Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

Pt. 77.7m (ST 129 775) – Lesser Dominant addition

There has been an addition to the list of Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Pt. 77.7m (ST 129 775)

The criteria for the list that this addition applies to are:

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

As I do not know an appropriate name for this hill either from historic research or local enquiry it is being listed by the point (Pt. 77.7m) notation, and it is adjoined to the Cymoedd Morgannwg group of hills, which are situated in the central part of South Wales (Region C, Sub-Region C2), and it is encircled by minor roads with the Afon Elái (Ely River) to its south, and is positioned on the edge of Fairwater which is a district in the west of the city of Caerdydd (Cardiff).

This hill was not included in the main P30 list or the accompanying Hills to be surveyed sub list when the original Welsh 30-99m P30 hills were published on Geoff Crowder’s v-g.me website, as it was considered not to meet the criteria then used for this list.  This list has now been standardised with drop values and interpolated heights also included in the main P30 and the accompanying sub list.

Extract from the Ordnance Survey 1:25,000 Explorer map showing the summit of this hill

After this list was standardised with interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 26m of drop, based on its 77m summit spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated bwlch height of c 51m based on interpolation of 5m contouring between 50m – 55m on the Ordnance Survey 1:25,000 Explorer map.  However, this mapping shows that the critical bwlch of this hill could be placed in one of two positions with the farthest position from its summit now being part of land that forms a dismantled railway cutting.   

Extract from the Ordnance Survey 1:25,000 Explorer map showing the bwlch of this hill

The details for this hill were re-examined when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals and for the majority of land comprising old mine and quarry workings, and rail and road cuttings it shows present day continuous contours, as opposed to the broken contours on the 1:25,000 Explorer map.  This map has bwlch contours for this hill between 45m – 50m but its critical bwlch could still be placed in one of two positions.

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 bwlch image of Pt. 77.7m

The confirmation of this hill’s addition to Lesser Dominant status is due to LIDAR analysis, resulting in a 77.7m summit height and a 44.4m bwlch height, with these values giving this hill 33.3m of drop and 42.82% dominance. 

The inclusion of this hill to Lesser Dominant status is dependent upon using the height of rail or road cuttings if lower on the hill to hill traverse in preference to the height and position of any natural col that may still exist. 

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Pt. 77.7m

OS 1:50,000 map:  171

Summit Grid Reference:  ST 12931 77574 (LIDAR)

Summit Height:  77.7m (LIDAR)

Bwlch Grid Reference:  ST 11808 79174 (LIDAR)

Drop Summit to Bwlch:  33.3m (LIDAR) 

Drop Bwlch to ODN:  44.4m (LIDAR)

Dominance:  42.82% (LIDAR)

Myrddyn Phillips (August 2019)