Mapping Mountains – Significant Height Revisions – Y Pedwarau – The 400m Hills of Wales

Moel Wnog (SH 735 440) 

There has been a Significant Height Revision 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 detail produced by Joe Nuttall in his surface analysis progamme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Aled Williams and Myrddyn Phillips. 

LIDAR image of Moel Wnog (SH 735 440)

The criteria for the list that this height revision 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 now being listed in 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 Moel Wnog and it is adjoined to the Arenig Fach group of hills, which are situated in the north-westerly part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor road to its west, the A470 road farther to its west, the B4391 road to its south-west and the B4407 road to its south-east, and has the village of Ffestiniog towards the south-west.

When the original 400m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 29 of drop, based on an estimated c 468m summit height and an estimated c 439m bwlch height, with both heights 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

Prior to the 1^st edition of the Y Pedwarau being published by Europeaklist in May 2013, the details for this hill were re-evaluated and it was listed as a Pedwar with an estimated c 34m of drop, based on the 473m summit spot height that appears on the Harvey 1:40,000 British Mountain Map and an estimated c 439m bwlch height.

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 Moel Wnog (SH 735 440)

LIDAR analysis gives the highest ground on this hill as 471.3m positioned at SH 73522 44084, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 471.3m and this was derived from LIDAR analysis, this is 3.3m higher than the originally listed estimated height of c 468m which was based on interpolation of the uppermost 460m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Arenig Fach 

Name:  Moel Wnog 

OS 1:50,000 map:  124

Summit Height (New Height):  471.3m (LIDAR) 

Summit Grid Reference:  SH 73522 44084 (LIDAR) 

Bwlch Height:  441.5m (LIDAR) 

Bwlch Grid Reference:  SH 73597 44355 (LIDAR) 

Drop:  29.8m (LIDAR)

 

Myrddyn Phillips and Aled Williams (August 2023)