Mapping Mountains – Hill Reclassifications – Y Pedwarau – The 400m Hills of Wales

 

Stonewall Hill (SO 318 696) – 400m Sub-Pedwar addition

There has been an addition to the listing of the Y Pedwarau – The 400m Hills of Wales under the classification of National Top status (for details relating to the concept of National Tops see separate post), with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams. 

Stonewall Hill (SO 318 696)

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

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being added to the 400m Sub-Pedwar category.  The criteria for 400m Sub-Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Stonewall Hill and it is adjoined to the Beacon Hill group of hills, which are situated in Mid and West Wales (Region B, Sub-Region B1), and it is positioned with the A4113 road to its north, a minor road to its immediate west and the B4355 road farther to its west, and has the town of Trefyclo (Knighton) towards the north-west.

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

Extract from the Ordnance Survey series of Six-Inch maps showing the course of the border

Extract from the Magic Maps website showing the course of the border

When the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013, this hill was not included as the concept of National Tops had not been devised.  The hill was subsequently analysed using contemporary Ordnance Survey maps and LIDAR for height and drop.  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 Stonewall Hill (SO 318 696)

LIDAR analysis confirms this hill as over 400m in height, and as the summit has now been surveyed with the Trimble GeoXH 6000, it is this result that is being prioritised for listing purposes. 

Gathering data at the summit of Stonewall Hill

Therefore, the confirmation of the addition of this hill to 400m Sub-Pedwar status under the National Top classification is due to LIDAR analysis and a subsequent Trimble GeoXH 6000 survey, resulting in a 400.1m summit height and a 376.4m bwlch height, with these values giving this hill 23.8m of drop which is sufficient for it to be classified as a 400m Sub-Pedwar. 

 

The full details for the hill are:

Group:  Beacon Hill 

Name:  Stonewall Hill

OS 1:50,000 map:  137, 148

Summit Height:  400.1m (converted to OSGM15)

Summit Grid Reference:  SO 31823 69655

Bwlch Height:  376.4m (converted to OSGM15)

Bwlch Grid Reference:  SO 31273 70279

Drop:  23.8m

 

For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales reported on Mapping Mountains since the May 2013 publication of the list by Europeaklist please consult the following Change Registers:

 

Y Pedwarau

 

Y Pedwarau – 400m Sub-Pedwarau

 

Y Pedwarau – 390m Sub-Pedwarau

 

Y Pedwarau – 390m Double Sub-Pedwarau

 

Aled Williams and Myrddyn Phillips (October 2021)