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

 

Craig y Bwlch (SN 718 696) 

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 Craig y Bwlch (SN 718 696)

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 Craig y Bwlch, and it is adjoined to the Carn yr Hyrddod group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with the B4340 road to its west, a minor road to its south-east and the B4343 road to its east, and has the village of Ysbyty Ystwyth 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 included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 category, with an accompanying note stating; Automatically qualified until the top was quarried away.  350c on 1986 1:50000 map. 

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

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 27m of drop, based on an estimated c 342m summit height and an estimated c 315m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the interactive mapping hosted on the WalkLakes website which has a better portrayal of contours and the height of this hill

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 Craig y Bwlch (SN 718 696)

The summit height produced by LIDAR analysis is 350.3m and is positioned at SN 71860 69685, 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 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 350.3m and this was derived from LIDAR analysis, this is 8.3m higher than the previously listed summit height of c 342m, which was based on interpolation of the uppermost 340m ring contour on the contemporary Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Carn yr Hyrddod 

Name:  Craig y Bwlch 

OS 1:50,000 map:  135, 147

Summit Height (New Height):  350.3m (LIDAR)                                                           

Summit Grid Reference:  SN 71860 69685 (LIDAR) 

Bwlch Height:  312.0m (LIDAR) 

Bwlch Grid Reference:  SN 71462 69797 (LIDAR) 

Drop:  38.3m (LIDAR) 

 

Myrddyn Phillips (October 2023)