Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

 

Pt. 39.7m (SH 299 859) – 30-99m Sub-Twmpau addition

There has been confirmation of an addition 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 LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR summit image of Pt. 39.7m (SH 299 859)

The criteria for the list that this addition 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 hill is being listed by the point (Pt. 39.7m) notation as an appropriate name for it either through local enquiry and / or historic research has not been found by the author, 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 a series of minor roads to its north, south and east and the coast to its west, and has the village of Llanfaethlu towards the north-east. 

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. 

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

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 21m of drop, based on the 39m summit and 18m bwlch spot heights that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage 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 bwlch image of Pt. 39.7m (SH 299 859)

Therefore, the confirmation of the addition of this hill to 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 39.7m summit height and a 19.2m bwlch height, with these values giving this hill 20.5m of drop, which is sufficient for it to be classified as a 30-99m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Pt. 39.7m 

OS 1:50,000 map:  114

Summit Height:  39.7m (LIDAR) 

Summit Grid Reference:  SH 29920 85948 (LIDAR) 

Bwlch Height:  19.2m (LIDAR) 

Bwlch Grid Reference:  SH 30092 86343 (LIDAR) 

Drop:  20.5m (LIDAR) 

 

Myrddyn Phillips (June 2021)