Mapping Mountains – Significant Height Revisions – 200m Twmpau

Coed Eryr (SH 636 508)

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, its location and the drop of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter taking place on the 6^th October 2018.

LIDAR image of Coed Eryr

The criteria for the list that this significant height revision applies to are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The name of the hill is Coed Eryr, and it is adjoined to the Moelwynion range of hills, which are situated in the western part of North Wales (Region A, Sub-Region A1), and it is positioned between the lakes of Llyn Dinas to ts south-west and Llyn Gwynant to its north-east, with the A498 road to its north-west, and has the village of Beddgelert towards the south-west.

When the original Welsh 200m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 241m summit height based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger map.

Extract from the Ordnance Survey 1:50,000 Landranger map

LIDAR summit image of Coed Eryr

The summit height produced by the Trimble GeoXH 6000 survey is 243.7m (converted to OSGM15), this is not a substantial height revision when compared to some revised heights, but it does come 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.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new listed summit height is 243.7m (converted to OSGM15) and this was produced by surveying with the Trimble GeoXH 6000, this is 2.7m higher than its previously listed height of 241m which appears as a spot height on the Ordnance Survey 1:50,000 Landranger map.

 

The Trimble GeoXH 6000 gathering data at the summit of Coed Eryr

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Moelwynion

Name:  Coed Eryr

OS 1:50,000 map:  115

Summit Height (New height):  243.7m (converted to OSGM15)

Summit Grid Reference:  SH 63612 50890

  

Bwlch Height:  181.6m (LIDAR)

Bwlch Grid Reference:  SH 64230 51021 (LIDAR)

Drop:  62.1m (Trimble summit and LIDAR bwlch)

For details on the summit survey of this hill

Myrddyn Phillips (March 2019)