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

 

Bryn Dinas (SN 646 999) – Trichant reclassified to Sub-Trichant

There has been confirmation of 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 a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

Bryn Dinas (SN 646 999)

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, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

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

The name the hill is listed by is Bryn Dinas and it is adjoined to the Tarren y Gesail group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with a minor road to its south and the A493 road to its west and farther south, and has the town of Tywyn towards the west. 

When the original 300m height band of Welsh P30 hills were 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. 

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

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 30m of drop, based on the 346m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 316m bwlch height, based on interpolation of 10m contouring between 310m – 320m.  The estimated c 316m bwlch height was based on the 317m spot height that appears adjoined to a cairn on the Ordnance Survey 1:50,000 Landranger map.  If this height was taken to the top of the cairn, ground at its base would be approximately c 316m in height. 

Extract from the Ordnance Survey 1:50,000 Landranger map

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of 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 were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites. 

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 Ordnance Survey maps and for this hill it had a 318m spot height on the area of the bwlch positioned on a track at SN 64653 00072. 

One of the resources recently available online is the mapping on the OS Maps website and the details for this hill were subsequently re-assessed against this mapping.  This is the replacement for OS Get-a-map and until recent times had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000 Explorer map and used to appear on the online Vector Map Local.  This mapping had bwlch contouring between 315m – 320m, with interpolation placing the height of the bwlch as an estimated c 317m, and when coupled with the 318m spot height on the Interactive Coverage Map it was decided to amend the drop value for this hill to an estimated c 29m. 

Gathering data at the bwlch of Bryn Dinas

Gathering data at the summit of Bryn Dinas

Therefore, the confirmation of the reclassification of this hill to Sub-Trichant status is due to a Trimble GeoXH 6000 survey, resulting in a 345.6m summit height and a 315.8m 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:  Tarren y Gesail 

Name:  Bryn Dinas 

OS 1:50,000 map:  135

Summit Height:  345.6m (converted to OSGM15)                                                           

Summit Grid Reference:  SN 64662 99930 

Bwlch Height:  315.8m (converted to OSGM15) 

Bwlch Grid Reference:  SH 64694 00067 

Drop:  29.8m 

 

Myrddyn Phillips (March 2022)