Mapping Mountains – Hill Reclassifications – Y Trichant – The 300m Hills of Wales

Warren Bank (SO 138 703) – Sub-Trichant addition 

There has been an addition to the list of Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Warren Bank (SO 138 703)

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

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Warren Bank 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 encircled by minor roads with the B4356 road farther to its north, the A483 road farther to its west and the A488 road farther to its south-east, and has the village of Llanbister towards the north-west. 

When the original 300m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 22m of drop, based on the 349m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 327m bwlch height based on interpolation of 10m contouring between 320m – 330m. 

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 Warren Bank (SO 138 703)

The result produced by LIDAR analysis confirms this hill as having over 20m of drop, and as the summit has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes. 

The Trimble GeoXH 6000 gathering data at the summit of Warren Bank

Therefore, the addition of this hill to Sub-Trichant status is due to LIDAR analysis and a subsequent Trimble GeoXH 6000 survey, resulting in a 348.5m summit height and a 325.5m bwlch height, with these values giving this hill 23.0m of drop, which is sufficient for it to be classified as a Sub-Trichant. 

 

The full details for the hill are: 

Group:  Beacon Hill 

Name:  Warren Hill 

OS 1:50,000 map:  136, 148

Summit Height:  348.5m (converted to OSGM15, Trimble GeoXH 6000)                                                           

Summit Grid Reference:  SO 13803 70384 (Trimble GeoXH 6000) 

Bwlch Height:  325.5m (LIDAR) 

Bwlch Grid Reference:  SO 13603 70747 (LIDAR) 

Drop:  23.0m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (August 2021)