Mapping Mountains – Hill Reclassifications – 30–99m Twmpau

Daufraich (SM 661 236) - Double Sub-Twmpau addition

There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height and its location, the drop and status of the hill derived from a Trimble GeoXH 6000 survey and LIDAR analysis conducted by Myrddyn Phillips.

Daufraich (SM 661 236)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Daufraich, and it is adjoined to the Garn Fawr group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned on an island with a minor road over 7.00km to its east, and has the small city of Tyddewi (St David's) towards the east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.  

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

After 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 21m of drop, based on the twin 21m summit spot heights positioned at SM 66198 23680 and SM 66173 23699 that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

However, it was not until the survey with the Trimble GeoXH 6000 and subsequent LIDAR analysis 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.

Gathering data at the summit of Daufraich (SM 661 236)

Therefore, the confirmation of the addition of this hill to Double Sub-Twmpau status is due to a Trimble GeoXH 6000 survey, resulting in a 21.7m summit height and therefore also drop, which is sufficient for it to be classified as a Double Sub-Twmpau.  

The full details for the hill are:

Group:  Garn Fawr

Name:  Daufraich

OS 1:50,000 map:  157

Summit Height:  21.7m (converted to OSGM15)

Summit Grid Reference:  SM 66199 23673

Bwlch Height:  N/A (island)

Bwlch Grid Reference:  N/A (island)

Drop:  21.7m 

Myrddyn Phillips (May 2016)