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

Bryn Dilyw (SN 835 779) – 400m Sub-Pedwar deletion

There has been a deletion 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 Ordnance Survey maps and aerial maps.

The criteria for the list that this deletion 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 deleted from 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.

The name the hill is listed by is Bryn Dilyw, 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 and the A470 road to its east, and has the village of Llangurig towards the east north-east.

When the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013, this hill was listed as a 400m Sub-Pedwar with an estimated c 21m of drop, based on a 480m summit height that appears as a spot height on the Ordnance Survey 1:50,000 Landranger map and a small uppermost contour that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 459m bwlch height based on interpolation of 10m contouring between 450m – 460m on the Ordnance Survey 1:25,000 Explorer map.

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

The details for this hill were re-assessed when the OS Maps website became available online.  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 461m bwlch height based on interpolation of 5m contouring between 460m – 465m.

Extract from the OS Maps website

This hill is immersed in a conifer plantation which also hosts wind turbines, and examination of aerial maps has concluded that the land where the small 480m ring contour appears is likely to be man-made as it resembles a deposit of earth from the construction of a turning point near to one of the turbines, therefore the summit height and position now used for this hill is given to the 478m spot height that appears on Ordnance Survey 1:25,000 Explorer maps.  When coupled with this hill’s estimated c 461m bwlch height, these values give this hill c 17m of drop.

Therefore, the deletion of this hill from 400m Sub-Pedwar status is due to re-assessment of detail on contemporary Ordnance Survey maps and the use of aerial maps, resulting in a 478m summit height and an estimated c 461m bwlch height, with these values giving this hill c 17m of drop which is insufficient for it to be classified as a 400m Sub-Pedwar.

The full details for the hill are:

Group:  Elenydd 

Name:  Bryn Dilyw

OS 1:50,000 map:  135, 136, 147

Summit Height:  478m (spot height)

Summit Grid Reference:  SN 83554 77970 (spot height)

Bwlch Height:  c 461 (interpolation)

Bwlch Grid Reference:  SN 83227 78076 (interpolation)

Drop:  c 17m (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 (March 2020)