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

Knowle Hill (SO 213 617) – Sub-Trichant reclassified to Trichant 

There has been confirmation of a reclassification 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 and assisted by Aled Williams. 

Knowle Hill (SO 213 617)

The criteria for the list that this reclassification 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 Knowle Hill and it is adjoined to the Fforest Glud group of hills, which are situated in the eastern part of Mid and West Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its west, the B4372 road to its south-east and the A44 road farther to its south-east, and has the village of Maesyfed (New Radnor) towards the south. 

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

After 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 29m of drop, based on the 387m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and the 1:25,000 Explorer map and an estimated c 358m bwlch height based on interpolation of 5m contouring between 355m – 360m that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

Since the publication of the P30 lists of Geoff Crowder’s v-g.me website there have been a number of Ordnance Survey maps made available online, some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website, whilst others are current and digitally updated such as the old Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

The details for this hill were reassessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available maps and for this hill it had a 357m bwlch spot height positioned at SO 21437 61979, and when coupled with the 387m summit spot height gave this hill 30m of drop. 

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 Knowle Hill (SO 213 617)

The result produced by LIDAR analysis confirms this hill as having over 30m 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 Knowle Hill

Therefore, the confirmation of the reclassification of this hill from Sub-Trichant status is due to LIDAR analysis and a subsequent Trimble GeoXH 6000 survey, resulting in a 387.9m summit height and a 357.7m bwlch height, with these values giving this hill 30.2m of drop, which is sufficient for it to be classified as a Trichant. 

 

The full details for the hill are: 

Group:  Fforest Glud 

Name:  Knowle Hill 

OS 1:50,000 map:  137, 148

Summit Height:  387.9m (converted to OSGM15, Trimble GeoXH 6000)                                                           

Summit Grid Reference:  SO 21397 61735 (Trimble GeoXH 6000) 

Bwlch Height:  357.7m (LIDAR) 

Bwlch Grid Reference:  SO 21337 61955 (LIDAR) 

Drop:  30.2m (Trimble GeoXH 6000 and LIDAR bwlch) 

 

Myrddyn Phillips (August 2021)