Monday, 26 December 2016

Mapping Mountains – Hill Reclassifications – Y Pedwarau

Pt. 408.0m, Hirfynydd (SN 822 051) - 400m Sub-Pedwar deletion

There has been a deletion of a 400m Sub-Pedwar by analysis of LIDAR data by Aled Williams.  The 400m Sub-Pedwarau are the Welsh hills at or above 400m and below 500m in height with a drop between 20m and below 30m.

The hill is connected to the Fforest Fawr group of hills with its Cardinal Hill being Hirfynydd (SN 839 076) and is placed in the Region of South Wales (C-2).  The hill is positioned above the villages of Y Creunant (Crynant) in Cwm Dulais (Dulais Valley) to its west and Resolfen (Resolven) in Cwm Nedd (Vale of Neath) to its south, and is best ascended via Sarn Helen; the ancient Roman Road that follows the ridge crest toward the higher connecting hill of Hirfynydd.  

As the authors do not know an individual name for the hill we are following the extended point (Pt. 408.0m) notation principal and listing it as Pt. 408.0m, Hirfynydd, and prior to the analysis of LIDAR data the hill was listed with c 20m of drop based on a 408m summit spot height on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height from contour interpolation of c 388m.

As Aled was analysing other hills in the vicinity against LIDAR data, he did likewise with Pt. 408.0m, Hirfynydd.  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:

Pt. 408.0m, Hirfynydd

Summit Height:  408.0m

Summit Grid Reference:  SN 82213 05117

Bwlch Height:  389.5m

Bwlch Grid Reference:  SN 82356 05671

Drop:  18.5m

Therefore, the 408.0m LIDAR data produced for the summit position at SN 82213 05117 and the 389.5m LIDAR data produced for the bwlch position at SN 82356 05671 is insufficient for this hill to retain its 400m Sub-Pedwar status with only 18.5m of drop, and therefore Pt. 408m, Hirfynydd is deleted from 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:  Hirfynydd

Summit Height:  408.0m (LIDAR data)

Name:  Pt. 408m, Hirfynydd

OS 1:50,000 map:  160

Summit Grid Reference:  SN 82213 05117

Drop:  18.5m (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:




Pt. 408.0m, Hirfynydd (LIDAR data) (SN 822 051) 18.5m drop

Myrddyn Phillips and Aled Williams (December 2016)

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