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

Bryn Glas (SH 735 420) - 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, with subsequent confirmation of its status from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

Bryn Glas (SH 735 420) confirmed as a 400m Sub-Pedwar

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 Bryn Glas, and it is adjoined to the Arenig Fach group of hills, which are situated in the central part of North Wales (Region C1, Sub-Region C1A), and it is positioned with the B4391 road to its south and the B4407 road to its east, and has the village of Ffestiniog towards the west.

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.

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

Due to a typo the classification of this hill as a 400m Sub-Pedwar was missed when assessing the information for the Europeaklist booklet published in May 2013, with the hill automatically qualifying for this sub list with a 416m summit spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and an estimated c 395m bwlch height, with these values giving this hill an estimated c 21m of drop.

The Trimble GeoXH 6000 gathering data at the summit of Bryn Glas

However, it was not until the subsequent Trimble GeoXH 6000 survey that the details for this hill could be accurately re-assessed.

The Trimble GeoXH 6000 gathering data at the bwlch of Bryn Glas

Therefore, the confirmation of the addition of this hill to 400m Sub-Pedwar status is due to a Trimble GeoXH 6000 survey, resulting in a 415.6m summit height and a 393.9m bwlch height, with these values giving this hill 21.7m of drop, which is sufficient for it to be classified as a 400m Sub-Pedwar.   

The full details for the hill are:

Group:  Arenig Fach

Name:  Bryn Glas

OS 1:50,000 map:  124

Summit Height:  415.6m (converted to OSGM15)

Summit Grid Reference:  SH 73505 42086

Bwlch Height:  393.9m (converted to OSGM15)

Bwlch Grid Reference:  SH 73647 42052 

Drop:  21.7m

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 (April 2014)