Mapping Mountains – Hill Reclassifications – The 500-Metre Tops of England and Wales – Deweys

Lledwyn Mawr (SH 904 287) – Dewey addition

This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Deweys and where I have had direct association with the status change.  These posts will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the Mountain tables book. 

Lledwyn Mawr (SH 904 287)

The 500-Metre Tops of England and Wales are affectionately known after their hill list compiler; Michael Dewey.  This list mixes metric and imperial height in its criteria to bookend up to the 2000ft height band and takes in all hills in England, Isle of Man and Wales that are 500m and above and below 2000ft (609.6m) in height that have 30m minimum drop.

This list formed one of a number of lists that appeared in the Mountain tables book published by Constable in 1995 and at the time of publication comprised 373 hills with 164 in England, 5 in the Isle of Man and 204 in Wales.  The Deweys have undergone extensive revision since first publication with the initial stages forming the basis of this revision given below:

1995    Mountain tables published by Constable with 373 hills listed as Deweys.

April 2000    Strider (LDWA quarterly booklet) publishes contact details for David Purchase and Myrddyn Phillips who have found and list 24 and 14 possible new 500m tops respectively.

It was expanded versions of the above two lists that formed the basis of the next publication:

25^th May 2000    List of Possible 500 Metre Tops by Michael Dewey listing 44 hills.

David Purchase expands his Additional Dewey 500m Hills and Myrddyn Phillips produces lists of English 500m hills to measure and Welsh 500m hills to measure.

These lists formed the basis of the next publication:

29^th June 2000    Possible/Probable 500’s by Michael Dewey listing 77 hills.  Michael adopts following protocol; if one person proposes that a top should qualify as a 500 by personal survey, and is then confirmed by a second person, it should then be promoted to the main list.

April 2002    The 500+ Tops of England and Wales – The ‘New Deweys’ published in the Strider booklet and listing 66 new qualifying hills.

25^th May 2006    Rob Woodall republishes Michael’s main and possible/probable lists on the RHB Yahoo group file database. 

Mountain tables by Michael Dewey

The details for this addition appear below:

The name the hill is listed by in the Deweys is Lledwyn Mawr, and it is adjoined to the Aran group of hills which are situated in the southern part of North Wales, and it is positioned with the B4403 road to its north, the A494 road to its west and the B4391 road to its east, and has the town of Y Bala towards the north north-east.

This hill was not included in the original 1995 Constable publication, but with a 527m summit spot height and bwlch contouring between 490m – 500m that appear on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, the interpolated drop value was estimated sufficient for this hill to be a potential new Dewey.

Extract from the Ordnance Survey 1:25,000 Explorer map

The above detail was noted by David Purchase and Myrddyn Phillips who worked independently but also exchanged all data.  On the 7^th July 2000 Myrddyn Phillips conducted a basic levelling survey (BLS) of this hill, resulting in 99½ft / 30.3m of drop.  These details were forwarded to the list author; Michael Dewey and the hill was added to the list with the date of survey given in the Remarks column accompanying the list.

As the margin of uncertainty for the BLS method of surveying over terrain such as that on Lledwyn Mawr is approximately +/- 1.5m and as the resulting 30.3m of drop was near the minimum 30m qualifying drop value, this hill was prioritised for a GNSS survey, and this took place on the 2^nd and 8^th February 2012.  The summit and bwlch of this hill were surveyed by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530, with 60 minutes of data gathered at the summit and 90 minutes at the bwlch on the first day’s survey and 60 minutes at the bwlch on the second day’s survey.

Gathering data during the first bwlch survey

The survey resulted in a 526.1m summit height and a 495.1m bwlch height, with these values giving this hill 30.9m of drop, and confirmed this hill’s Dewey status. 

The full details for the hill are:

Name:  Lledwyn Mawr

OS 1:50,000 map:  125

OS 1:25,000 map:  23

Summit Height:  526.1m (converted to OSGM15, Leica 530)

Summit Grid Reference:  SH 90498 28742 (Leica 530)

Bwlch Height:  495.1m (converted to OSGM15, Leica 530)

Bwlch Grid Reference:  SH 90897 28658 (hand-held GPS via DoBIH)

Drop:  3o.9m (Leica 530)

Myrddyn Phillips (June 2020)