Grough 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 Grough website appear below. Moelwyn Mawr North Ridge Top is a name coined for the hill by John and Anne Nuttall.
Hill sleuths go in search of truth about Welsh Nuttall Moelwyn Mawr
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| The sleuths head to the hill to survey Moelwyn Mawr North Ridge Top |
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.
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| Graham and John beside the Leica GS15 at the summit of Moelwyn Mawr North Ridge Top |
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.
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| Moelwyn Mawr North Ridge Top |
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.
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| John and Graham beside the Leica GS15 at the bwlch of Moelwyn Mawr North Ridge Top |
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)
Please click {here} to see the original article
published on the Grough website
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