Friday, 13 January 2017

Mapping Mountains – Hill Reclassifications – 500m Twmpau

Cwar yr Ystrad (SO 083 142) - 500m Sub-Twmpau addition

There has been a new addition to the listing of Twmpau (thirty welsh metre prominences and upward) hills due to analysis of LIDAR data by Aled Williams.  The hill is listed in the 500m height band of Sub-Twmpau, with the criteria for the sub hills being 500m or more and below 600m in height with 20m or more and below 30m of drop.  Details to this height band of the Twmpau were published on the Mapping Mountains site on 15th June 2015.

The hill did not appear in the Sub-List which accompanied the original Welsh P30 listings on Geoff Crowder’s website as the Sub-List only included hills whose map details showed that when surveyed they may stand a chance of qualification to the main P30 list, with the title of the Sub-List being ‘Hills to be surveyed.’  And as this hill is a part of a quarry current 1:50,000 and 1:25,000 Ordnance Survey maps do not give it any ring contours, as is the norm for areas of land that have been quarried.  The hill is of interest as it is only now listed as a Sub-Twmpau through the quarrying activities of past years that has resulted in producing a new bwlch for the hill.   Since first publication this Sub-List has been standardised and now includes all hills that have a minimum of 20m of drop and below 30m of drop.

The hill is situated in the southern part of the Bannau Brycheiniog (Brecon Beacons) group of hills with its Cardinal Hill being Pen y Fan (SO 012 215) and is placed in the Region of South Wales (C-2).  As its name suggests the hill is a part of a quarry with its qualification as a Sub-Twmpau partly due to past quarry activities, it is situated between the Pentwyn and Pontsticill Reservoirs to its west and the Talybont Reservoir to its north north-east, with the town of Merthyr Tudful to its south south-west and the small community of Trefil to its east south-east.

The hill can be accessed from a number of directions on public footpaths including from its south-west and from its north, whilst the route from the paved road north of Trefil also gives access onto the quarry track, but if wishing to ascend from this direction it should be noted that there is a barrier across the road beyond Trefil that is locked at 5.00pm and unlocked at 6.30am with online write ups stating this barrier is locked at weekends.

The name of the hill is Cwar yr Ystrad and its inclusion as a Sub-Twmpau is due to the analysis of LIDAR data by Aled.  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:

Cwar yr Ystrad

Summit Height:  579.9m

Summit Grid Reference:  SO 08358 14245

Bwlch Height:  558.9m

Bwlch Grid Reference:  SO 08376 14189

Drop:  21.0m

Therefore, the 579.9m LIDAR data produced for the summit position at SO 08358 14245 and the 558.9m LIDAR data produced for the bwlch position at SO 08376 14189 is sufficient for this hill to be classified as a Sub-Twmpau with 21.0m of drop.

This now revises the total in the 500m Twmpau which will be updated accordingly.

The full details for the hill are:

Cardinal Hill:  Pen y Fan

Summit Height:  579.9m (LIDAR data)

Name:  Cwar yr Ystrad

OS 1:50,000 map:  160

Summit Grid Reference:  SO 08358 14245  
Drop:  21.0m (LIDAR data)

A wintry scene with the new 500m Sub-Twmpau Cwar yr Ystrad in the background with its summit directly above the roof of Ed's car

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

Myrddyn Phillips (January 2017)

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