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

Bryn Llwyd (SN 772 763) – 400m Sub-Pedwar addition

There has been an addition to the listing of the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data.

This was initiated by Joe Nuttall who produced a summit analysis programme that used LIDAR with an alternative height map (DEM) allowing identification of summits and bylchau and thereby drops.  The resulting spreadsheet that Joe produced contains over 29,600 hills.

This spreadsheet is being evaluated by a number of people, including Ronnie Bowron, who passed the details of this hill to us.

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 Y Pedwarau list are five categories of sub hills, with this hill being added to the 400m Sub-Pedwar category.  The criteria for 400m Sub-Pedwar status 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 Bryn Llwyd, and it is adjoined to the Elenydd group of hills, which are situated in the northern part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the A44 road to its north-east, the A4120 to its north-west and the B4574 road to its south, and has the village of Pontarfynach (Devil’s Bridge) towards the west.

When the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013, this hill was not included as it was listed with an estimated c 19m of drop, based on the 474m summit spot height and an estimated c 455m bwlch height, with the latter based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map.

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

With the summit analysis programme produced by Joe Nuttall and the examination of its data by Ronnie Bowron, the details for this hill have now been re-assessed against mapping on the OS Maps website.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and used to appear on the online Vector Map Local.  This re-assessment resulted in the hill being listed with an estimated c 453m bwlch height based on interpolation of 5m contouring between 450m – 455m, resulting in the drop value increasing to an estimated c 21m. 

Extract from the OS Maps website

Therefore, the addition of this hill to 400m Sub-Pedwar status is due to re-assessment of detail derived from contemporary maps produced from Ordnance Survey data, resulting in a 474m summit height and an estimated c 453m bwlch height, with these values giving this hill c 21m of drop which is sufficient for it to be classified as a 400m Sub-Pedwar.

The full details for the hill are:

Group:  Elenydd 

Name:  Bryn Llwyd

OS 1:50,000 map:  135, 147

Summit Height:  474m (spot height)

Summit Grid Reference:  SN 77211 76332 (spot height)

Bwlch Height:  c 453m (interpolation)

Bwlch Grid Reference:  SN 77520 76421 (interpolation)

Drop:  c 21m (spot height summit and interpolated 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 (September 2020)