Progress restoration updates

Progress Wendover Arm

Good progress by Wendover Arm Trust on profiling / lining the channel, coping with a coal tar problem, and solving the mystery of the disappearing pipe

Grand Union Wendover Arm

August working party: Having now finished the brick work on the towpath side on the old swingbridge site at Bridge 4, “all we had to do” was to make a mirrored version on the offside. The existing structure condition was found to be very poor and most of the work done was demolishing the brick work and excavating down behind the bricks to give a clear working area. Rebuilding could now begin.

On to the main task of continuing the concrete pipe capping and roadway in the canal bed. [see explanation of ‘pipe capping’, right ...Ed] Excavation continued, following the “trench” infill that resulted from the pipeline being installed under the bed at the turn of the century. The concrete layer is 150mm thick and reinforced with steel “rebar” sheets. We have chosen to make it wider than strictly needed to just protect the Bentomat liner should the pipe ever collapse in future. This will allow the machines to run on a concrete “road” and thus avoid all the issues with mud churning and subsequent volunteer risks. It also allows the dumpers to run inside the wooden formers to get the concrete to where it is needed when casting the road.

This all went well until the line of the trench “disappeared”. We think the trench was originally dug by use of a steam shovel or similar, due to its regularity and depth. The clay pipe with mortar joints wouldn’t have lent itself to sharp bends so where did the pipe go? We also found that the old coal tar lining was intact across the canal bed, the coal tar having being put there long before the pipeline, as a final attempt to make the channel waterproof before the canal company gave up and piped the water.

Faced with this puzzle we went to the only place where we knew the pipeline would be and that was the next inspection pipe hole about 30m beyond.

We started excavating around hole and eventually found signs of the trench. Further digging back towards our work area showed that the trench soon disappeared. How could this be? Further delving was enough to find the top of the pipeline and we could now see which direction it was running. We also found that excavating with our 13-tonne machine was difficult due to the very hard (almost like limestone) chalk layers. It would seen the team 100 years ago found it so difficult to carve through, that they decide to tunnel under the rock! It must have been very risky to hand dig some 30 m under the rock, especially as what appeared to be a softer layer was more likely to drop from the roof... Mystery solved, the hole was filled in and it was back to the concreting. This con-

Pipe capping: an explanation The Wendover Arm was built primarily as a feeder to bring in water from springs near Wendover to feed the Tring summit of the canal’s main line – but it suffered from long-term leakage problems as a result of the porous chalky soil it passed through, and this led to its eventual demise as a navigation, and to the worst section being drained many years ago. That’s the length that’s now being restored: it has an 18-inch glazed clay pipe installed underneath, buried in the canal bed, to carry a feed to allow water from Wendover to still reach the pumping station at Tring (and from there to the Grand Union main line) after the canal had been drained. Due to the age of the pipe (which is now abandoned and blocked), as part of the channel restoration and waterproofing work, protective measures must be taken to avoid damage to the new lining system if the pipe ever collapses under the restored canal. Therefore the pipe is being uncovered, a section at a time, and a concrete ‘raft’ or capping is being installed on top of it to provide that protection. That capping also forms a temporary access road for machinery to get to and from the worksite, before the new channel is built on top of it, incorporating a waterproof Bentomat (bentonite clay matting) membrane to avoid the leakage problems recurring.

tinued as far as we could get in the time available, and we have now got to 452m from Bridge 4.

Meanwhile bed excavation continued on the next section ready for the following month’s concreting. A section of pipe was removed intact and will be kept as the only large section of pipeline to have been salvaged. It will become an exhibit at the old pumping station site at Whitehouses for everyone to see.

September working party: the The twoweek work party was largely blessed with good weather. It was so hot on some days that work stopped early to avoid sunburn and heat stroke! Our site layout once again allowed for volunteers to be well spaced apart for covid 19 infection avoidance.

On the bank excavation and channel lining: once we were sure that we had no badgers living in the offside bank at bridge 4, work progressed to rough excavation and then final profiling lining and block-laying on both banks. As can be seen in the picture, progress along the bank was pleasingly rapid. The towpath side, at 40m long, ended up being slightly more advanced than the offside. Bridge 4 can be seen in the distance.

Whilst we modify the “Bentomatic” (as we have christened the excavator mounted Bentomat handling rig that we have devised), we needed to find an interim method of handling the heavy Bentomat sheets. By adapting another handling tool, we

Pictures by WAT Guiding the dumper in, with the next load of concrete for the capping were able to cut 4m pieces from the roll on the bed, attach them to the lifting rig and place them on the bank with an excavator. Meanwhile the old swingbridge brickwork at Bridge 4 (as mentioned on the August working party report above) was cleaned up to remove the old crumbling lime, loose bricks, and other debris. The new ‘old style’ heritage bricks were carefully built up with fresh lime mortar. The coal tar solution: as alluded to earlier, a very long time ago the canal was Good progress in September with profiling, lining and blocking the banks

lined with a new-fangled material that was a by product of making ‘town gas’ (the predecessor of today’s natural gas) by heating coal in a closed retort. The residue from the gas-producing process contained many chemicals and compounds and one of the most useful was coal tar. This material was used on many of the roads of the day and is still there in lots of cases but covered with later layers of Bitumen (derived from crude oil). At the time this coal tar material was seen as a cheaper method to waterproof reservoirs and ponds compared to the traditional clay puddling process. The Canal directors decided that the leaky Wendover Arm should be coated with a layer of this material (it didn’t Bentomat handling, pending perfection of the Bentomatic ® work), and it is still there today.

In 2021 the coal tar is now a problem material when considering how to dispose of tonnes of spoil that now contains the tar. We have found that coal tar is not accepted at all at landfill sites, and that includes spoil with only small amounts of the tar in it. We know the tar does not leach into the subsoil and we also know that it is not easily dissolved in water, or it wouldn’t still be there after 100 years or so.

We have now been a lot more careful when excavating the banks. It has been possible to remove the contaminated top layers and the coal tar layer itself and leave the original clean subsoil exposed and then remove it and keep it separated from the tar-contaminated spoil. This in turn has allowed the removal of the “clean spoil”. (We will have a net excess of spoil, so something must be removed from site). This can be done relatively cheaply. Finally, due to the bank excavation and lining going well, it was decided to leave the concreting of the pipe capping until the last day of the fortnight to allow access for the machines and focus on the bank works. Another 30m of capping was completed on the last working day: the length now stands at 480m from bridge 4. Tony Bardwell Operations Director Rebuilding the second wall at the old swingbridge site by Bridge 4 Wendover Arm Trust page 31

Progress River Gipping

Next, our roundup of progress on restoration projects heads east for Suffolk and the River Gipping, also known as the Stowmarket Navigation

River Gipping

The River Gipping Trust have now taken delivery of all the timber components needed to build a wooden footbridge platform that will sit on 230 year old brick abutments and will cross the river Gipping in Suffolk. The 2m wide footbridge platform consists of five timber beams, each 10.5m long x 475mm deep x 200mm wide. The original timber footbridge platform was lost over 80 years ago and since then there has been no towpath along the river for around 1km.

The Trust have restored one of the bridge abutments and are working hard on the other before work starts on erecting the wooden platform over the river. Hopefully volunteers will start building the footbridge platform over the river in October and be able to re-open the 1km of towpath again.

The Trust hope to be able to undertake a 1km stretch of de-silting work just upstream of the footbridge improving the river conditions to enable canoes and kayaks to paddle more freely and have recently met up with the Environment Agency who in principle, subject to conditions, have indicated that they will approve our upcoming permit applications.

More photos and latest updates on our website https://www. rivergippingtrust.uk/ latest-news

Pictures by RGT The timber for the bridge deck is delivered... ...and delivered to the bridge site

Top: restoration of the first bridge abutment is complete. Above: the second bride abutment awaiting restoration hopefully to be complete during October. Right: once that’s done, the timber is ready for building the new deck

Progress Tennant and Mont

The Tennant Canal’s aqueduct is under threat, but there’s progress with funding a survey. Meanwhile on the Montgomery, channel work continues

Neath and Tennant Canals

There’s more positive news on the future of the Aberdulais Aqueduct, which was damaged by flood water 18 months ago leading to fears that it would collapse or be deolished - which would represent the loss of an important heritage structure as well as a blow to future reopening of the canals, which in recent years has been put forward as part of the wider Swansea Bay Inland Waterway scheme.

The aqueduct carries the Tennant Canal over the River Neath, close to its junction with the Neath Canal. The ten-arch stone structure is the second-longest in Wales (no prizes for working out which one is the longest!) but its low height and solid stone piers mean that it forms a barrier to water coming down the river during flood conditions. The canal here is unnavigable, the channel over the aqueduct has been empty for quite some years, and it has long suffered from flood damage and lack of maintenance. In early 2020 Storm Dennis caused further damage, washing away some stonework and causing a buildup of debris against the aqueduct resulting in local flooding and calls for the demolition of the structure.

The Neath and Tennant Canals Trust and the Inland Waterways Association have campaigned for its retention and restoration. They see the way forward as being a long term management plan and a heritage partnership agreement with the owners (the stillindependent Port Tennant Company which uses part of the canal as a water supply channel for industry) and public bodies (some of whom it was feared would support the removal of the aqueduct) including Welsh heritage organisation CADW, local authorities and Natural Resources Wales, to agree works to stabilise the structure. Fears of worsening storms and floods as a result of climate change mean that they see a need to act soon.

Following discussions with NRW, CADW, the Council, PTC and the Save the Tennant Canal group, IWA applied successfully for a CADW for a grant to cover the cost of a structural survey of the aqueduct, which will give an idea of the scale and cost of repairs needed. This survey has now been commissioned, and the results will determine the next stage in the campaign to save the aqueduct.

IWA

The main effort over the summer at Shropshire Union Canal Society’s worksite (rebuilding the length of the Montgomery Canal between Lloyds Animal Feeds near Pryces Bridge and Crickheath Wharf) has been construction of banks that require surcharge [Surcharge means pre-loading ground which is expected to suffer from settlement with weights, in this case stacks of large waterfilled plastic tanks of a type known as IBCs, so that the sinking occurs in a controlled way before the canal channel is restored], with the fourth and final one now finished. the bank in question is on the outside at the Lloyd’s Animal Feeds (LAF) end of the site. As a preliminary, the channel bed in this area had the works ground conditions on the site and had to be treated by the addition of copious quantities of grout and stone. Additonally, as part of this work, the corresponding towpath bank was reconstructed. In both cases the necessary stone was delivered to the banks by power barrow from the LAF compound and simultaneously by dumper from Crickheath. Although superficially similar the two banks had a very different construction. The offside ‘surcharge bank’ was held together by five layers of heavy-duty geogrid whilst the towpath is devoid of such technological wizardry.

The consulting engineers have now agreed that two banks at the oak tree, which were finished before Christmas, can now move from ‘primary’ to ‘secondary’ settlement. This means that the bulk of the likely settlement has now happened and accordingly the IBCs can be removed and the banks reduced in size to their final shape. Accordinly the IBCs were drained, moved (manually!) to the third and fourth ‘settlement’ banks and refilled with water. Also the bank reshaping work provides us with our own on-site quarry - no more imported stone required!

The other major task over the summer has been preparation for the start of lining / blocklaying of the channel. Part of these preparations is final shaping of the channel between the oak tree and Crickheath. This was a major effort mainly using hand tools. The nationwide shortage of building materials has made acquisition of the various lining materials a fraught process. However all of the necessary sheet materials and blocks are now on site and the start of lining / blocking work is imminent.

Incidently the grout mentioned above has a bit of history. It was originally obtained by the Canal & River Trust for scheduled winter work on the Toddbrook Reservoir at Whaley Bridge. However before it could be used there, the well-publicised failure of the spillway and the attendant dramatic evacuation of the town occurred. The subsequent emergency remedial work to the reservoir included much of the original scheduled work. Thus the grout was surplus to requirements and was diverted to the Montgomery. “An ill wind...” if there ever was one!

See also Monty camp report on page 10