Friday, 3 February 2017

Mapping Mountains – Hill Reclassifications – Y Pedwarau

Banc y Llyn (SN 804 652) - 400m Sub-Pedwar addition

There is a new hill joining the ranks of 400m Sub-Pedwarau by analysis of LIDAR data by Aled Williams.  The 400m Sub-Pedwarau is one of five categories of sub hills that accompany the main Y Pedwarau list, with the criteria for 400m Sub-Pedwar status being all Welsh hills at or above 400m and below 500m in height with 20m or more and below 30m of drop.

The hill is situated in the Elenydd group of hills which is one of the wildest hill ranges in Wales, with its Cardinal Hill being Drygarn Fawr (SN 862 584) and is placed in the Region of Mid and West Wales (B-2).  The hill is positioned between the small communities of Pontrhydfendigaid towards the west and the Elan Village towards the east, and is situated above Llyn Gynon which is to its south-west.

Whatever way one approaches, it is relatively remote for a Welsh hill with access from the west probably being the easiest with a track leaving the paved road that heads east from the ruins of Strata Florida Abbey toward the old farm house of Garreglwyd, from here the going will be rough with the prospect of it also being wet as whatever way one approaches the hill at least one stream has to be negotiated, with the hill positioned with wetlands to its immediate north and streams feeding toward Llyn Gynon to its west and east and the lake toward the south.

The name of the hill is Banc y Llyn and prior to the analysis of LIDAR data and its subsequent listing as a 400m Sub-Pedwar it has been listed as a Pellennig hill (Y Pellennig – the Remotest Hills of Wales [Mapping Mountains Publications July 2016]) with c 19m of drop based on its 474m summit spot height on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 455m based on bwlch contouring between 450m – 460m.

As Aled was analysing other hills in the vicinity against LIDAR data, he did likewise with Banc y Llyn.  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:

Banc y Llyn

Summit Height:  473.3m

Summit Grid Reference:  SN 80496 65235

Bwlch Height:  452.0m

Bwlch Grid Reference:  SN 80404 65691

Drop:  21.7m

Therefore, the 473.7m LIDAR data produced for the summit position at SN 80496 65235 and the 452.0m LIDAR data produced for the bwlch position at SN 80404 65691 is sufficient for this hill to be classified as a 400m Sub-Pedwar with 21.7m of drop, and therefore Banc y Llyn is included in the listing of 400m Sub-Pedwar hills and the list of the Y Pedwarau will be updated accordingly.  The list of Pedwar hills is available from the Haroldstreet website (January 2014) with all subsequent changes available via the Mapping Mountains site.

The full details for the hill are: 

Cardinal Hill:  Drygarn Fawr  

Summit Height:  473.7m (LIDAR data)  5

Name:  Banc y Llyn  

OS 1:50,000 map:  135, 136, 147  

Summit Grid Reference:  SN 80496 65235  

Drop:  21.7m (LIDAR data)

The list of additions, reclassifications and deletions from the 400m Sub-Pedwar list since the 1st edition of the Y Pedwarau was published by Europeaklist are as follows:


Banc y Llyn (LIDAR data) (SN 804 652) 21.7m drop



Myrddyn Phillips and Aled Williams (February 2017)

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