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

Caer Drewyn (SJ 091 444) – Trichant addition

There has been an addition 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 confirmed by LIDAR analysis conducted by Myrddyn Phillips, with a subsequent Leica GS15 survey conducted by John Barnard and Graham Jackson. 

Caer Drewyn (SJ 091 444)

The criteria for the list that this addition 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 now listed by is Caer Drewyn, and this was derived from local enquiry by Aled Williams, and it is adjoined to the Moel y Gamelin group of hills, which are situated in the north-eastern part of North Wales (Region A, Sub-Region A2), and it is positioned with the A5104 road to its north, the B5437 road to its south and the B5436 road to its east, and has the village of Carrog towards the east south-east. 

When the original 300m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list and given twin topped 314m map heighted summit status along with its adjacent hill positioned at SJ 094 443. 

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

After the P30 lists were standardised and interpolated heights and drop values also included, this hill was listed as the non-priority summit with 18m of drop based on the 314m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 296m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, with its adjacent 314m twin summit given priority status and listed with an estimated c 91m of drop based on the 314m summit spot height and an estimated c 223m bwlch height based on interpolation of 10m contouring between 220m – 230m that appear on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

However, it was not until LIDAR became available that the details for these two summits 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 gives the following detail for each summit: 

313.0m positioned at SJ 09438 44364. 

313.1m positioned at SJ 09125 44411.

 

The summit of these two hills have now been surveyed by the Leica GS15 and it is this result that is being prioritised for this hill.

Therefore, the addition of this hill to Trichant status is due to LIDAR analysis and a subsequent Leica GS15 survey, resulting in a 313.5m summit height and a 222.7m bwlch height, with these values giving this hill 90.8m of drop, which is sufficient for it to be classified as a Trichant. 

 

The full details for the hill are: 

Group:  Moel y Gamelin 

Name:  Caer Drewyn 

OS 1:50,000 map:  125

Summit Height:  313.5m (Leica GS15)                                                           

Summit Grid Reference:  SJ 09127 44416 (Leica GS15) 

Bwlch Height:  222.7m (LIDAR) 

Bwlch Grid Reference:  SJ 09770 45600 (LIDAR) 

Drop:  90.8m (Leica GS15 summit and LIDAR bwlch) 

 

Myrddyn Phillips (March 2021)