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

Drysgol (SN 946 744) - Pedwar reclassified to 400m Sub-Pedwar

There has been a reclassification to the listing of the Y Pedwarau – The 400m Hills of Wales, due to a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips, with the summit height and its location derived from a subsequent Leica GS15 survey conducted by John Barnard and Graham Jackson, and the bwlch height and its location, the drop and status of the hill subsequently derived from LIDAR analysis conducted by Myrddyn Phillips.

Drysgol (SN 946 744)

The criteria for the list that this addition applies to are:

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills, with this hill being reclassified to the 400m Sub-Pedwar category.  The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Drysgol and it is adjoined to the Hirddywel group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B2), and it is positioned with the A470 road to its south-west and the B4518 road to its east, and has the town of Llanidloes towards the north.

When the original 400m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list, as with a 484m summit spot height and a 457m spot height on the area of the bwlch that appear on the contemporary Ordnance Survey 1:25,000 Explorer map, it was considered to have 27m of drop.

Extract from the Ordnance Survey 1:25,000 Explorer map

The hill was subsequently reclassified to Pedwar status due to a basic levelling survey of the bwlch area conducted by Myrddyn Phillips, based on the lay of land in relation to the position of a fence junction where the 457m spot height appears on the Ordnance Survey 1:25,000 Explorer maps.  This survey gave the hill 102ft (31.1m) of drop, and although relying on the accuracy of spot heights which have a margin of +/- 3m, it was judged sufficient to include the hill as a Pedwar as interpolation of bwlch contouring also implied an estimated c 31m of drop, based on an estimated c 453m bwlch height.

The hill was reclassified to Pedwar status due to a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips, resulting in a 483.6m summit height and a 454.4m bwlch height, with these values giving this hill 29.2m of drop.

Gathering data with the Trimble GeoXH 6000 on the summit area of Drysgol

The hill was subsequently surveyed by John Barnard and Graham Jackson using a Leica GS15, resulting in a 483.7m summit height and a 454.2m bwlch height, with these values giving this hill 29.6m of drop.

However, it was not until LIDAR became available that the details for this hill compared to the previous surveys could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

LIDAR image of Drysgol (SN 946 744)

Therefore, the confirmation of the reclassification of this hill to 400m Sub-Pedwar status is due to a Leica GS15 summit survey and LIDAR bwlch analysis, resulting in a 483.7m summit height and a 454.3m bwlch height, with these values giving this hill 29.5m of drop, which is insufficient for Pedwar status.

The full details for the hill are:

Group:  Hirddywel

Name:  Drysgol

OS 1:50,000 map:  136, 147

Summit Height:  483.7m (converted to OSGM15, Leica GS15)

Summit Grid Reference:  SN 94626 74408 (Leica GS15)

Bwlch Height:  454.3m (LIDAR)

Bwlch Grid Reference:  SN 93907 75683 (LIDAR)   

Drop:  29.5m (Leica GS15 summit and LIDAR bwlch) 

For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales 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 (March 2016)