Mapping Mountains – Hill Reclassifications – The Welsh Highlands – Uchafion Cymru

Cwar Blaen Dyffryn (SO 098 148) – 490m Sub-Uchaf addition

There has been an addition to the listing of The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams.

LIDAR image of Cwar Blaen Dyffryn (SO 098 148)

The criteria for the list that this addition applies to are:

The Welsh Highlands – Uchafion Cymru – This is the revised draft title for the Welsh 500m P15s list that takes in all hills in Wales at or above 500m in height with 15m minimum drop.  Accompanying the main list are three sub lists, these are; 500m Sub-Uchaf, 490m Sub-Uchaf and the Double Sub category, with this hill being added as a 490m Sub-Uchaf.  The criteria for which are all Welsh hills at or above 490m and below 500m in height with 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams with the Introduction to the list being published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19th June 2019.

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

The name the hill is listed by is Cwar Blaen Dyffryn, and it is adjoined to the Cefn yr Ystrad group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is positioned directly above the end of a minor road, and also has the A40 road to its north-east, the A470 road to its west and the A465 road to its south, and has the village of Trefil towards the south-east.

When the two 490m sub categories were added as a part of the Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru, this hill was not included as contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps do not give the hill uppermost contours or a spot height.

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.

Therefore, the addition of this hill to 490m Sub-Uchaf status is due to LIDAR analysis, resulting in a 496.0m summit height and a 477.6m bwlch height, with these values giving this hill 18.4m of drop.

The full details for the hill are:

Group:  Cefn yr Ystrad

Name:  Cwar Blaen Dyffryn

OS 1:50,000 map:  161

Summit Height:  496.0m (LIDAR)

Summit Grid Reference:  SO 09829 14840 (LIDAR)

Bwlch Height:  477.6m (LIDAR)

Bwlch Grid Reference:  SO 09694 14900 & SO 09698 14902 (LIDAR)

   

Drop:  18.4m (LIDAR)

 

For the additions, deletions and reclassifications to The Welsh Highlands – Uchafion Cymru reported on Mapping Mountains please consult the following Change Registers:

The Welsh 500m P15s (Yr Uchafion)

The Welsh 500m P15s (Yr Uchafion) – 500m Subs

The Welsh 500m P15s (Yr Uchafion) – 490m Subs

The Welsh 500m P15s (Yr Uchafion) – Double Subs

Aled Williams and Myrddyn Phillips (November 2020)