Mapping Mountains – Hill Reclassifications – The Welsh P15s

Caer Helen (SH 325 780) – Welsh P15 addition

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

LIDAR image of Caer Helen (SH 325 780)

The criteria for the list that this addition 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 Caer Helen and this was derived from the Ordnance Survey series of Six-Inch maps 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 west, the A5 and A55 roads to its north and minor roads to its west and south, and has the village of Llanfiangel-yn-Nhywyn towards the south-west. 

When the listing that became known as The Welsh P15s was being compiled, this hill was not included in either the main P15 list or the accompanying P14 sub list, but it was documented with an estimated c 13m of drop, based on the 34m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 21m bwlch height, based on interpolation of 5m contouring between 20m – 25m. 

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 addition of this hill to Welsh P15 status is due to LIDAR analysis, resulting in a 33.9m summit height and a 17.4m bwlch height, with these values giving this hill 16.5m of drop, which is sufficient for it to be included in the main list of The Welsh P15s. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Caer Helen 

OS 1:50,000 map:  114

Summit Height:  33.9m (LIDAR)                                                           

Summit Grid Reference:  SH 32589 78052 (LIDAR) 

Bwlch Height:  17.4m (LIDAR) 

Bwlch Grid Reference:  SH 32770 78215 (LIDAR) 

Drop:  16.5m (LIDAR) 

 

Myrddyn Phillips (October 2021)