Mapping Mountains – Significant Height Revisions – Welsh Highlands – Uchafion Cymru

 

Castell y Gwynt (SH 653 581) 

There has been a Significant Height Revision to a hill that is listed in the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from two Trimble GeoXH 6000 surveys conducted by Myrddyn Phillips on the 16.05.14 and Aled Williams on the 04.03.23. 

Castell y Gwynt (SH 653 581)

The criteria for the list that this height revision applies to are:

Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop.  This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Castell y Gwynt and it is adjoined to the Glyder Fawr group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A5 road to its north and the A4086 road to its south, and has the village of Capel Curig towards the east.

When the list that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with 16m of drop, based on a series of basic levelling surveys conducted by Myrddyn Phillips and listed with a 972m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and a 956m bwlch height, based on the height difference between the summit spot height and the drop value ascertained from the basic levelling survey. 

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

The summit of this hill has now been surveyed twice with the Trimble GeoXH 6000 and it is the average of these results that is being taken, resulting in a 975.7m summit height positioned at SH 65397 58181, and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. 

The Trimble GeoXH 6000 gathering data at the summit of Castell y Gwynt on the 16.05.14

Therefore, the new listed summit height of this hill is 975.7m and this was derived from the average of two Trimble GeoXH 6000 surveys, this is positioned at SH 65397 58181 and is 3.7m higher than its previously listed height of 972m which was based on the summit spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Glyder Fawr

Name:  Castell y Gwynt

OS 1:50,000 map:  115

Summit Height (New Height):  975.7m (converted to OSGM15)

Summit Grid Reference:  SH 65397 58181  

Bwlch Height:  959.7m (converted to OSGM15)

Bwlch Grid Reference:  SH 65419 58194

Drop:  16.0m

 

Myrddyn Phillips and Aled Williams (May 2023)