Mapping Mountains – Summit Relocations – 200m Twmpau

Banc (SN 638 606) 

There has been a Summit Relocation to a hill that is listed in the 200m 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 (SN 638 606)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 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. 

The 200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Banc 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 and the B4577 road to its north-west, a minor road and the B4576 road to its west, a minor road and the B4342 road to its south and the B4578 road to its east, and has the town of Tregaron towards the east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a summit height of 247m 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 636 602. 

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 (SN 638 606)

The height produced by LIDAR analysis to the summit of this hill is 247.5m positioned at SN 63875 60609, and this position in relation to that of the triangulation pillar 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 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 summit height produced by LIDAR analysis is 247.5m which is positioned at SN 63875 60609, 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 400 metres north-eastward from where the previously listed summit is positioned. 

 

The full details for the hill are:

Group:  Mynydd Bach 

Name:  Banc 

OS 1:50,000 map:  146

Summit Height:  247.5m (LIDAR) 

Summit Grid Reference (New Position):  SN 63875 60609 (LIDAR) 

Bwlch Height:  184.8m (LIDAR) 

Bwlch Grid Reference:  SN 65417 60139 & SN 65423 60135 (LIDAR) 

Drop:  62.6m (LIDAR)

 

Myrddyn Phillips (October 2022)