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

Orddu (SH 963 423) – 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.

Orddu (SH 963 423)

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 Orddu, and it is adjoined to the Arenig group of hills which are situated in the north-western part of north Wales, and it is positioned with the A5 road to its north-east, the B4501 road to its west and the A494 road to its south-east, and has the town of Y Bala towards the south south-west.

This hill was not included in the original 1995 publication, but with a 555m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and bwlch contouring between 520m – 530m on the 1:50,000 Landranger and 1:25,000 Explorer map, the interpolated drop value was estimated sufficient for this hill to be a 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 29^th March 2000 and the 16^th April 2000 Myrddyn Phillips conducted a basic levelling survey (BLS) of this hill, resulting in the average of these two surveys being 112½ft / 34.3m of drop.  These details were forwarded to the list author; Michael Dewey and the hill was added to the list on the 3^rd May 2000.

Extract from the Magic Maps website

Since the inclusion of this hill in the Dewey list the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and gives a 521m spot height on the area of this hill’s bwlch, and when coupled with the 555m summit spot height these values give this hill 34m of drop.  The 521m spot height is also shown on Ordnance Survey data that appears on the Magic Maps website.

Gathering data at the summit of Orddu

Gathering data at the bwlch of Orddu

As the drop from the BLS survey and summit and bwlch spot heights is close to the minimum 30m qualifying drop value, this hill was prioritised for a GNSS survey, and this took place on the 19^th January 2020.  The summit and bwlch of this hill were surveyed by Myrddyn Phillips and Aled Williams using a Trimble GeoXH 6000, resulting in a 553.8m summit height and a 520.5m bwlch height, with these values giving this hill 33.3m of drop and confirming its Dewey status.

The full details for the hill are:

Name:  Orddu

OS 1:50,000 map:  125

OS 1:25,000 map:  18

Summit Height:  553.8m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 96338 42337 (Trimble GeoXH 6000)

Bwlch Height:  520.5m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SH 95886 42428 (Trimble GeoXH 6000)

Drop:  33.3m (Trimble GeoXH 6000)

Myrddyn Phillips (April 2020)