Mapping Mountains – Hill Reclassifications – 200m Twmpau

 

Ffridd (SN 808 977) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been confirmation of a reclassification to the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Ffridd (SN 808 977)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Ffridd and this was derived from the Tithe map, and it is adjoined to the Pumlumon group of hills, which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is encircled by minor roads and tracks with the B4518 road further to the east, the A470 road further to the north-east, the A489 road further to the north-west and the A487 road further to the west, and has the town of Machynlleth towards the north-west. 

When the original 200m 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 that accompanied the main P30 list, as it was considered not to meet the criteria then used for the main P30 category. 

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 33m of drop, based on an estimated c 236m summit height and an estimated c 233m bwlch height, with each height based on interpolation from 10m contouring on the Ordnance Survey 1:25,000 Explorer map. 

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

Since publication of these P30 lists on 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 Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map.  This mapping had many spot heights not on other publicly available Ordnance Survey maps, and for this hill it showed a 237m spot height on the area of its summit. 

Another resource available online is the interactive mapping originated from Ordnance Survey data hosted on the Magic Maps website.  This mapping also shows a 237m spot height on the summit area of this hill. 

Extract from the Magic Maps website

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 confirmation of the reclassification of this hill from 200m Sub-Twmpau status is due to LIDAR analysis, resulting in a 236.6m summit height and a 202.5m bwlch height, with these values giving this hill 34.1m of drop, which is sufficient for it to be classified as a 200m Twmpau. 

 

The full details for the hill are: 

Group:  Pumlumon 

Name:  Ffridd 

OS 1:50,000 map:  135, 136

Summit Height:  236.6m (LIDAR) 

Summit Grid Reference:  SN 80899 97705 (LIDAR) 

Bwlch Height:  202.5m (LIDAR) 

Bwlch Grid Reference:  SN 81383 97749 (LIDAR) 

Drop:  34.1m (LIDAR) 

 

Myrddyn Phillips (March 2021)