Mapping Mountains – Hill Reclassifications – Y Pedwarau

Yr Allt (SO 074 755) – 400m Sub-Pedwar deletion

There has been a deletion from 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 category.  The 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 this hill was listed with 25m of drop based on the 436m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 411m bwlch spot height that appears on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The name of the hill is Yr Allt and it is situated in the Hirddywel range of hills with its Cardinal Hill being Pt. 508m (SO 041 783) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B1).  The hill is positioned above the stream valleys of the Crychell Brook to its west and the Afon Ieithon (River Ithon) to its east, with the small community of Llanbadarn Fynydd towards the north-east and Llananno towards the east south-east.

The summit of the hill is a part of designated open access land with the long distance footpath of Glyndŵr’s Way just to the east of the summit.  There are public footpaths that lead to the open access land from the north-west and south-east of the hill.

The deletion of Yr Allt 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:

Yr Allt

Summit Height:  437.6m

Summit Grid Reference:  SO 07419 75572

Bwlch Height:  418.5m

Bwlch Grid Reference:  SO 07410 75952

Drop:  19.1m

Therefore, the 437.6m LIDAR data produced for the summit position at SO 07419 75572 and the 418.5m LIDAR data produced for the bwlch position at SO 07410 75952 gives this hill 19.1m of drop which is insufficient for its retention as a 400m Sub-Pedwar.

The full details for the hill are:

Cardinal Hill:  Pt. 508m (SO 041 783)  

Summit Height:  437.6m (LIDAR data)

Name:  Yr Allt

OS 1:50,000 map:  136, 147

Summit Grid Reference:  SO 07419 75572

Drop:  19.1m (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 219 with 27 hills being added and 21 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:

Y Pedwarau

Y Pedwarau – 400m Sub-Pedwarau

Y Pedwarau – 390m Sub-Pedwarau

Y Pedwarau – 390m Double Sub-Pedwarau

Myrddyn Phillips and Aled Williams (September 2017)