Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

Pt. 396.4m (SH 955 525)

There has been a Significant Height Revision to a hill that is listed in the 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 initially conducted by Aled Williams and subsequently by Myrddyn Phillips.

Lidar image of Pt. 396.4m (SH 955 525)

The criteria for the list this height revision affects 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 hill is being listed by the point (Pt. 396.4m) 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 Mynydd Hiraethog 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 Alwen Reservoir to its immediate north-west, the A543 road to its west, the A5 road to its south and the B4501 road to its east, and has the village of Pentrefoelas towards the west.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the Hills to be surveyed sub list that accompanied the main P30 list, and it was listed with the summit height of c 390m.

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 c 25m of drop, based on an estimated c 393m summit height and an estimated c 368m bwlch height, with both values based on interpolation of 10m contouring 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.

The summit height produced by LIDAR analysis is 396.4m and is positioned at SH 95514 52528, this is not a dramatic height revision compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, this hill’s new listed summit height is 396.4m and this was derived from LIDAR analysis, this is 3.4m higher compared to its previously listed summit height of c 393m that was derived from interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Mynydd Hiraethog

Name:  Pt. 396.4m

OS 1:50,000 map:  116

Summit Height (New Height):  396.4m (LIDAR)

Summit Grid Reference:  SH 95514 52528 (LIDAR)

Bwlch Height: 367.5m (LIDAR)

Bwlch Grid Reference:  SH 95277 52580 (LIDAR)

Drop:  28.9m (LIDAR)

Myrddyn Phillips (August 2020)