Mapping Mountains – Summit Relocations – 100m Twmpau

Banc Uchaf (SN 526 471) 

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 conducted by Myrddyn Phillips. 

LIDAR image of Banc Uchaf (SN 526 471)

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 that have 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 listed by is Banc Uchaf and this was derived from the Tithe map, and it is adjoined to the Mynydd Bach group of hills, which are situated in the western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north and west, the A475 road to its south and the B4337 road to its north-east, and has the town of Llanbedr Pont Steffan (Lampeter) towards the east.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a c 180m summit height, based on the highest and largest ring contour that is positioned at SN 526 471 and appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating; Two points same height – other at SN 514 472. 

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 analysis gives the highest ground on this hill as 184.0m positioned at SN 52613 47184.  However, this is a part of a raised copse field boundary and protocols dictate that as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill. 

LIDAR summit image of Banc Uchaf (SN 526 471)

The height produced by LIDAR analysis to the natural summit of this hill is 183.9m and is positioned at SN 52615 47176, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to when the high point of the hill is positioned in a different field, to a different feature such as a conifer plantation, within a different map contour, a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered 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.

Therefore, the height produced by LIDAR analysis to the natural summit of this hill is 183.9m and is positioned at SN 52615 47176, 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 8 metres southward from where the high point of the raised copse field boundary is positioned.

 

The full details for the hill are: 

Group:  Mynydd Bach 

Name:  Banc Uchaf 

OS 1:50,000 map:  146

Summit Height:  183.9m (LIDAR) 

Summit Grid Reference (New Position):  SN 52615 47176 (LIDAR) 

Bwlch Height:  150.95m (LIDAR) 

Bwlch Grid Reference:  SN 51628 47512 (LIDAR) 

Drop:  33.0m (LIDAR) 

 

Myrddyn Phillips (January 2023)