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

Moel Bowydd (SH 712 470)

There has been a Significant Height Revision to the listing of the Yr Uchafion, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams, with a subsequent Trimble Ge0XH 6000 survey conducted by Myrddyn Phillips and Aled Williams confirming its status.

Moel Bowydd (SH 712 470)

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

Yr Uchafion (Latterly named The Welsh Highlands - Uchafion Cymru) - This is the draft title for a list of the Welsh 500m P15s that takes in all Welsh hills at or above 500m in height that have a minimum 15m of drop.  Accompanying the main list are three sub lists; the 500m Sub-Uchaf, 490m Sub-Uchaf and the Double Sub-Uchaf category.  The criteria for 500m Sub-Uchaf status is all Welsh hills at or above 500m in height that have 14m or more and below 15m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the details relating to this list published on the Mapping Mountains site in November 2015.

The Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The name the hill is listed by is Moel Bowydd, and it is adjoined to the Arenig Fach group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and it is positioned with the A470 road to its west, and has the town of Blaenau Ffestiniog towards the south-west.

 

This hill is given an uppermost 490m ring contour with no spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and has bwlch contouring between 480m – 490m, and prior to the analysis of LIDAR the hill was unclassified.

Extract from the Ordnance Survey 1:25,000 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 image of Moel Bowydd (SH 712 470)

LIDAR analysis resulted in the addition of this hill to Uchaf status.  The hill has subsequently been surveyed using the Trimble GeoXH 6000, resulting in a 500.5m summit and when compared to the uppermost 490m ring contour on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, this 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 Moel Bowydd (SH 712 470)

Therefore, the new listed summit height of this hill is 500.5m and this was derived from a Trimble GeoXH 6000 survey, and 10.5m higher than the 490m uppermost ring contour on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group:  Arenig Fach

Name:  Moel Bowydd

OS 1:50,000 map:  115

Summit Height (New Height):  500.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 71272 47051 (Trimble GeoXH 6000)

   

Bwlch Height:  482.8m (LIDAR)

Bwlch Grid Reference:  SH 71598 47215 (LIDAR)

Drop:  17.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips and Aled Williams (May 2017)