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

 

Moel Hafod yr Ŵyn (SH 841 322) 

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 derived from LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips. 

LIDAR image of Moel Hafod yr Ŵyn (SH 841 322)

The criteria for the list that this height revision 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, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022.

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Moel Hafod yr Ŵyn, and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor road to its south-west and east, and has the village of Llanuwchllyn towards the south-east. 

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a 389m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, with the caveat that the uppermost 390m ring contour had been missed. 

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

After the accompanying 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 37m of drop, based on the 396m summit spot height that appears on the Harvey 1:40,000 Snowdonia South British Mountain Map and the 359m 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. 

Extract from the Harvey 1:40,000 Snowdonia South British Mountain 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 of Moel Hafod yr Ŵyn (SH 841 322)

LIDAR analysis gives the summit height of this hill as 398.2m and this comes 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, Harvey or other interactive 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 with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 398.2m and this was derived from LIDAR analysis, this is 9.2m higher than the originally listed summit height of 389m which appears as a spot height on the contemporary Ordnance Survey 1:25,000 Explorer map and 2.2m higher than the 396m summit spot height that appears on the Harvey 1:40,000 Snowdonia South British Mountain Map. 

 

The full details for the hill are: 

Group:  Arenig Fawr 

Name:  Moel Hafod yr Ŵyn 

OS 1:50,000 map:  124, 125

Summit Height (New Height):  398.2m (LIDAR)                                                           

Summit Grid Reference:  SH 84199 32238 (LIDAR) 

Bwlch Height:  358.4m (LIDAR) 

Bwlch Grid Reference:  SH 84033 32465 (LIDAR) 

Drop:  39.8m (LIDAR) 

 

Myrddyn Phillips (December 2021)