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

Cefn Ucaf (SJ 012 461)

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 conducted by Myrddyn Phillips.

LIDAR image of Cefn Uchaf (SJ 012 461)

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 name the hill is listed by is Cefn Uchaf and this was derived from the Tithe map, 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 B5105 road to its north, the A5 road to its south and the A494 road to its east, and has the town of Corwen towards the east 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 not included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for this sub category. 

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 2om of drop, based on the 337m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 317m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage 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 Cefn Uchaf

The summit height produced by LIDAR analysis is 340.0m and is positioned at SJ 01294 46112, 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 340.0m and this was derived from LIDAR analysis, this is 3.0m higher compared to its previously listed summit height of 337m that was derived from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Mynydd Hiraethog

Name:  Cefn Uchaf

OS 1:50,000 map:  116

Summit Height (New Height):  340.0m (LIDAR)

Summit Grid Reference:  SJ 01294 46112 (LIDAR)

Bwlch Height: 319.1m (LIDAR)

Bwlch Grid Reference:  SJ 00949 46115 (LIDAR)

Drop:  20.9m (LIDAR)

Myrddyn Phillips (August 2020)