Mapping Mountains – Hill Reclassifications – 100m Twmpau

Warren Wood (SN 600 190) – 100m Twmpau reclassified to 100m Sub-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 was included in the main P30 list.  When the accompanying sub list was standardised, and interpolated heights also included this hill was listed with an estimated c 31m of drop, based on an estimated c 190m summit height and an estimated bwlch height of c 159m based on interpolation of 10m bwlch contouring between 150m – 160m 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 31m.

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

The name of the hill is Warren Wood and it 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 road to the north, the A 476 road to the east, and has the town of Llandeilo towards the 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, for those wishing to do so the easiest access is from a minor road to the west and south.

The reclassification of Warren Wood to 100m Sub- 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 summit image of Warren Wood

LIDAR bwlch image of Warren Wood

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

Name:  Warren Wood

Summit Height:  189.4m

Summit Grid Reference:  SN 60037 19085

Bwlch Height:  160.4m

Bwlch Grid Reference:  SN 59229 18910

Drop:  28.95m

Therefore, the 189.4m LIDAR analysis for the summit position at SN 60037 19085 and the 160.4m LIDAR analysis for the bwlch position at SN 59229 18910 gives this hill 28.95m of drop, which is insufficient for continued 100m Twmpau status.

The full details for the hill are:

Group:  Mynydd Sylen

Name:  Warren Wood

OS 1:50,000 map:  159

Summit Height:  189.4m (LIDAR)

Summit Grid Reference:  SN 60037 19085 (LIDAR)

Bwlch Height:  160.4m (LIDAR)

Bwlch Grid Reference:  SN 59229 18910 (LIDAR)

Drop:  28.95m (LIDAR)

Myrddyn Phillips (October 2018)