Mapping Mountains – Significant Height Revisions – Welsh Highlands - Uchafion Cymru and 700m Twmpau

Llechog (SH 606 567)

There has been a Significant Height Revision to a hill that is listed in the Welsh Highlands – Uchafion Cymru and 700m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

Llechog (SH 606 567)

The criteria for the two listings that this height revision applies to are: 

Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop.  This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

700m Twmpau - Welsh hills at or above 700m and below 800m in height that have 30m minimum drop, with an accompanying sub list entitled the 700m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 700m and below 800m 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 list is authored by Myrddyn Phillips and the details to it were published on Mapping Mountains on the 15^th April 2015.

700m Twmpau by Myrddyn Phillips

The name the hill is listed by is Llechog and it is adjoined to the Yr Wyddfa group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A4086 road to its north-east and the A4085 road to its south-west, and has the village of Llanberis towards the north-west.

When the listing that later became known as the Welsh Highlands - Uchafion Cymru was first compiled this hill was listed with an estimated c 26m of drop, based on the 718m summit spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 692m bwlch height, based on interpolation of 10m contouring between 690m - 700m. 

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

However, it was not until the Trimble GeoXH 6000 survey that the details for this hill could be accurately re-assessed.  The summit height produced by this survey is 720.0m and is positioned at SH 60613 56751, 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.

The Trimble GeoXH 6000 gathering data from the summit of Llechog 

Therefore, the new listed summit height of this hill is 720.0mm and this was derived from a Trimble GeoXH 6000 survey, this is 2.0m higher than the previously listed summit height of 718m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group:  Yr Wyddfa

Name:  Llechog

OS 1:50,000 map:  115

Summit Height (New Height):  720.0m (converted to OSGM15)

Summit Grid Reference:  SH 60613 56751

  

Bwlch Height:  692.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 60557 56634

Drop:  28.0m

Myrddyn Phillips and Aled Williams (August 2015)