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

Mynydd Coch (SH 804 099) - Lesser Dominant deletion

There has been a deletion from the listing 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 derived from a Trimble GeoXH 6000 summit survey conducted by Myrddyn Phillips and assisted by Graham Jackson and LIDAR bwlch analysis conducted by Myrddyn Phillips.

Mynydd Coch (SH 804 099)

The criteria for the list that this deletion 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 in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Mynydd Coch, and it is adjoined to the Aran Fawddwy group of hills, which are situated in the south-western part of North Wales (Region C1, Sub-Region C1B), and it is positioned with a minor road to its north, the A487 road to its west and the A470 to its east, and has the small community of Aberllefenni towards the west.

After the original 400m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website were standardised and interpolated heights and drop values also included, this hill was listed with 157m of drop, based on the 469m 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 the 312m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map, with these values giving this hill 33.48% dominance and its inclusion as a Lesser Dominant hill.

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

The summit of this hill was subsequently surveyed with the Trimble GeoXH 6000, resulting in a 468.3m height and when coupled with the 312m bwlch spot height these values gave this hill 156m of drop and 33.31% dominance, and therefore it was deleted from Lesser Dominant status.

The Trimble GeoXH 6000 gathering data at the summit of Mynydd Coch (SH 804 099)

However, it was not until the latest 1m LIDAR became available that the bwlch 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 Mynydd Coch

Therefore, the confirmation of the deletion of this hill from Lesser Dominant status is due to LIDAR bwlch analysis coupled with the summit height derived from the Trimble GeoXH 6000 survey, resulting in a 468.3m summit height and a 313.0m bwlch height, with these values giving this hill 155.3m of drop and 33.15% dominance, which is insufficient for Lesser Dominant status.

The full details for the hill are:

Group:  Aran Fawddwy

Name:  Mynydd Coch

Previously Listed Name:  Mynydd Cwmcelli 

OS 1:50,000 map:  124, 125

Summit Height:  468.3m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 80458 09952 (Trimble GeoXH 6000) 

 

Bwlch Height:  313.0m (LIDAR)

Bwlch Grid Reference:  SH 81012 10795 (LIDAR)

Drop:  155.3m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  33.15% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips (October 2016)