Mapping Mountains – Summit Relocations – 100m Twmpau

 

Banc Uchaf (SN 617 743) 

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 derived from LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Banc Uchaf (SN 617 743)

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 Uchaf 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 is positioned with the A485 road to its north and minor roads to its west, south and east, and has the village of Llanilar towards the north 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 197m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at SN 61731 74185. 

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. 

LIDAR summit image of Banc Uchaf

LIDAR analysis indicated a summit relocation for this hill and as the summit has subsequently been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes, resulting in a summit height of 197.6m positioned at SN 61768 74325 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 Uchaf

Therefore, the new listed summit height for this hill is 197.6m and is positioned at SN 61768 74325, 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 140 metres northward from where the summit was originally listed which was to the position of the 197m spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Elenydd 

Name:  Banc Uchaf

OS 1:50,000 map:  135

Summit Height:  197.6m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference (New Position):  SN 61768 74325 (Trimble GeoXH 6000)

Bwlch Height:  148.5m (LIDAR)

Bwlch Grid Reference:  SN 61371 72717 (LIDAR) 

Drop:  49.1m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (May 2021)