Mapping Mountains – Hill Reclassifications – Y Trichant – The 300m Hills of Wales

 

Ciliau (SN 951 542) – Trichant reclassified to Sub-Trichant 

There has been a reclassification to the list of Y Trichant – The 300m Hills of Wales, 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 Ciliau (SN 951 542)

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

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Ciliau and it is adjoined to the Elenydd group of hills, which are situated in the central part of the Mid and West Wales Region (Region B, Sub-Region B2), and it is positioned with minor roads to its north and west, and the B4358 road to its south-east, and has the village of Beulah towards the south-west. 

When the original 300m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 category. 

When the sub list was standardised and interpolated heights and drop values also included, the details for this hill were re-evaluated and it was listed with an estimated c 33m of drop, based on the 377m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and the 1:25,000 Explorer map and an estimated c 344m bwlch height based on interpolation of 10m contouring between 340m – 350m that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

Since publication of the P30 lists of Geoff Crowder’s v-g.me website there have been a number of Ordnance Survey maps made available online, some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website, whilst others are current and digitally updated such as the old Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available maps and for this hill it had a 347m bwlch spot height positioned at SN 94905 54722, and when coupled with the 377m summit spot height gave this hill 30m of drop. 

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 reclassification of this hill to Sub-Trichant status is due to LIDAR analysis, resulting in a 376.1m summit height and a 346.3m bwlch height, with these values giving this hill 29.8m of drop, which is insufficient for it to be classified as a Trichant. 

 

The full details for the hill are: 

Group:  Elenydd 

Name:  Ciliau 

OS 1:50,000 map:  147

Summit Height:  376.1m (LIDAR)                                                           

Summit Grid Reference:  SN 95121 54281 (LIDAR) 

Bwlch Height:  346.3m (LIDAR) 

Bwlch Grid Reference:  SN 94897 54729 (LIDAR) 

Drop:  29.8m (LIDAR) 

 

Myrddyn Phillips (September 2021)