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An Informative Afternoon in Manchester

Organisers of local meetings with a visiting speaker may worry about whether anyone will turn up on the day. That was not a problem for the L&B North West group meeting on Saturday 17 February 2018 – the small (and rather warm) meeting room in central Manchester was full to bursting point to hear Chris Duffell’s talk "Designing the Line - Turning our dreams into reality".

Bob introduces Chris Duffell (far right). No-one seems to have taken a picture when Chris was actually speaking. Photo: Peter Ainley

Chris gave us a fascinating insight into the work of the L&B’s Construction Design team, a group of five experienced Civil and Structural Engineers who are developing detailed engineering designs so that, as permission is granted, funding can be put in place and work can commence on the ground.

Chris began by describing the painstaking work needed to understand the construction of the surviving railway formation and structures. This task includes both desk studies and field surveys.

The desk studies involve collecting and reviewing drawings and other sources of information (as far back as the drawings accompanying the original Parliamentary Bill, the 1890s construction drawings, as well as later surveys and maps). Gathering this information involved searches in the National Archives, North Devon Records Office and other bodies. There are some gaps in this historical information, particularly in terms of details of the earthworks.

The field surveys assess what is present on the ground today. A great deal of tramping through muddy areas in wellington boots, and digging holes, is needed, and drainage of surface water from the land into streams was a recurring theme, the result of eighty years of neglect of culverts under the trackbed, and the erosion of embankments and cuttings, particularly in the recent heavy rainfall. So, wet areas of land shown on maps that predate the railway are often still wet today, and in some cases the water has run off along the old trackbed for years. We saw photographs showing the form of construction of all the embankments, bridges and culverts on the section from Wistlandpound to Blackmoor.

For the Planning Applications, a number of localised surveys of earthworks were carried out on the ground, using traditional instruments. For construction work, more detail is needed, so a drone survey was carried out to acquire overlapping high-resolution aerial photographs, which are combined to provide a coherent 3D surface model (including structures, trees, etc.), and a corresponding 3D model of the underlying terrain. It was surprising to hear that all the Phase 2A drone survey was completed in a single morning!

The surveying drone and its pilot. Photo: Chris Duffell

After a break for questions and discussion, Chris described how these 3D models are being used to establish the precise alignment for the rebuilt railway. Achieving this requires a clearly-defined structure and load gauge for the line. The original structure gauge drawing has not been found, so a new one has had to be developed. The new track alignment must be ‘threaded’ through the many surviving structures, across embankments and through cuttings, whilst incorporating improvements such as transition curves to reduce rail and wheel wear.

It was a tight squeeze in there… Maybe next time we need to book a larger room. Photo: Sue Barnard

After the main presentations, Chris showed us the 3D model of Parracombe bank, and allowed us to ‘fly’ over a section of the line in a movie created from the drone survey photographs ‘draped over’ the 3D surface model. We were also able to inspect some of the drawings and tables of infrastructure details that have been produced.

Chris stressed that there are no ‘show-stopper’ issues – in restoring the railway it is a case of finding the best solution in each area to correct existing problems that result from neglect and erosion, and to replace lost structures.

The twenty L&B members and visitors present enthusiastically thanked Chris for an interesting and educational afternoon.

Some books, including the group’s one remaining copy of “The Lynton & Barnstaple Railway – A Celebration” and two more of James Bloomfield’s excellent photographic prints were sold at the meeting.

*****

The next L&B-related event in the area will be on Thursday 8th March, when Bob Barnard will venture over the Welsh border to give his talk “The Lynton & Barnstaple Railway – Then and Now” to the Gwynedd Engineering Society, at Bangor University.

Bob Barnard

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