THIS HILL HAS SUBSEQUENTLY BEEN RECLASSIFIED TO TRICHANT STATUS
Dorth Siwgr (SN 834 427) – 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 detail on
contemporary maps produced from Ordnance Survey data.
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 13th May 2017, and the Introduction to the Mapping Mountains
publication of the list appearing on the 1st January 2022.
 |
| Y Trichant - The 300m Hills of Wales by Myrddyn Phillips |
The name the hill is now listed by is Dorth Siwgr and this was derived from online sources, and it is adjoined
to the Mynydd Epynt group of hills, which are situated in the central part of South Wales (Region B,
Sub-Region B1), and it is positioned with the
A483 road to its north-west and a minor road to its south, and has the town of
Llanymddyfri (Llandovery) towards the south-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.
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 27m of drop, based on an
estimated c 323m summit height and an estimated c 296m bwlch height, with both
heights based on interpolation of 10m contouring that appear on the Ordnance
Survey 1:25,000 Explorer map.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer 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 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 326m summit spot height and when coupled with the c 296m estimated bwlch height; these values gave this hill an estimated c 30m of drop. The 326m summit spot height also appears on the interactive mapping available on the Magic Maps website.
 |
| Extract from the Magic Maps website |
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 295m – 300m, with interpolation placing the height of the bwlch as an estimated c 297m.
 |
| Extract from the OS Maps website |
Therefore, the reclassification of this hill to
Sub-Trichant status is due to detail on contemporary maps produced from
Ordnance Survey data, resulting in a 326m summit height and an estimated c 297m
bwlch height, with these values giving this hill an estimated c 29m of drop,
which is insufficient for it to be classified as a Trichant.
The full details for the
hill are:
Group: Mynydd Epynt
Name: Dorth Siwgr
OS 1:50,000 map: 147,
160
Summit Height: 326m (spot height)
Summit Grid
Reference: SN 83481 42793 (hand-held GPS
via DoBIH)
Bwlch Height: c 297m (interpolation)
Bwlch Grid
Reference: SN 83712 42859 (interpolation)
Drop: c 29m (spot height summit and interpolated
bwlch)
Myrddyn Phillips
(February 2022)