Mapping Mountains – Hill Reclassifications – Y Pedwarau - The 400m Hills of Wales

Allt y Genlli (SN 985 950) – 390m Double Sub-Pedwar reclassified to 390m Sub-Pedwar

THIS HILL HAS SUBSEQUENTLY BEEN RE-INSTATED TO 390m DOUBLE SUB-PEDWAR STATUS

The following details have been superseded by a survey conducted by John Barnard, Chris Crocker and Graham Jackson using a Leica GS15 with the result that this hill has been re-instated to 390 Double Sub-Pedwar status with 28.7m of drop.

Below is the Hill Reclassifications post prior to the Leica GS15 survey:


There has been a reclassification 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 reclassified from a 390m Double Sub-Pedwar to a 390m Sub-Pedwar.  The 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, with the criteria for 390m Sub-Pedwar status being all Welsh hills at or above 390m and below 400m in height that have a minimum 30m of drop.

Prior to analysis of LIDAR data the hill was listed as a 390m Double Sub-Pedwar and its reclassification is dependent upon the LIDAR data analysis of it, and its southerly adjacent hill of Mynydd Garth Pwt, because of this the previously listed details of both hills based on map data are given below:

Allt y Genlli (previously listed as 390m Double Sub-Pedwar)

Summit Height:  394m (OS 1:25,000 Explorer map)

Summit Grid Reference:  SN 985 950

Bwlch Height:  367m (OS enlarged mapping hosted on the Geograph website)

Bwlch Grid Reference:  SN 983 944

Drop:  27m

Mynydd Garth Pwt (listed as 390m Sub-Pedwar)

Summit Height:  397m (OS 1:50,000 Landranger and 1:25,000 Explorer maps)

Summit Grid Reference:  SN 981 941

Bwlch Height:  c 325m

Bwlch Grid Reference:  SN 973 941

Drop:  c 72m

The hill is a part of the Pumlumon range with its Cardinal Hill being Bryn Amlwg (SN 921 973) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B2).  The hill is situated to the south of the A 470 and is positioned between the small communities of Carno to its west north-west and Clatter to its east. 

Although the whole upper part of the hill is a part of designated open access land it is also immersed in conifer plantation.  The summit of the hill is encircled by a forest track and for those determined souls who wish to visit; an approach from the north using this track may be the best option, however only an on-site visit could determine how problematic an ascent could be.

The name of the hill is Allt y Genlli and its reclassification from 390m Double Sub-Pedwar to 390m Sub-Pedwar status is dependent upon its adjacent southerly hill of Mynydd Garth Pwt and 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 these two hills the following details:

Allt y Genlli

Summit Height:  398.9m

Summit Grid Reference:  SN 98508 95042

Bwlch Height:  325.7m

Bwlch Grid Reference:  SN 97387 94159

Drop:  73.2m

Mynydd Garth Pwt

Summit Height:  397.8m

Summit Grid Reference:  SN 98154 94173

Bwlch Height:  367.3m

Bwlch Grid Reference:  SN 98385 94438

Drop:  30.5m

Therefore, as the 398.9m LIDAR data produced for the summit position of Allt y Genlli at SN 98508 95042 is higher than the 397.8m LIDAR data produced for the summit position of Mynydd Garth Pwt at SN 98154 94173, the lower bwlch is the critical bwlch for the higher of the two hills, therefore the listed bwlch position of each hill is swapped.

The full details for the two hills are:

Cardinal Hill:  Bryn Amlwg

Summit Height:  398.9m (LIDAR data)

Name:  Allt y Genlli

OS 1:50,000 map:  136

Summit Grid Reference:  SN 98508 95042

  

Drop:  73.2m (LIDAR data)

Cardinal Hill:  Bryn Amlwg

Summit Height:  397.8m (LIDAR data)

Name:  Mynydd Garth Pwt

OS 1:50,000 map:  136

Summit Grid Reference:  SN 98154 94173 

 

Drop:  30.5m (LIDAR data)

The total for Y Pedwarau remains at 443 hills with eight additions, and twelve reclassifications to 400m Sub-Pedwar status since publication of the list by Europeaklist in May 2013.

The total for the 390m Double Sub-Pedwarau decreases by one to 25 hills and the total for the 390m Sub-Pedwarau increases by one to 38 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:

Y Pedwarau

Y Pedwarau – 400m Sub-Pedwarau

Y Pedwarau – 390m Sub-Pedwarau

Y Pedwarau – 390m Double Sub-Pedwarau

Myrddyn Phillips and Aled Williams (May 2017)