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

Hill Park (SM 955 102) – Lesser Dominant addition

There has been an addition to the list of the Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill prompted by detail produced by Joe Nuttall in his surface analysis programme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Hill Park (SM 955 102)

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, and the list is now available inits entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Hill Park, and this was derived from the Tithe map, and it is adjoined to the Garn Fawr group of hills which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads, with the A4076 road farther to its west, and the A477 road to its south-west, and has the village of Johnston towards the west.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 99m summit height, based on the spot height that appears on the contemporary 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 31m of drop, based on the 99m summit spot height and an estimated c 68m bwlch height, based on interpolation of 5m contouring between 65m – 70m, resulting with the drop value being insufficient in relation to the summit height for consideration to Lesser Dominant status. 

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.

Therefore, the addition of this hill to Lesser Dominant status is due to LIDAR analysis, resulting in a 99.5m summit height and a 63.6m bwlch height, with these values giving this hill 35.9m of drop and 36.16% dominance which is sufficient for Lesser Dominant status, with the caveat that the bwlch position has been relocated to a rail cutting which conforms with the protocols used in this list.

 

The full details for the hill are:

Group:  Garn Fawr

Name:  Hill Park

OS 1:50,000 map:  157, 158

Summit Height:  99.5m (LIDAR)

Summit Grid Reference:  SM 95585 10244 (LIDAR)

Bwlch Height:  63.6m (LIDAR)

Bwlch Grid Reference:  SM 93281 10622 (LIDAR)

Drop:  35.9m (LIDAR)

Dominance:  36.16% (LIDAR)

 

Myrddyn Phillips (January 2024)