Triangulation Points

I like collecting things. Triangulation points are a favourite along with benchmarks that can be found along a walk or near to one.

There is something very satisfying about reaching a trig pillar, partly I guess because they invariably involve a walk up hill and a reward of sweeping views, weather permitting. There are 84 pillars within the Peak District National Park boundary and many more triangulation points and thousands more benchmarks.

Some are not shown on maps with the traditional blue triangle, the one at Hey Edge for instance, built but never used for triangulation, but was used for levelling, so does it not qualify for the blue triangle.

Some triangulation points are not even pillars. One of my walks takes in the Hunting Tower on the Chatsworth Estate, the triangulation point being the flagstaff. Another is the centre of the spire of All Saints Church in Bakewell.

With the advent of GPS the triangulation pillar network became largely redundant, but a few still do have a purpose. The pillar at Harland South, levelling bracket number 2998 is part of the Global Positioning Network and as such is protected by Ordnance Survey. A plate informs the visitor that any damage should be reported to the phone number.

Triangulation points always come in a minimum of three so a favoured walk of mine takes in the Hunting Tower at Chatsworth, the pillar at Birchen Edge along with the Three Ships and the pillar at Harland South, passing Hobs House, one of the first ancient monuments to have legal protection in the UK, on the way. Two pillars, one part of the Global Positioning System and one flagstaff on a hunting tower. Not bad for a day out.

Changing landscapes

thumb_untitled_1024
Derwent Village, Upper Derwent Valley, Peak District National Park.  Reproduced with the permission of the National Library of Scotland     http://maps.nls.uk/index.html

A changing landscape has always fascinated me. I think the interest comes when I find out things are there that I never even knew about. I have a boyish attraction to the man made artefacts that were once of use and even important but now are long forgotten.

Benchmarks are a particular delight when I find one. A friend and fellow Ranger sent me a picture of one this week and it prompted me to look for more, so I got out my old maps and started to look.

The map above is from a survey in 1880 and it shows the now submerged village of Derwent. You can still walk around the village when the waters or low, discerning streets and boundary walls. Some of the village still exists, the school for instance, the one at the top, not in the village, I had not realised there were two. The gates to the Vicarage can be seen but the building along with Derwent Hall and the church have long gone. Grindle Barn is still there although the path up now sets off from a different place.

What is interesting are the OS benchmarks. There is one by the road between the upper school building and Wellhead at a height of 712 feet and 4 inches. Something to go and seek out next time I am there.

 

Ordnance Survey Benchmarks

thumb_P1000537_1024
Benchmark at Moscar SK 2305 8759

This is a levelling benchmark placed and used by Ordnance Survey. Its location is SK 2305 8759 at Moscar on the footpath from the A57 towards Stanage. The mark was made in 1961, is of the third order of surveying and is 600mm above ground level. Its datum is Newlyn. Originally the mark and boulder were on the west of the footpath but time and boots have now placed it east of the path.

There are some 500,000 benchmarks on the UK mainland, most no longer in use. They identify the height at a given point. The base line is the tidal measuring station at Newlyn in Cornwall, that is the point where all height measurements are taken from, including the 190 Fundamental Benchmarks which were the first order and therefore the most accurate, set in chambers deep underground on bedrock , these benchmarks are still in use today by the Global Positioning System for calculating the accuracy of the height calculation.

SK 24532 94653 Broomhead Moor Fundemental Benchmark TP0526 Chamber
SK 24532 94653 Broomhead Moor Fundamental Benchmark TP0526 Chamber