Friday 20 December 2019

River Isbourne works


River Isbourne works

            For a number of years, GWSR’s civil engineering department has been watching the River Isbourne as it passes under the railway to the east of Winchcombe Station. Over the years, it has meandered on either side of the large culvert through the embankment.  Although we call this a culvert, technically it is a bridge being a brick arch of 16ft span, 13ft high and 128ft long.
Upstream on the south side, it has been cutting into the embankment to the west of the culvert whereas downstream the bend of the river has been getting more acute and threatening our neighbour’s garden. In addition, the river has narrowed downstream as it has deposited silt on both sides. 

Earlier this year, David Symonds Associates were commissioned to prepare a report on the state of the river and its implications for the railway. The first part of this was a detailed survey on both sides of the railway including the depth of the water. This revealed that on the upstream side, the river had eroded so much ground that the stability of the carriage siding above was in doubt. In addition the neighbour downstream was getting increasingly anxious about losing his garden. Therefore David Symonds Associates were commissioned to prepare a scheme to safeguard the railway and our neighbours.

Upstream side with erosion on left and deposition on right of river.

Downstream side showing meander in front of neighbour’s fence.

            In an ideal world, the river would enter the culvert on a straight line and leave it on a straight line avoiding any bends that might lead to erosion. However that was not how the river was when the railway was built and it is not possible for such a course today without destroying our neighbour’s garden and possibly the back of his house! Accordingly the adopted plan is to return the river to its original course and strengthen the embankments to prevent meandering in the future. Designing such a scheme requires the cooperation and approval of a number of parties including Tewkesbury Borough Council as the river authority for the Isbourne. A wildlife survey was done which revealed that there were no bats in the culvert and whilst there might be crayfish in the river, this would not be an issue and the wildlife consultant would visit during the works to check. Unfortunately Himalayan Balsam was present on both sides of the railway. This is an invasive species and there are regulations for removing it which was done as an enabling works package by the contractor. Negotiations were also required with our neighbour, Winchcombe Reclamation, to the south east of the site to allow the contractor access. They have very kindly given permission for this access. After putting the scheme out to tender, Walsh Construction were awarded the contract and a start date agreed.

            All this process takes time with the result that instead of starting in late summer, it was late October before all the permissions and contracts were in place. The approved scheme utilises gabion baskets and mattresses, which are wire cages filled with pieces of hard rock. A membrane is placed behind and under the gabions to stop water eroding the soil underneath. Above the gabions the existing soil banks are being reinforced with a mesh membrane. Work started well with two large steel pipes being placed in the river on the downstream side to contain most of the flow and leave the sides as reasonably still water.

Flume pipes being installed with sandbag dams to encourage flow through pipes.

            This worked well for a time and then it rained. And rained. The river flow became too much for the flumes and Walsh went to Plan B: using sheet piles to isolate a section of the bank. The work resumed but then it really rained and the site was overwhelmed.


Sheet piles virtually submerged and our neighbour’s garden in peril.

Upstream the river was encroaching on the reclamation yard as well as the bank on our side.
At this stage, there was nothing to do but wait until the river level dropped and then seize each opportunity.

 
Completing the sheet piles on the NE corner

Once sheltered by the sheet piles, construction went well despite the very sticky clay and the interruptions of yet more rain.

Getting the stone cross the river.

Transferring the stone for the gabions became a game of pass the parcel with one excavator picking up the stone from the stockpile and handing it to the other excavator to place in the gabions. Watching from the top it was like a delicate ballet exercise! Perseverance paid off and the NE corner was completed.

NE corner complete apart from final landscaping.

Operations then moved to the NW side and the sheet piles were installed for this phase. This time excavation and construction was easier as there was no river in the way. Also the weather was a little kinder in that the rainfall was not as intense and the river level fell fairly quickly after each storm. By Christmas, the NW side was nearing completion as the site was secured for the holiday and the contractors took take a well-earned break after an extremely wet and muddy six weeks. Hopefully the weather will be better in the New Year

Work completed on the NE corner and underway on NW side.

Good progress on NW side and site secured for Christmas.

10 comments:

  1. can someone explain why we did not go in a straight line north and do away with the bends and use the flume pipes to take most of the water through .

    i presume that the gardens are also going to have sheet piling and gambion reinforcement to prevent erosion of their banks
    Merry Christmas john M.

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  2. I don't know whether this is the right place to raise this but I noticed from the train today that new fencing is being put in near Winchcombe. The contractor has pulled out and discarded the original GWR fence posts made of old broad gauge rail that I believe date back to the building of the line? Who authorized this vandalism?

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    Replies
    1. Where exactly was this?
      We need to keep the bridge rail posts, they are our only reliable boundary markers.

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    2. Frankly, I think the railway's boundaries are a mess. A comprehensive audit - and remedial action - is urgently needed.

      Property owners alongside the line have moved their fences onto railway land at several locations, essentially stealing railway property.

      At Bishop's Cleeve two householders have put gates in the railway fence, giving access to the lineside. One gate has been in place for years; the second gate was installed this summer.

      At Southam Lane a lineside landowner has been progressively extending their fences onto railway land for several years now, digging away the side of the embankment as they go - a dangerous thing in itself. We know how unstable the earthworks can be. They are now putting up buildings on railway land, as if it was their own property.

      I have no idea why the railway is content for this to go on. Not only does it damage the company's key asset - its property - but it places the GWSR in breach of its legal obligations, to ensure that the line is securely fenced throughout its length.

      A railway which allows anyone to shift fences, remove fences, tamper with earthworks, or place their own gates in the railway fence so they can stroll out onto the tracks as they please, is clearly not a secure or safe railway. If the Office of Rail & Road knew what was going on, they would be justified in closing the line down until the safety breaches were fixed.

      I genuinely can't understand why the official GWSR attitude to this seems to be 'Sit back - do nothing - let it happen'.

      I have a horrible feeling it'll take an accident - such as somebody walking onto the line through their illegal gate and being hit by a train - before anything is done.

      I wrote to the former PLC chairman about these concerns long ago, but never got a reply.

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    3. The GWSR is in the process of conducting an audit of the boundary fencing and have been taking action to rectify anomalies as and when they are identified. One of the key issues is that volunteer resources for this sort of activity are limited and with 15 miles of trackbed to look after getting on top of legacy issues will take time.

      Anyone with a tactful demeanour and an aptitude for or experience of this sort of work who has time to spare to volunteer would probably be welcomed by the department responsible. Volunteer application details can be found at:
      https://www.gwrt.org.uk/Volunteering.html

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  3. Jo, I put my comment on this on the Drain gang's site by mistake.
    Powli

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  4. Michael Johnson is quite right.
    Dealing with these encroachments "at the time" may be embarrassing but is relatively easy. Once left to become "formalised" it becomes more and more difficult to rectify, and restore the original boundaries. With potentially serious consequences.

    Powli Wilson

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  5. AM still awaiting a reply on my comment 21/12 which has baffled my Pway colleagues as we pass over the river at regular interviews .We are amazed that the scheme has not moved the direction of the river to the right so it goes straighter to miss the embankment facing the gardens of the house which must need protection.

    Are the GWR paying for all this work ? john M.

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    Replies
    1. John, you may not realise it but the works aren’t completed, the edge of the gardens parallel with the railway will be protected in a later phase of the works.

      As mentioned in the text of the blog, the river needs to stay aligned to the barrel of the culvert so this limits the amount of deviation from it's original course. As it also states, the design has been drawn up by specialists in this field, they may not be PWay specialist but they know about rivers and culverts :-) It has been approved by the relevant authorities controlling flood risks and riparian responsibilities, again as mentioned in the text. The work is essential if we want to save the end of the sidings at Winchcombe being washed out and the integrity of the embankment put at risk. The down side erosion is at a critical point where one big flood could do serious damage.

      Hope this answers your questions, Stuart, Lineside Drainage

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    2. many thanks , reassuring news for the homeowners and for our sidings above , although the track down to the river is now deep in mud and the adjacent siding may need reinforcement packing .

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