on site was over 360 hours plus 71 hours’ travel to and from site.
During the work Mick Bacon, whose land is adjacent to the weir, was a great help in storing materials and tools in his yard and he frequently came round to give advice and encouragement. All work was done under the FCC Covid-19 risk assessment with social distancing.