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Montgomery Canal Restoration Review 2012

 

In one important respect – our Great British Weather - the 2012 restoration season was a mirror image of its immediate predecessor. The 2011 restoration effort started off bogged down in saturated ground and then, from May onwards, benefited from the dry conditions which, of course, turned into a prolonged period of drought. Although it is hard to remember now given the ‘summer’ that we have endured, at the start of 2012 the country was still drought affected with water rationing was very much on the cards. Alas from May this year the rains returned with a vengeance with serious consequences for the restoration works. But before we get to that, the story of a pleasant lunch......

In November 2011 we had a visit from a number of British Waterways engineering staff, led by Les Clarke, who came to look at current progress and future challenges. At that time the first ‘production runs’ of lining had been made adjacent to Pryces Bridge. This section used a bentonite liner covered with geotextile, and an overburden of dense concrete blocks laid on end. This produced a high quality finished product but the large number of operations meant that it was very labour intensive and time consuming. During the walk along the towpath that day Les mentioned that he had been approached by a representative of a company offering a new type of lining material that potentially replaced both the bentonite and the geotextile, and required only minimal overburden. The significance of this was immediately appreciated by the Society members present. Les was questioned – ‘interrogated’ would be nearer the truth - about this new product over lunch. It became apparent that the material offered the possibility of much quicker progress on lining for far less effort. This was something worthy of further investigation!

The ‘new’ lining material was essentially a version of the black non-woven geotextile we used previously but factory-treated with an acrylic waterproofing chemical. On contact with water the acrylic reacts and swells to form a stable waterproof gel that is self-healing when punctured. Its other property is that it does not actually need covering to work. However some form of protection is required to protect it from damage in a working canal. In our case the existing blocks could be used, but laid on their side rather than their long edge. Since all the work of cutting, transporting, and sealing the bentonite was eliminated, and the blocks were laid side-on rather than end-on, this promised much quicker progress than hitherto. Thus the Society became the launch customer for this new material. The news soon spread and we have had visits for a number of canal societies over the year to view it and share our experience. The downside of being the first customer is that the production process for the material was not well established and Mike’s diplomatic skills were tested to the full to ensure a supply – albeit in a variety of sizes and colours – through the year.

Anyway, back to the weather and why it matters. The main tasks through the year involved creating two accurately shaped slopes each of 22 degrees gradient – one about three metres long on the offside and a smaller version on the towpath side – to provide the profile of the finished channel. These slopes and the channel bottom are then lined. Shaping operations are nigh impossible in wet conditions since it is difficult to stand safely on the slopes. Similarly the lining material becomes very slippery when wet. Thus wet weather is bad news for progress. As the rain continued through the course of the year, and the ground became steadily more saturated, the list of ‘main’ tasks had to be augmented by another, namely, pumping, From June onwards the ‘weekend’ came to include Friday as well which was spent pumping out the sumps, usually with a variety of hired equipment. Without this most of Saturday's working time would have been lost. During a number of work parties the pumping operations were repeated on Saturday and Sunday as well, requiring the more or less full time efforts of a couple of volunteers.

The shaping operations commenced in March at the Redwith end of the length. This section was the most difficult encountered to date for a number of reasons. The final configuration of the channel in this area was a funnel shape reducing to the bridge-hole, and this required a mixture of accurate setting out and inspired guesswork to get right. The ground conditions were the worst encountered on the whole length, and that is saying something! There was a bewildering variety of soil types, a huge quantity of stone and bricks (presumably from the former coal wharf and bridge), together with enough coal to fire a small power station. Also the narrow channel meant that much of the work was done by hand. However the combined might of a rotating bucket digger, picks, spades and mattocks ensured that progress was good. The spoil was used to build up the offside bank in the area of the culvert with the result that this section now began to resemble a canal again.

Some 70 metres at the Redwith end were shaped down to final level by the end of May - this being half way from the bridge to the compound. From here onwards things began to go wrong. We took a calculated risk of not installing a French drain on this section, thinking that a few sumps would suffice. This was because this section was historically free draining since the adjacent fields were below the level of the base of the channel. This gamble failed as was soon demonstrated when shaping gave way to lining on the section. The dumpers loaded with blocks reduced the level base of the channel to a mud bath and this got worse with each succeeding wet month. In the end a small section of French drain was installed and the bottom of the channel re-excavated to a slightly lower level to get rid of the mud immediately prior to lining. Oh for the weather of 2011!

The lining gang also suffered in the mud. Having started the year at the Pryces end they switched to the Redwith in July. In theory the new liner, unlike benonite, could be laid in wet conditions but this did little to aid the cause. Their main problem was, of course, how to transport the blocks without churning up the channel base. They tried everything - duckboards, cement and layers of dry material to absorb water, constant pumping. They were prepared to work in appalling conditions for much of the year but even so operations had to be abandoned on a couple of weekends. It is a great tribute to their tenacity that 144 metres of channel was lined during the course of the year. The lining gang’s final operation was placing the stone rip-rap on the top of the offside slope at the Pryces end. This will eventually act to absorb wash and be a home for aquatic plants. One is tempted to add that this section just requires water and it is finished. However, in the light of events this year, maybe not!

How much production was lost by the effects of the bad weather this year? Maybe cumulatively a couple of weekends – say 40 metres of finished channel. Whether this matters in the great scheme of things remains to be seen.....

So, a year which started with us working with British Waterways and ended with us working with the Canal and River Trust has had its highs and lows (or should it be wets and drys). What can be said is that, as always, we have had a lot of fun doing the work and we look forward with anticipation to 2013.

David Carter

 

Footnotes:

At the end of the year the lining extended 82 m from Pryces Bridge and 92 m from Redwith Bridge, leaving 245 m to do.

For the UK, 2012 was the second wettest with 15% more rainfall than average (records dating back to 1910).
For England, 2012 was the wettest ever with almost a third more rain than normal.

For Shropshire, 2012 was the wettest on record, rainfall was 142% of the average (records for RAF Shawbury, 1946 to date).
The first quarter saw only 56% of the average, the last 3 quarters combined saw 166% of the average. The 7 months from April to October inclusive, which directly affected our May to November work parties, saw 646 mm, 9% more than the previous record and 163% of the average for the period. April, July and December each had more than twice the average, December the highest ever.

 

photo 1 448 photo 4 448
Rainfall for November and December combined was 176% of the average. These pictures show the result on December 25th.
R0011298c 448 R0011336 448
Problem? What problem? Some people should get out more
(B)rogues gallery
MF RH
PJ FB
AVM JM
If you can name the owners of all these feet, you could be going on an all expense spared weekend in rural West Shropshire.
November 2012
2011 Review
February 2013
2013 Review

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