G&J Surveys - Moelwyn Mawr North Ridge Top - UKHillwalking Article

UKHillwalking have published an article on the survey of Moelwyn Mawr North Ridge Top conducted by G&J Surveys.  The original article and a link to it on the UKHillwalking website appear below.  Moelwyn Mawr North Ridge Top is a name coined for the hill by John and Anne Nuttall.

Wales Loses a Mountain

by John Barnard, Graham Jackson & Myrddyn Phillips (G&J Surveys)

John Barnard, Graham Jackson & Myrddyn Phillips, who make up the prolific amateur hill surveying team G&J Surveys, have been responsible for a number of well publicised revisions of hill heights in recent years. Their latest target, a northern top of Moelwyn Mawr, had been classified as a 2000-foot mountain in the more or less definitive Nuttalls list. But it turns out this peak does not make the grade after all, and as a result the number of listed mountains in Wales has been dropped to 189.

A “Nuttall” is defined as a mountain that is 2000ft or higher and has 15m or more of drop, or height difference between the summit and the bwlch (col) that connects it to the next higher hill. The list was compiled by John and Anne Nuttall, and detailed in their best selling guidebook ‘The Mountains of England & Wales – Vol 1 Wales’ (there's an English volume too).

Moelwyn Mawr North Ridge Top - a mountain no more

To check on many of the marginal tops included in their guides they pioneered a surveying technique recommended by Ordnance Survey. Both guides are highly recommended and their contents must have been a labour of love to produce.

However, the total number of Welsh ‘Nuttalls’ was not always the 190 given in the latest edition of the guidebook. When the 1st edition of this book was published in 1989, the total number of Welsh ‘Nuttall’ mountains stood at 181. The difference between these totals resulted from a number of surveys conducted by a few hill walking enthusiasts. However these surveys have differed in their accuracy, as some were conducted using a basic levelling technique whilst others have employed cutting edge technology.

Initially the inclusion of ‘new’ mountains in this list was due to basic levelling surveys, which are now known to have an uncertainty in height measurement of about +/- 1m for hills with 15m of drop. The technique relies upon standing at a col and sighting along a fixed spirit level that is attached to a wooden staff of known height, to a point level with it on the hill and repeating the process until the summit is reached. The total number of staff lengths then gives the drop. Although this method is basic, it has produced measurements for many hills that have been accepted into several well-known lists, including the Nuttalls, the Deweys and the Pedwarau.

Subsequent surveys have been carried out by line survey which uses a surveyor’s professional level and staff. This is the most accurate method to measure drop and can easily achieve accuracies to within 0.01m, assuming correct identification of summit and col. This method was used by Harold Morris and Tudur Owen on a top to the north of Cnicht in the Moelwynion (Moelwyns), and by Harold Morris, Dewi Jones, John Williams and Myrddyn Phillips on Waun Garnedd y Filiast in the Arennig (Arenigs), both hills subsequently entered the ranks of Welsh ‘Nuttalls’. Latterly John Barnard and Graham Jackson used a professional level and staff in the deletion of a top to the north of Cadair Fronwen in the Berwyn (seehere)

In order to measure if a mountain exceeds 2000ft in height a different surveying technique is required. Today these measurements are carried out using GNSS (Global Navigation Satellite System) receivers which work on the same principle as your car’s SATNAV. With the assistance of Leica Geosystems UK, a team taking in many of the individuals already mentioned in this article used a survey grade GNSS receiver to measure the height of Mynydd Graig Goch, which is situated at the western end of Crib Nantlle in Snowdonia, and found that it just exceeded 2,000ft in height. 

John and Graham beside the Leica GS15 at the bwlch of Moelwyn Mawr North Ridge Top

One of these marginal hills is situated on the northern ridge of Moelwyn Mawr in the Moelwynion in Snowdonia. It was included in John and Anne’s list to the 2000ft mountains of Wales, because Myrddyn Phillips surveyed it using his basic levelling technique and measured the drop to be just 50ft (15.2m). This was later remeasured by John and Anne Nuttall and others in independent surveys using basic techniques and their results confirmed that of Myrddyn Phillips. However, as mentioned earlier, this form of surveying method has a +/- 1m margin of uncertainly in height associated with it and the measured height was just 0.2m over 15m, much less than the measurement uncertainty of the method.

This hill and others that have entered John and Anne’s list due to basic levelling surveys have been on G&J Surveys list of hills to survey for a number of years. The chance to venture up into the Moelwynion and accurately survey the top to the north of Moelwyn Mawr presented itself on Tuesday 17th June as the weather forecast seemed good. G&J Surveys have a long list of hills to survey in their “in tray” but this hill was one of their top 16 priorities to carry out over the next 12 months.

We met in the car park at Croesor and drove further up the valley where permission had been given for us to park. Although the route up the hill which follows a track to a disused quarry was relatively easy, the cloud base had lowered since early in the morning. This was not good as accurate measurements with a professional level and staff can be made very difficult in misty conditions.  We hoped that either the cloud would disperse or that its base would rise above our hill.

Thankfully conditions for using the level were not compromised, but the weather was not as forecast. It was more autumnal than that expected for the middle of June with temperatures of just 11C and a stiff breeze of 20mph. Consequently, a number of layers of clothing were added as we set up the level and staff and proceeded to take readings up the hill from its connecting col to its summit. Both of these points were identified using the level and staff. Once the survey was complete we repeated the process back down the hill to ascertain a closing error between the two surveys. This proved to be just 3mm which is an excellent result.

Whilst on the hill we also took an hour of data from the summit and col with the Leica GS15 and five minutes of data from each with the Trimble GeoXH 6000. Each piece of equipment would give us an absolute height for the col and the hill’s summit, and would also give us a comparison between the different surveying methods and different equipment.

And what is the result? Would this northern top of Moelwyn Mawr remain as a 2000ft mountain in the Nuttall’s list or would it be deleted to the ranks of “also rans”? The result came to 14.77m of drop and as this value is below the 15m required to qualify for a Nuttall, the hill is deleted from the ranks of Nuttall 2000ft mountains. The total in this list now stands at 189.

Please click {here} to see the original article published on the UKHillwalking website