Friday, 19 June 2020

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

Cae Scybo(ST 400 985) – 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 confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Cae Scybor (ST 400 985)

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 3rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

The name the hill is listed by is Cae Seybôr and this was derived from the Tithe map and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is encircled by minor roads with the A449 road and the Afon Wysg (River Usk) further to the west, and has the town of Brynbuga (Usk) towards the north-west.

When the original 100m height band of Welsh P30 hills published on Geoff Crowder’s website were standardised and interpolated heights also included, this hill was listed with c 43m of drop, based on the 125m summit spot height and a c 82m bwlch height, with the latter height estimated from interpolation of 5m contouring that along with the summit spot height appears on the Ordnance Survey 1:25,000 Explorer map.

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and although no additional information is shown on this mapping, it was at this time that the interpolated bwlch height was amended to c 83m, and when coupled with the 125m summit height these values give this hill c 42m drop and 33.60% dominance.

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. 

Therefore, the deletion of this hill from Lesser Dominant status is due to LIDAR analysis, resulting in a 125.5m summit height and an 83.7m bwlch height, with these values giving this hill 41.8m of drop and 33.29% of dominance, which is insufficient for it to be classified as a Lesser Dominant hill.

The full details for the hill are:

Group:  Gwent Is Coed

Name:  Cae Scybor

OS 1:50,000 map:  171

Summit Grid Reference:  ST 40051 98581 (LIDAR)

Summit Height:  125.5m (LIDAR)

Bwlch Grid Reference:  ST 40255 98479 (LIDAR)

Drop Summit to Bwlch:  41.8m (LIDAR)

Drop Bwlch to ODN:  83.7m (LIDAR)

Dominance:  33.29% (LIDAR)

Myrddyn Phillips (June 2020)

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