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

Waun Llwyd (SJ 003 165) 

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 conducted by Myrddyn Phillips. 

LIDAR image of Waun Llwyd (SJ 003 165)

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 therenaming 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 Waun Llwyd and this was derived from the Tithe map, and it is adjoined to the Esgeiriau Gwynion group of hills, which are situated in the southern part of North Wales (Region A, Sub-Region A3), and it is positioned with a minor road to its north and east, and has the village of Llanwddyn towards the north-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After 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 20m of drop, based on an estimated c 363m summit height and an estimated c 343m bwlch height, with both heights based on interpolation of 10m contouring that appear 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. 

LIDAR summit image of Waun Llwyd (SJ 003 165)

LIDAR analysis gives the summit height of this hill as 367.4m 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 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, the new listed summit height of this hill is 367.4m and this was derived from LIDAR analysis, this is 4.4m higher than the previously listed summit height of c 363m, which was based on interpolation of 10m contouring that appear on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are: 

Group:  Esgeiriau Gwynion 

Name:  Waun Llwyd 

OS 1:50,000 map:  125

Summit Height (New Height):  367.4m (LIDAR)                                                           

Summit Grid Reference:  SJ 00323 16521 (LIDAR) 

Bwlch Height:  345.2m (LIDAR) 

Bwlch Grid Reference:  SJ 00193 16719 (LIDAR) 

Drop:  22.2m (LIDAR) 

 

Myrddyn Phillips (June 2022)