Sunday, 2 July 2017

Mapping Mountains – Hill Reclassifications – Y Pedwarau



Cyrnau Mawr (SN 751 750) – 390m Double Sub-Pedwar addition

There has been an addition to the listing of Y Pedwarau due to analysis of LIDAR data by Aled Williams and subsequently confirmed via a survey with the Trimble GeoXH 6000.  Y Pedwarau is the title for the list of 400m hills of Wales and takes in all Welsh hills at or above 400m and below 500m in height that have a minimum 30m of drop, the list is a joint compilation between Myrddyn Phillips and Aled Williams and it commenced publication on Mapping Mountains on the 30.01.17.

Accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being included in the 390m Double Sub-Pedwar categoryThe criteria for 390m Double Sub-Pedwar status being  all Welsh hills at or above 390m and below 400m in height with 20m or more and below 30m of drop.

Prior to analysis of LIDAR data the hill was not classified but it was catalogued with c 16m of drop based on an estimated c 390m summit height and an estimated c 374m bwlch height, the latter height based on bwlch contouring between 370m – 380m.

The hill is a part of the Elenydd range with its Cardinal Hill being Pen y Garn (SN 798 771) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B2).  The hill is situated with the B 4574 to its north and the B 4343 to its west and is positioned between the small communities of Pontarfynach (Devil’s Bridge) to its north-west and Cwmystwyth to its east south-east.  

For those wishing to visit the summit the whole upper section of the hill is a part of designated open access land, and this has immediate access from the B 4343 to the west or from a public footpath from the same road that intersects with the open access lane.

The name of the hill is Cyrnau Mawr and its addition to 390m Double Sub-Pedwar 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:


Cyrnau Mawr

Summit Height:  391.4m

Summit Grid Reference:  SN 75155 75007

Bwlch Height:  369.8m

Bwlch Grid Reference:  SN 75343 74906

Drop:  21.6m


Therefore, the 391.4m LIDAR data produced for the summit position at SN 75155 75007 and the 369.8m LIDAR data produced for the bwlch position at SN 75343 74906 gives this hill 21.6m of drop which is sufficient for its inclusion as a 390m Double Sub-Pedwar, with the details from the Trimble GeoXH survey being 391.4m (converted to OSGM15) summit at SN 75154 75006 and 369.8m (converted to OSGM15) bwlch at SN 75342 24906, giving this hill 21.6m of drop. 


The full details for the hill are:

Cardinal Hill:  Pen y Garn

Summit Height:  391.4m (converted to OSGM15 Trimble, and LIDAR data)

Name:  Cyrnau Mawr

OS 1:50,000 map:  135, 147

Summit Grid Reference:  SN 75154 75006  

Drop:  21.6m (converted to OSGM15 Trimble, and LIDAR data)


The total for Y Pedwarau remains at 442 hills with nine additions, and fourteen reclassifications to 400m Sub-Pedwar status since publication of the list by Europeaklist in May 2013.

The total for the 390m Sub-Pedwarau remains at 38 hills, whilst the total for the 390m Double Sub-Pedwarau increases by one to 26 hills.

The list of Pedwar hills is available from the Haroldstreet website (January 2014) with all subsequent changes detailed on the Mapping Mountains site, with the list also having commenced publication on Mapping Mountains on the 30.01.17.

For the additions, reclassifications and deletions to Y Pedwarau reported on Mapping Mountains since the May 2013 publication of the list by Europeaklist please consult the following Change Registers:









Cyrnau Mawr (SN 751 750) confirmed as a 390m Double Sub-Pedwar



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