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

 

Sheep Pasture (SN 935 821) – Sub-Trichant deletion 

There has been a deletion 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. 

Sheep Pasture (SN 935 821)

The criteria for the list that this deletion 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 Sheep Pasture and this was derived from the Tithe map and it is adjoined to the Pumlumon group of hills, which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with a minor road to its north-west and the A470 road to its south-east, and has the town of Llanidloes towards the north-east. 

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. 

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 21m of drop, based on the 356m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 335m bwlch height based on interpolation of 10m contouring between 330m – 340m. 

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 Sheep Pasture (SN 935 821)

The result produced by LIDAR analysis gives this hill less than 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 Sheep Pasture

Therefore, the deletion of this hill from Sub-Trichant status is due to LIDAR bwlch analysis and a Trimble GeoXH 6000 summit survey, resulting in a 355.3m summit height and a 336.4m bwlch height, with these values giving this hill 18.9m of drop, which is insufficient for it to be classified as a Sub-Trichant.

 

The full details for the hill are: 

Group:  Pumlumon 

Name:  Sheep Pasture 

OS 1:50,000 map:  136

Summit Height:  355.3m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 93587 82145 (Trimble GeoXH 6000) 

Bwlch Height:  336.4m (LIDAR) 

Bwlch Grid Reference:  SN 93150 82163 (LIDAR) 

Drop:  18.9m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (November 2021)