Mapping Mountains – Hill Reclassifications – The Welsh P15s

Mynydd Mechell (SH 353 899) – Welsh Sub-P15 deletion

There has been a deletion to the list of The Welsh P15s, 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 Mynydd Mechell (SH 353 899)

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

The Welsh P15s – Welsh hills with 15m minimum drop, irrespective of their height, with an accompanying sub list entitled the Welsh Sub-P15s, with the criteria for this sub category being all Welsh hills with 14m or more and below 15m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list appearing on Mapping Mountains on the 10^th May 2019. 

The Welsh P15s by Myrddyn Phillips

The name the hill is listed by is Mynydd Mechell 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 the coast to its north and has minor roads to its north, south and east and the A5025 road to its west, and has the village of Llanfechell towards the north-east. 

When the listing that became known as The Welsh P15s was being compiled, this hill was included in the P14 sub list with an estimated c 14m of drop, based on the 82m summit spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and an estimated c 68m bwlch height, based on interpolation of 5m contouring between 65m – 70m that appears on the Ordnance Survey 1:25,000 Explorer map. 

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 Welsh Sub-P15 status is due to detail on contemporary maps produced from Ordnance Survey data and LIDAR analysis, resulting in an 80.3m summit height and an estimated c 68m bwlch height, with these values giving this hill an estimated c 12m 0f drop, which is insufficient for it to be classified as a Welsh Sub-P15. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Mynydd Mechell 

OS 1:50,000 map:  114

Summit Height:  80.3m (LIDAR)                                                           

Summit Grid Reference:  SH 35360 89987 (LIDAR) 

Bwlch Height:  c 68m (interpolation) 

Bwlch Grid Reference:  SH 35255 89745 & SH 35362 89116 & SH 35283 89513 (interpolation) 

Drop:  c 12m (LIDAR summit and interpolated bwlch) 

 

Myrddyn Phillips (September 2021)