Friday, 21 July 2017

Mapping Mountains – Hill Reclassifications – Y Pedwarau


Disgwylfa (SN 982 663) – 400m Sub-Pedwar deletion

There has been a deletion to the listing of Y Pedwarau due to analysis of LIDAR data by Aled Williams.  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 deleted from the 400m Sub-Pedwar categoryThe criteria for 400m Sub-Pedwar qualification is all Welsh hills at or above 400m and below 500m in height with 20m or more and below 30m of drop.

Prior to analysis of LIDAR data the hill was listed with 20m of drop based on the 477m summit spot height and the 457m bwlch spot height that appear on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The hill is situated in the Hirddywel range with its Cardinal Hill being Gwastedyn Hill (SN 986 661) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B1), and is positioned above the A 470 road which is to its north-west and has the town of Rhaeadr Gwy (Rhayader) to the north north-west.

As the summit of the hill is not a part of designated open access land permission should be sought to visit, however common sense should prevail as the summit is a local landmark and as the name of the hill implies it is a look out position, and as open access land is close to the high point to its immediate south, a visit to its summit should not course any dispute.

The name of the hill is Disgwylfa, although the area of the summit is also named as a part of Gwastedyn Hill, and its deletion from 400m 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:


Disgwylfa

Summit Height:  475.5m

Summit Grid Reference:  SN 98210 66310

Bwlch Height:  456.1m

Bwlch Grid Reference:  SN 98422 66294

Drop:  19.4m


Therefore, the 475.5m LIDAR data produced for the summit position at SN 98210 66310 and the 456.1m LIDAR data produced for the bwlch position at SN 98422 66294 gives this hill 19.4m of drop which is insufficient for its continued inclusion as a 400m Sub-Pedwar.


The full details for the hill are:

Cardinal Hill:  Gwastedyn Hill

Summit Height:  475.5m (LIDAR data)

Name:  Disgwylfa

OS 1:50,000 map:  136, 147

Summit Grid Reference:  SN 98210 66310

Drop:  19.4m (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 overall total for the 400m Sub-Pedwarau is now 218 with 25 hills being added and 20 hills being taken out of this category since publication of the list by Europeaklist in May 2013.

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:










Disgwylfa (SN 982 663) is now deleted from the 400m Sub-Pedwar category

Myrddyn Phillips and Aled Williams (July 2017)



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