Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

Banc (SN 568 757) – Lesser Dominant deletion

There has been a deletion to the listing of Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Banc (SN 568 757)

The criteria for the list that this deletion applies to are: 

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales 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. 

After the original 100m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website were standardised and interpolated heights also included, this hill was listed with an estimated c 64m of drop and 33.33% dominance, based on the 192m summit spot height adjoined to a triangulation pillar positioned at SN 56695 75938 and an estimated c 126m bwlch height, based on interpolation of 10m contouring between 120m – 130m that appears on the Ordnance Survey 1:25,000 Explorer map. 

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 568 757)

LIDAR analysis relocated the summit of this hill and decreased its dominance to 33.06%, and as the summit of this hill has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised in preference to the LIDAR height and position, resulting in a summit height of 194.2m positioned at SN 56817 75750. 

The Trimble GeoXH 6000 gathering data at the summit of Banc

Therefore, the deletion of this hill from Lesser Dominant status is due to LIDAR bwlch analysis and a Trimble GeoXH 6000 summit survey, resulting in a 194.2m summit height and a 130.2m bwlch height, with these values giving this hill 64.0m of drop and 32.93% dominance, which is insufficient for it to be classified as a Lesser Dominant hill. 

 

The full details for the hill are:

Group:  Elenydd

Name:  Banc 

OS 1:50,000 map:  135

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

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

Bwlch Grid Reference:  SN 57845 73062 (LIDAR)

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

Drop Bwlch to ODN:  130.2m (LIDAR)

Dominance:  32.93% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (May 2021)