Mapping Mountains – Significant Height Revisions – 500m Twmpau and Welsh Highlands – Uchafion Cymru

 

Tryfan (SH 596 580) 

There has been a Significant Height Revision to a hill that is listed in the 500m Twmpau and the Welsh Highlands – Uchafion Cymru, 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. 

Tryfan (SH 596 580)

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

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with an accompanying sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or above 500m and below 600m in height that have 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 is published on Mapping Mountains in Google Doc format.

500m Twmpau by Myrddyn Phillips

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 Highlnads - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The name the hill is listed by is Tryfan 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 has the village of Llanberis towards the north-west.

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

A basic levelling survey conducted by Myrddyn Phillips on the 25.06.04 gave this hill 67ft (20.4m) of drop and therefore it was included in the listing that later became known as the Welsh Highlands – Uchafion Cymru.  However, this drop value was at odds with detail on the contemporary Ordnance Survey 1:25,000 Explorer map which has an uppermost 560m summit contour and bwlch contouring between 550m – 560m, with interpolation giving an estimated c 555m bwlch height. 

Extract from the interactive mapping hosted on the WalkLakes website

The drop value ascertained fron the basic levelling survey implied that current Ordnance Survey contouring on the 1:50,000 Landranger and 1:25,000 Explorer map is missing an uppermost 570m ring contour, and this is evidenced by the 577m summit spot height on the mapping hosted on the WalkLakes website.  This website hosts an interactive map originated from the Ordnance Survey Open Data programme and has many spot heights not on other publicly available maps. 

The Trimble GeoXH 6000 gathering data at the summit of Tryfan (SH 596 580)

The summit of this hill was subsequently surveyed with the Trimble GeoXH 6000 on the 09.09.14, resulting in a 577.2m summit height positioned at SH 59636 58098, and this height 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.

Therefore, the new listed summit height of this hill is 577.2m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SH 59636 58098 and is 17.2m higher than the uppermost 560m contour that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Yr Wyddfa

Name:  Tryfan

OS 1:50,000 map:  115

Summit Height (New Height):  577.2m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 59636 58098 (Trimble GeoXH 6000)  

Bwlch Height:  556.4m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SH 59683 57996 (Trimble GeoXH 6000)

Drop:  20.8m (Trimble GeoXH 6000)

 

Myrddyn Phillips and Aled Williams (August 2024)