Mapping Mountains – Hill Reclassifications – 200m Twmpau

Penmaen Bach (SH 750 777) – 200m Sub-Twmpau addition

There has been confirmation of an addition to the 200m Twmpau list, with the summit height and its location, the drop and status of the hill initially confirmed by LIDAR analysis and subsequently by a survey with the Trimble GeoXH 6000 which were conducted by Myrddyn Phillips, with the latter taking place on the 15^th October 2018.

Penmaen Bach (SH 750 777)

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

The name of the hill is Penmaen Bach and it is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A55 road and the coast to its north, and has the town of Conwy towards the east.

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 Hills to be surveyed sub list as it did not meet the criteria then used in this list, however this sub list has now been standardised and interpolated heights and drop values also included in the main P30 and the accompanying sub list.

After this list was standardised and interpolated heights also included the details for the hill were re-assessed when the Ordnance Survey Vector Map Local became available online, this map is hosted on the Geograph website and is entitled the Interactive Coverage Map.

The Ordnance Survey Vector Map Local hosted on the Geograph website which is entitled the Interactive Coverage Map

When the details for this hill were re-assessed it was listed with an estimated c 23m of drop, based on an estimated c 236m summit height and an estimated c 213m bwlch height, with each based on interpolation of 5m contouring on the Ordnance Survey Vector Map Local.

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 Penmaen Bach

The confirmation of the addition of Penmaen Bach to 200m Sub-Twmpau status is due to LIDAR analysis and a subsequent survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, resulting in a 235.4m summit height and a 208.3m bwlch height, with these values giving this hill 27.1m of drop which is sufficient for it to be classified as a 200m Sub-Twmpau.

The Trimble GeoXH 6000 gathering data at the summit of Penmaen Bach

 

The Trimble GeoXH 6000 gathering data at the bwlch of Penmaen Bach

The full details for the hill are:

Group:  Carneddau

Name:  Penmaen Bach

OS 1:50,000 map:  115

Summit Height:  235.4m (converted to OSGM15)

Summit Grid Reference:  SH 75005 77770

Bwlch Height:  208.3m (converted to OSGM15)

Bwlch Grid Reference:  SH 74888 77897

 

Drop:  27.1m

For details on the survey of this hill

Myrddyn Phillips (April 2019)