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

Moel Tryfan (SH 517 559) - 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 initially derived from LIDAR analysis conducted by Aled Williams with a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

Moel Tryfan (SH 517 559)

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 included in 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 Moel Tryfan, and it is adjoined to the Moel Hebog group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with a minor road to its west and south, the A487 road farther to its west, the B4418 road farther to its south and the A4085 road to its east, and has the village of Nantlle towards the south.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips was published on Geoff Crowder’s v-g.me website, this hill was not included in the 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 this hill was still not included, as with no summit spot height and bwlch contouring depicted on the contemporary Ordnance Survey 1:50,000 and 1:25,000 Explorer map as not being continuous due to the ground hereabouts having been disturbed from quarrying activity, estimating a drop value was difficult.

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

However, it was not until LIDAR became available and the subsequent Trimble GeoXH 6000 survey 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 image of Moel Tryfan (SH 517 559)

Therefore, the addition of this hill to 400m Sub-Pedwar status is due to LIDAR analysis and a subsequent Trimble GeoXH 6000 survey, resulting in a 405.4m summit height and a 384.4m bwlch height, with these values giving this hill 21.0m of drop, which is sufficient for it to be classified as a 400m Sub-Pedwar.     

The full details for the hill are:

Group:  Moel Hebog

Name:  Moel Tryfan

OS 1:50,000 map:  115

Summit Height:  405.4m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 51780 55926 (Trimble GeoXH 6000)  

Bwlch Height:  384.4m (LIDAR) 

Bwlch Grid Reference:  SH 51509 55891 (LIDAR)

Drop:  21.0m (Trimble GeoXH 6000 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 (December 2016)