Mapping Mountains – Summit Relocations – Y Trichant

Cefn Llanbister (SO 116 733)

There has been a Summit Relocation to a hill that is listed in the Y Trichant, and which was initiated by LIDAR analysis and confirmed by a survey with the Trimble GeoXH 6000, both of which were conducted by Myrddyn Phillips, with the latter taking place on the 03.07.18 in warm and clear conditions.

Cefn Llanbister (SO 116 733)

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

Y Trichant – Welsh hills at or above 300m and below 400m in height with 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 its renaming appearing on Mapping Mountains on the 13^th May 2017.

The name of the hill is Cefn Llanbister and it is placed in the Beacon Hill group of hills, which are situated in the north-eastern part of Mid and West Wales (Region B, Sub-Region B1), and it is positioned with the Afon Ieithon (River Ithon) and the A 483 road to its west and the B 4356 road to its north, and has the small community of Llanbister at its base to the west of the summit.

As the summit of the hill is a part of open access land it can be approached from most directions with public footpaths accessing this land from the west and east, with the most convenient access to the hill via a track that leaves the B 4356 road just to the north of the summit.

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 373m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating 376m at SO GR117732 on 1986 1:50000 map.

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

Prior to LIDAR analysis and the subsequent survey with the Trimble GeoXH 6000 the listed height of this hill had been revised to 376m based on the spot height on the Ordnance Survey 1:50,000 Landranger map.

Extract from the Ordnance Survey 1:50,000 Landranger map

The summit height produced by the Trimble GeoXH 6000 survey is 377.5m (converted to OSGM15) at SO 11690 73303 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.

The summit height produced by the Trimble GeoXH 6000 survey is 377.5m (converted to OSGM15) and is positioned at SO 11690 73303, this position is not given a spot height on contemporary Ordnance Survey maps and is approximately 100 metres east from where the 376m spot height appears on the Ordnance Survey 1:50,000 Landranger map and 450 metres north-west from where the 373m spot height appears on the Ordnance Survey 1:25,000 Explorer map.   

The Trimble GeoXH 6000 gathering data at the summit of Cefn Llanbister which confirmed the summit relocation of this hill

The full details for the hill are:

Group:  Beacon Hill

Name:  Cefn Llanbister

OS 1:50,000 map:  136, 148

Summit Height:  377.5m (converted OSGM15)

Summit Grid Reference (new position):  SO 11690 73303

Bwlch Height:  335.3m (converted to OSGM15)

Bwlch Grid Reference:  SO 12399 74601 

 

Drop:  42.2m (converted to OSGM15)

For details on the survey that relocated the summit position of this hill

Myrddyn Phillips (November 2018)