The sleuths head to the hill to survey Moelwyn Mawr North Ridge top. Photo: Myrddyn Phillips

With upwards of 20,000 copies sold of John and Anne Nuttall’s guide to The Mountains of England & Wales – Volume 1: Wales, which is published by Cicerone, the book can lay claim to being one of the most popular guides to hills in Britain.

This book is a sister volume to another guide published by Cicerone and written by the same authors, which details routes to the 2,000ft mountains of England. The sales of these guides mean that when each copy is laid on top of another they would build a new 2,000ft high tower in its own right.

John and Anne Nuttall are prizewinning authors who live in Congleton and have expertise in writing guides that are informative, both from a current stand point and from an historical view, as their suggested routes around these mountains are full of anecdotal reference and historical information.

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

Their Welsh guide describes 48 circular walks that, if completed, guide the reader around the 190 hills qualifying for their list of 2,000ft mountains. A ‘nuttall’ is defined as a mountain that is 2000ft or higher and has 15m or more of drop, where drop is the height difference between the summit and the bwlch (col) that connects it to the next higher hill.

Graham and John beside the Leica GS15 at the summit of Moelwyn Mawr North Ridge top. Photo: Myrddyn Phillips

This book is now in its 4th edition, and along with its sales statistics, is a clear indicator of its popularity. However, the total number of Welsh nuttalls was not always that given in the latest edition of the guide book. When the first 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 hillwalking enthusiasts.

These surveys have differed in their accuracy, as some were conducted using a basic levelling technique while 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.

To measure if a mountain exceeds 2,000ft 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.

Moelwyn Mawr North Ridge top. Photo: Myrddyn Phillips

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.

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 2,000ft 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 17 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.

John and Graham beside the Leica GS15 at the bwlch of Moelwyn Mawr North Ridge top. Photo: Myrddyn Phillips

While 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 2,000ft 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 2,000ft mountains.

The total of Welsh Hills in this list now stands at 189.

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