Mapping Mountains – Hill Reclassifications – 100m Twmpau

Caer Lleiniau Uchaf (SN 521 198) – 100m Sub-Twmpau reclassified to 100m Twmpau

There has been a reclassification to the 100m Twmpau due to LIDAR analysis conducted by Myrddyn Phillips, with the criteria for this list being:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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.

When the original Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill appeared in the accompanying Hills to be surveyed sub list as it did not meet the criteria then used for the main P30 list; however this sub list has now been standardised and interpolated heights also included in the main P30 and the accompanying sub list.

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

When this list was standardised and interpolated heights also included this hill was listed with an estimated c 28m of drop, based on an estimated c 111m summit height and an estimated bwlch height of c 83m based on interpolation of 10m bwlch contouring between 80m – 90m on the Ordnance Survey 1:25,000 Explorer map.  The drop value was re-assessed when the Ordnance Survey Interactive Coverage Map became available online via the Grograph website, this mapping has contour intervals at 5m for this hill, and the drop value was again estimated to be c 28m.

The name of the bounded land where the summit of this hill is situated is Caer Lleiniau Uchaf, and this was derived from the Tithe map.  The hill is adjoined to the Mynydd Sylen group of hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and it is positioned with the B 4300 and A 40 roads, and the Afon Tywi (River Towy) to its north, and has the small community of Llanarthne towards the east north-east.

If wanting to visit the summit of the hill permission to do so should be sought as it is not a part of designated open access land, however public footpaths cross the upper part of the hill and these approach from the north, south and east.

The reclassification of Caer Lleiniau Uchaf to 100m Twmpau status is due to LIDAR analysis conducted by Myrddyn Phillips.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR image of Caer Lleiniau Uchaf

Extract from the Ordnance Surveys series of Six-Inch maps with the 372ft (113.4m) height similar in value to the LIDAR height, and with the farm named as Glan-bedw as opposed to contemporary maps where it is named Greenhill Farm

The 1m DTM LIDAR analysis gives the hill the following details:

Name:  Caer Lleiniau Uchaf

Summit Height:  113.2m

Summit Grid Reference:  SN 52155 19862

Bwlch Height:  82.0m

Bwlch Grid Reference:  SN 51657 19346

Drop:  31.2m

Therefore, the 113.2m LIDAR analysis for the summit position at SN 52155 19862 and the 82.0m LIDAR analysis for the bwlch position at SN 51657 19346 gives this hill 31.2m of drop, which is sufficient for 100m Twmpau status.

The full details for the hill are:

Group:  Mynydd Sylen

Name:  Caer Lleiniau Uchaf

OS 1:50,000 map:  159

Summit Height:  113.2m (LIDAR)

Summit Grid Reference:  SN 52155 19862 (LIDAR)

Bwlch Height:  82.0m (LIDAR)

Bwlch Grid Reference:  SN 51657 19346 (LIDAR)

Drop:  31.2m (LIDAR)

Myrddyn Phillips (October 2018)