Mapping Mountains – Hill Reclassifications – 200m Twmpau

Y Ceiliog Mawr (SH 594 598) - 200m Twmpau addition

There has been an addition of a hill to the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips.

Y Ceiliog Mawr (SH 594 598).  Photo: Aled Williams

The hill was first proposed as a prospective P30 approximately two years ago by Aled Williams and it then waited to be Trimbled, but as it looked a daunting prospect the Trimble surveyor shied away from his duties.  In the interim LIDAR became available.

The criteria for the list that this addition 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.

200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Y Ceiliog Mawr, and it is adjoined to the Glyder Fawr group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with Llyn Peris and the A4086 road to its south-west, and has the town of Llanbertis towards the west.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the main P30 list or the accompanying Hills to be surveyed sub list, as with no significant contours of note on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map it was difficult to know whether any hill of note existed.

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

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. 

LIDAR image of Y Ceiliog Mawr (SH 594 598)

Therefore, the addition of this hill to 200m Twmpau status is due to LIDAR analysis, resulting in a 220.5m summit height and a 182.3m bwlch height, with these values giving this hill 38.2m of drop, which is sufficient for it to be classified as a 200m Twmpau.

The full details for the hill are: 

Group:  Glyder Fawr 

Name:  Y Ceiliog Fawr 

OS 1:50,000 map:  115

Summit Height:  220.5m (LIDAR) 

Summit Grid Reference:  SH 59467 59848 (LIDAR) 

Bwlch Height:  182.3m (LIDAR) 

Bwlch Grid Reference:  SH 59529 59826 (LIDAR) 

Drop:  38.2m (LIDAR) 

My thanks to Aled Williams for supplying the details of his LIDAR analysis of this hill.

To view an old and a relatively recent photograph of Y Ceiliog Mawr {here} {here}

Myrddyn Phillips (December 2016)