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

Craig y Garreg Lwyd (SH 730 427)  

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 a Leica GS15 survey conducted by John Barnard and Graham Jackson.

Craig y Garreg Lwyd (SH 730 427)

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 list are five categories of sub hills, with this hill being re-instated from 400m Sub-Pedwar status.  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 Craig y Garreg Lwyd, 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 a minor road to its north-west, the B4391 road to its south and the B4407 road to its east, and has the village of Ffestiniog towards the west south-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 included in the main P30 list with a non-interpolated c 470 summit height, with its inclusion based on a basic levelling survey conducted by Myrddyn Phillips, resulting in 99ft/30.2m of drop.

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

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 35m of drop, based on the 478m summit spot height and the 443m 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, and these are the details given the hill when the 1^st edition of the Y Pedwarau, now co-authored by Myrddyn Phillips and Aled Williams was published by Europeaklist in May 2013.

However, it was not until the Leica GS15 survey that its listed summit height was ascertained.  This survey gives the highest ground on this hill as 473.8m positioned at SH 73043 42743, 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, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or other GNSS equipment or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 473.8m and this was derived from a Leica GS15 survey, this is 4.2m lower than the previously listed summit height, which was based on the 478m spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

The full details for the hill are:

Group:  Arenig Fach

Name:  Craig y Garreg Lwyd

OS 1:50,000 map:  124

Summit Height (New Height):  473.8m (converted to OSGM15)

Summit Grid Reference:  SH 73043 42743

Bwlch Height:  443.6m (converted to OSGM15)

Bwlch Grid Reference:  SH 73220 42799   

Drop:  30.2m

Myrddyn Phillips and Aled Williams (March 2016)