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

Craig Eigiau (SH 712 646) 

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 a Trimble GeoXH 6000 survey conducted by Aled Williams. 

Craig Eigiau (SH 712 646) (Photo: Aled Williams)

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 Craig Eigiau and it is adjoined to the Carnedd Llywelyn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with a minor road to its north-east, the A5 road to its south-west and the B5106 road and the A470 road to its east, and has the town of Llanrwst towards the east south-east.

The contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map do not show any meaning contours for this hill that imply its true height, as each only has an uppermost 670m contour. 

Extract from the Ordnance Survey 1:25,00 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

LIDAR analysis gives this hill 9.7m of drop, based on a 688.1m summit height and a 678.4m bwlch height.  This hill has now been surveyed with the Trimble GeoXH 6000, resulting in a 688.4m summit height positioned at SH 71280 64670 and it is this result that is being prioritised for this hill, and this summit 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 Craig Eigiau (SH 712 646) (Photo: Aled Williams)

Therefore, the new listed summit height of this hill is 688.4m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SH 71280 64670 and is 18.4m higher than the uppermost 670m contour on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are: 

Group:  Carnedd Llywelyn

Name:  Craig Eigiau

OS 1:50,000 map:  115

Summit Height (New Height):  688.4m (converted to OSGM15)

Summit Grid Reference:  SH 71280 64670

Bwlch Height:  678.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 71218 64674   

Drop:  10.2m 

 

Aled Williams and Myrddyn Phillips (April 2023)