Mapping Mountains – Summit Relocations – Y Pedwarau – The 400m Hills of Wales

 

Wenallt (SN 967 784) 

There has been a Summit Relocation to a hill that is listed in 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 LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips. 

LIDAR image of Wenallt (SN 967 784)

The criteria for the list that this summit relocation 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; 500m Sub-Pedwarau, 500m Double Sub-Pedwarau, 400m Sub-Pedwarau, 390m Sub-Pedwarau and the 390m Double Sub-Pedwarau.  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 Wenallt, 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 a minor road to its north-west and south, the A470 road to its west, and the B4518 road to its east, and has the town of Llanidloes towards the north.

When the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013, this hill was listed with 40m of drop, based on the 435m summit spot height positioned at SN 96856 78457 that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the 395m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

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

However, it was not until LIDAR became available that the details for this hill 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 summit image of Wenallt (SN 967 784)

LIDAR analysis gives the highest ground on this hill as 433.0m positioned at SN 96743 78468, as opposed to LIDAR giving 432.7m positioned at SN 96838 78430, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or the de-twinning of a summit, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Therefore, the height produced by LIDAR analysis to the summit of this hill is 433.0m and is positioned at SN 96743 78468.  This position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 113 metres westward from the position of the map spot height and approximately 95 metres from where LIDAR places the top of the high ground to the east of where the summit of this hill is now positioned.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Hirddywel 

Name:  Wenallt 

OS 1:50,000 map:  136, 147

Summit Height:  433.0m (LIDAR) 

Summit Grid Reference (New Position):  SN 96743 78468 (LIDAR) 

Bwlch Height:  394.0m (LIDAR) 

Bwlch Grid Reference:  SN 95366 78745 (LIDAR) 

Drop:  39.0m (LIDAR)

 

Myrddyn Phillips and Aled Williams (October 2025)