Mapping Mountains – Summit Relocations – 100m Twmpau

 

Banc (SN 568 757) 

There has been a Summit Relocation to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Banc (SN 568 757)

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

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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. 

The 100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Banc and this was derived from the Tithe map, and it is adjoined to the Elenydd group of hills which are situated in the western part of Mid and West Wales (Region B, Sub-Region B2), and it has the coast to its west and the A487 road to its east, and has the village of Llanfarian towards the north-east. 

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 192m summit height based on the spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 56695 75938. 

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

The details for this hill were subsequently re-assessed against a number of Ordnance Survey maps made available online, including the Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, the interactive mapping available on the WalkLakes website as well as the Magic Maps website and none showed further detail other than the 192m spot height adjoined to the triangulation pillar. 

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 image of Banc (SN 568 757)

The summit of this hill has now been surveyed with the Trimble GeoXH 6000 and this is being prioritised in preference to the LIDAR height and position, resulting in 194.2m at SN 56817 75750 and this height and its position comes within the parameters of the Summit Relocations used within this page heading, these parameters are: 

The term Summit Relocations applies when the hill’s high point is found to be positioned; in a different field, to a different feature such as in a conifer plantation, placed within a different map contour, to a different point where a number of potential summit positions are within close proximity, or when natural ground or 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, 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. 

The Trimble GeoXH 6000 gathering data at the summit of Banc with the previously listed summit in the background

Therefore, the new listed summit height for this hill is 194.2m and is positioned at SN 56817 75750, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and is approximately 200 metres south-eastward from where the summit was originally listed which was to the position of the 192m spot height adjoined to the triangulation pillar. 

 

The full details for the hill are:

Group:  Elenydd 

Name:  Banc

OS 1:50,000 map:  135

Summit Height:  194.2m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference (New Position):  SN 56817 75750 (Trimble GeoXH 6000)

Bwlch Height:  130.2m (LIDAR)

Bwlch Grid Reference:  SN 57845 73062 (LIDAR) 

Drop:  64.0m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (March 2021)