Union Chain Bridge 1820 - Scottish Anchorages Revealed by Radar

Date September 2018

Event ID 1046209

Category Descriptive Accounts

Type Publication Account

Permalink http://canmore.org.uk/event/1046209

Preliminary findings of the joint research radar investigation to facilitate decision maing on the bridge's ongoing £8 million refurbishment indicate confirm that the that of the three differing Scottish side anchors (bridge managed by Scottish Borders and Northumberland County Council (NCC)) plate positions given in 1820/1 (no as-built drawings are known) at depths below ground at 40ft (12.2m) or 24ft (7.3m) or 13ft 10in (4.2m), Stevenson's 24ft is closest to the findings of the research group of 7.5m depth below the road top. If Captain Brown's statement that the plates 'are 40 feet under the road ' (Miller, 2017, 181) refers to the length of the buried chains on their 30 drgree inclination, this would be close to the radar indicated position. NCC plans to provide new anchorages and to remove and dispaly the present ones.

Stevenson, who corresponded with Captain Brown (original bridge designer) described the ends of the chains as passing through the "great anchor plates of cast iron into which they are stopped by by a straiong iron spear or bolt, of an oval form, of 3x3 1/2 in in thickness. The plates measured 6ft in length , 5ft in breadth and 5in in thickness in the central parts; but towards the end diminidh int thickness to 2 1/2 in...thus fixed [they] are loaded with mound stones and earthy matters to the level of the roadway" (Stevenson, Edinburgh Philosophical Journal, Oct, 1821).

The radar scan data plots of the anchor plates were not sufficiently definitive to indicate their precise form and dimensions although all indications from the data was indicative of the position of the plate.

R Paxton, 2018