Tuesday, 14 July 2020

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

Esgair y Maesnant (SN 832 862) – Dewey deletion

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.

The summit of Esgair y Maesnant (SN 832 862)

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:

25th 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:

29th 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.

25th 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 was listed by in the Deweys is Esgair y Maesnant, and it is adjoined to the Pumlumon group of hills which are situated in the central part of Wales, and it is positioned with the A44 road to its south, and has the town of Llanidloes towards the east.

This hill was not included in the original 1995 Constable publication, but with a 504m summit spot height and bwlch contouring between 470m – 480m that appear on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, this hill was noted as an outside possibility for a potential new Dewey.

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

The above detail was noted by Myrddyn Phillips who then conducted a basic levelling survey (BLS) of this hill on the 11th July 2000, resulting in 95½ft / 29.1m of drop.  These details were forwarded to the list author; Michael Dewey along with other recent results produced from basic levelling surveys.

Although surveyed as having less than the minimum 30m of drop required to enter this list, the hill was inadvertently included by Michael Dewey.  Its inclusion was subsequently noted during proof reading when an updated copy of the list was received by Myrddyn Phillips.  This hill’s deletion from Dewey status was confirmed in a letter received from the author dated 7th August 2000.  Although its inclusion in this list was an error, it was for a short period of time listed as a Dewey and therefore the details of this hill are appearing in this Hill Reclassification post and the forthcoming Change Register.

The Trimble GeoXH 6000 gathering data at the summit of Esgair y Maesnant

The Trimble GeoXH 6000 gathering data at the bwlch of Esgair y Maesnant

As the margin of uncertainty for the BLS method of surveying over terrain such as that on this hill is approximately +/- 2m and as the resulting 29.1m of drop was near the minimum 30m qualifying drop value, this hill was prioritised for a GNSS survey, and this took place on the 18th July 2016.  The summit and bwlch of this hill were surveyed by Myrddyn Phillips using a Trimble GeoXH 6000, resulting in a 503.6m summit height and a 476.2m bwlch height, with these values giving this hill 27.3m of drop, and confirming its non-Dewey status.

The full details for the hill are:

Name:  Esgair y Maesnant

OS 1:50,000 map:  135, 136

OS 1:25,000 map:  214

Summit Height:  503.6m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 83220 86275 (Trimble GeoXH 6000)

Bwlch Height:  476.2m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SN 82792 86427 (Trimble GeoXH 6000)

Drop:  27.3m (Trimble GeoXH 6000)

Myrddyn Phillips (July 2020)

No comments: