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

Hafod Llŷn (SN 625 700) – Sub-Trichant reclassified to Trichant

There has been a reclassification 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 and a subsequent Trimble GeoXH 6000 survey.

LIDAR image of Hafod Llŷn (SN 625 700)

This was initiated by Joe Nuttall who produced a summit analysis programme that used LIDAR with an alternative height map (DEM) allowing identification of summits and cols and thereby drops.  The resulting spreadsheet that Joe produced contains over 29,600 hills.

This spreadsheet is being evaluated by a number of people, and for this particular hill it was Jim Bloomer who initially assessed the data on the spreadsheet produced for this hill against that produced via LIDAR.

Myrddyn Phillips then evaluated the details for this hill via LIDAR analysis and confirmed its height and drop and hence its reclassification to Trichant status.

The criteria for the list that this reclassification 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 13th May 2017.

The name the hill is now listed by is Hafod Llŷn and this was derived from the Tithe map and local enquiry, and it is adjoined to the Hafod Ithel group of hills, which are situated in the western part of Mid and West Wales (Region B, Sub-Region B3), and it is encircled by minor roads and farther afield it has the B4576 road to its west and the A485 road to its east, and has the village of Lledrod towards the 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 Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the accompanying main P30 list.

When 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 27m of drop based on the 330m summit spot height and an estimated c 303m bwlch height, with the latter based on interpolation of 10m contouring between 300m – 310m that appear on the Ordnance Survey 1:50,000 Landranger and 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.

LIDAR summit image for Hafod Llŷn

LIDAR bwlch image for Hafod Llŷn

The result produced by LIDAR analysis gives this hill a 330.7m summit height, and as the summit has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes.

The Trimble GeoXH 6000 gathering data at the summit of Hafod Llŷn

Therefore, the reclassification of this hill from Sub-Trichant status is due to LIDAR analysis and a subsequent Trimble GeoXH 6000 survey, resulting in a 330.6m summit height and a 300.0m bwlch height, with these values giving this hill 30.6m of drop, which is sufficient for it to be classified as a Trichant.

The full details for the hill are:

Group:  Hafod Ithel

Name:  Hafod Llŷn

OS 1:50,000 map:  135

Summit Height:  330.6m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 62592 70023 (Trimble GeoXH 6000)

Bwlch Height:  300.0m (LIDAR)

Bwlch Grid Reference:  SN 62234 69672 & SN 62235 69675 (LIDAR)

Drop:  30.6m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips (September 2020)