Mapping Mountains – Significant Height Revisions – 500m Twmpau and Welsh Highlands – Uchafion Cymru

 

Blorens (SO 269 118) 

There has been a Significant Height Revision to a hill that is listed in the 500m Twmpau and 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 and LIDAR analysis conducted by Aled Williams and Myrddyn Phillips. 

Blorens (SO 269 118)

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

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with an accompanying sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or above 500m and below 600m in height that have 20m or more and below 30m of drop.  With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips and is published on Mapping Mountains in Google Doc format.

The 500m Twmpau by Myrddyn Phillips

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 Blorens and it is adjoined to the Cefn yr Ystrad group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A465 road to its north-east, the B4246 road to its north-west and a minor road to its south, and has the town of Y Fenni (Abergavenny) towards the north-east.

When the list of Welsh 500m P15s that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 133m of drop, based on the 561m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 428m bwlch height, based on interpolation of 10m contouring between 420m – 430m. 

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

The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in a 558.9m summit height positioned at SO 26974 11830, 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 Blorens 

Therefore, the new listed summit height of this hill is 558.9m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SO 26974 11830 and is 2.1m lower than its originally listed height of 561m, which was based on the summit spot height that appears on the 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:  Cefn yr Ystrad

Name:  Blorens

OS 1:50,000 map:  161

Summit Height (New Height):  558.9m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SO 26974 11830 (Trimble GeoXH 6000)  

Bwlch Height:  426.9m (LIDAR)

Bwlch Grid Reference:  SO 21949 10939 (LIDAR)

Drop:  132.0m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Aled Williams and Myrddyn Phillips (March 2023)