Mapping Mountains – Hill Reclassifications – 800m Twmpau / 700m Twmpau

Pen y Gadair Fawr (SO 229 287) – 800m Twmpau reclassified to 700m Twmpau

There has been a reclassification to the listing of Twmpau (thirty welsh metre prominences and upward) hills due to analysis of LIDAR data by Aled Williams.  The hill was listed in the 800m height band of P30 Twmpau hills and it has now been reclassified to a 700m Twmpau.

The criteria for 700m Twmpau status is all Welsh hills at or above 700m and below 800m in height with 30m minimum drop, whilst the criteria for 800m Twmpau status is all Welsh hills at or above 800m and below 900m in height with 30m minimum drop.  Details to the 700m Twmpau were published on Mapping Mountains on 15^th April 2015, and details to the 800m Twmpau were published on Mapping Mountains on the 15^th March 2015.

The name of the hill is Pen y Gadair Fawr and it had been listed in the 800m height band of Twmpau hills, based on the 800m summit spot height that appears on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  With the 800m height on Ordnance Survey maps originating from the 2624ft (799.8m) imperial bench mark height on the series of old Six-Inch maps.

The hill is situated on one of the central ridges that forms the Mynyddoedd Duon (Black Mountains) group of hills with its Cardinal Hill being Waun Fach (SO 215 299) and is placed in the Region of South Wales (Region C, Sub-Region C3).  It is situated between the steam valleys of the Grwyne Fawr to its north-east and the Grwyne Fechan to its south, with the town of Talgarth towards the north-west and Y Gelli Gandryll (Hay-on-Wye) towards the north.

As the hill is a part of designated open access land it can be accessed from most directions, however an extended circular walk taking in the ridge upon which it is positioned in conjunction with the ridge to its west is a good way to accustom oneself with this hill range.

The reclassification of Pen y Gadair Fawr to 700m Twmpau status is due to the analysis of LIDAR data by Aled Williams.  LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales.

Aled’s analysis of LIDAR data gives the hill the following details:

Pen y Gadair Fawr

Summit Height:  799.8m

Summit Grid Reference:  SO 22944 28758

Bwlch Height:  753.2m

Bwlch Grid Reference:  SO 22657 29359

Drop:  46.6m

Therefore, the 799.8m LIDAR data produced for the summit position at SO 22944 28758 and the 753.2m LIDAR data produced for the bwlch position at SO 22657 29359 gives this hill 46.6m of drop, and as the summit height is below 800m it is reclassified to a 700m Twmpau with a 799.8m summit height.

This now revises the total in the 800m and 700m Twmpau which will be updated accordingly.

The full details for the hill are:

Cardinal Hill:  Waun Fach

Summit Height:  799.8m (LIDAR data)

Name:  Pen y Gadair Fawr

OS 1:50,000 map:  161

Summit Grid Reference:  SO 22944 28758  

 

Drop:  46.6m (LIDAR data)

Pen y Gadair Fawr (SO 229 287) now reclassified from an 800m Twmpau to a 700m Twmpau

My thanks to Aled Williams for sending the details of this hill to me

Myrddyn Phillips (October 2017)