Mapping Mountains – Summit Relocations – 200m Twmpau and Y Trechol – The Dominant Hills of Wales

Mynydd Gelliwastad (SN 678 015)

There has been a Summit Relocation to a hill that is listed in the 200m Twmapu and Y Trechol – The Dominant Hills of Wales, with the summit height, drop and status of the hill being confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Mynydd Gelliwastad

The criteria for the two lists that this summit relocation applies to are:

200m Twmpau - Welsh hills at or above 200m and below 300m in height with 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

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.

The name of the hill is Mynydd Gelliwastad, and it is adjoined to the Mynydd Penlle’rcastell group of hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and has the Lower Clydach River, the B 4603 and the A 4067 towards its east and the M 4 towards its south, and has the village of Clydach towards its east.

As the summit of the hill is a part of designated open access land it can be approached from most directions with public footpaths accessing this land from the north and the west.

Prior to LIDAR analysis this hill was listed with c 100m of drop based on the 213m height given to a triangulation pillar positioned at SN 67799 01456 that appears on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and an estimated bwlch height of c 113m based on interpolation of 5m contours between 110m – 115m.

Close up LIDAR image of the summit of Mynydd Gelliwastad

LIDAR image of the bwlch of Mynydd Gelliwastad

The summit height produced by LIDAR analysis is 213.9m at SS 67852 01598 and its position in relation to that previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

Extract from the Ordnance Survey 1:25,000 Explorer map showing the new summit position in relation to the old listed summit position at the trig pillar

The summit height produced by LIDAR analysis is 213.9m and is positioned at SN 67852 01598, this position is not given a spot height on contemporary Ordnance Survey maps but appears within an uppermost 210m contour ring.  This position is approximately 100 metres north from where the previously listed summit is positioned.  

 

The full details for the hill are:

Group:  Mynydd Penlle’rcastell

Name:  Mynydd Gelliwastad

OS 1:50,000 map:  159

Summit Height:  213.9m (LIDAR)

Summit Grid Reference (new position):  SN 67852 01598 (LIDAR)

Bwlch Height:  114.8m (LIDAR)

Bwlch Grid Reference:  SN 67677 02435 (LIDAR) 

 

Drop:  99.1m (LIDAR)

Dominance:  46.33% (LIDAR)

Myrddyn Phillips (January 2019)