Restoration & Problem Solving
The restoration of Wallbridge Lower Lock by teams of volunteers is proceeding well despite the failure of the stop plank dam which created the collapse of the canal channel.
It was all going so well…
Jon Pontefract explains,“The Lock chamber was cleared out by Land and Water Services. The SDC Volunteers, working on Tuesdays and Thursdays, created a dam below the lock using aggregate bags filled with the spoil removed from the chamber. The bags hold a tonne or so of material. The crane being used on the construction of the McCarthy & Stone complex above the lock helped us immensely. We were very grateful for the crane driver’s skills in creating the dam from such a height above the lock.
"The lock chamber was pumped out and scaffold erected on both sides in the chamber. Then, six weeks of Waterway Recovery Group (WRG/wrgie) Camps got things off to a cracking start. They removed the coping stones from both sides of the lock chamber in readiness for the brick laying".
'In the groove' — historically speaking
Some interesting rope grooves were found along the edge of a number of lock chamber coping stones on the warehouse side of the lock. These grooves suggest that cargo may well have been lifted from and lowered into vessels within the lock.
Peeling back the coping stones revealed a 225 year old lock chamber in amazingly good condition.
Just seven courses of defective brickwork on each side of the chamber will need to be replaced.
Ground paddle chambers at the top end of the lock, filled in with blockwork during river channel works in the 1960's, have been opened up and again found to be in surprisingly good condition.
Every problem has a solution
A problem occurred overnight on 18th / 19th August when the concrete beam supporting the upper stop planks was undermined by water pressure and poor canal bed integrity.
This caused the rapid loss of water from the channel above the lock. The swift passage of water under the concrete beam and then through the lock chamber caused the collapse of the wooden piled edge of the channel and towpath east of the lock.
The Stroud District Council Canal Restoration team led by Dave Marshall were quick to identify the solution.
Dave explains, “Advice and guidance given by The Environment Agency and the Civil Engineers we consulted has resulted in a clear and achievable plan. First we must reinstate the stop plank dam on a firm concrete base. That will be created behind a line of interlinked piling known as Trench Sheeting. Then a 2metre by 5metre raft of concrete some 200millimeters thick will be poured to form a firm and sturdy base at the lock entrance. When that is all set the stop planks will be reinstated and the channel will fill with water from Slad Brook.
"That water will hopefully be flowing through the by-wash / fish pass at the beginning of October. The channel east of the lock will be temporarily re-profiled with a battered, or sloping, edge where the revetment has failed. Volunteers are also reducing the load on the remaining revetment by taking away material. Fish spawning regulations mean that we are unable to implement a permanent solution until May. That gives us a few months to decide, but it is likely to involve diverting the cable (which lies under the tow path) and battering back the slope."
Solution applied in the sunshine
The London branch of the Waterway Recovery Group volunteers swung into action over the sunny weekend of 12th/13th September to implement the piling solution.
The first two photos show eleven lengths of trench piling being driven into place.
WRG Team Leader Pete Fleming commented, “We were very pleased to be asked back.
"We have been down a number of times this year. We always receive a warm welcome as well as warm & dry accommodation.
"This team has some piling experience and the piling job should be completed this weekend. I hope so anyway as I have to be back in my office on Monday morning."
When asked the ‘where & what’ question Pete replied with a grin, “I am a civil engineer with Network Rail based in Peterborough actually”.
Whilst the piling team were hard at work in the sunshine, fifteen more wrgies, pictured above right, were busy with the bricklaying in the lock chamber.
SDC’s Jon Pontefract adds… “Volunteers will be working on the lock every Tuesday and Thursday. Whilst there is no public access to the site the site can be viewed on the Lower Lock Webcam on the Cotswold Canals Trust website."
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