Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

Pen Ucheldref (SH 349 882) – 30-99m Sub-Twmpau deletion

There has been a deletion to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data and LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pen Ucheldref (SH 349 882)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Pen Ucheldref and this was derived from the Tithe map, and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with two minor roads beside its summit and the A5025 road to its north-west, and has the village of Llanrhuddlad also towards the north-west. 

When the original 30-99m height band of Welsh P30 hills were 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 23m of drop, based on an estimated c 90m summit height and an estimated c 67m bwlch height, with both heights based on interpolation of 5m contouring that appears on the Ordnance Survey 1:25,000 Explorer map, with the 85m upper summit contour mistaken for 90m. 

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 deletion of this hill from 30-99m Sub-Twmpau status is due to a combination of detail on contemporary maps produced from Ordnance Survey data and LIDAR analysis, resulting in an 85.4m summit height and an estimated c 67m bwlch height, with these values giving this hill an estimated c 18m of drop, which is insufficient for it to be classified as a 30-99m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Pen Ucheldref 

OS 1:50,000 map:  114

Summit Height:  85.4m (LIDAR) 

Summit Grid Reference:  SH 34917 88259 (LIDAR) 

Bwlch Height:  c 67m (interpolation) 

Bwlch Grid Reference:  SH 35183 88544 (interpolation) 

Drop:  c 18m (LIDAR summit and interpolated bwlch) 

 

Myrddyn Phillips (July 2021)