Mapping Mountains – Significant Height Revisions – 600m Twmpau and Yr Uchafion

Cnicht (SH 645 466)

There has been a Significant Height Revision to a hill that is listed in the 600m Twmpau and Yr Uchafion, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips on the 23^rd March 2019.

Cnicht (SH 645 466)

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

600m Twmpau – Welsh hills at or above 600m and below 700m in height that have 30m minimum drop, with an accompanying sub category entitled the 600m Sub-Twmpau consisting of all Welsh hills at or above 600m and below 700m 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.

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to this list appearing on Mapping Mountains on the 4^th November 2015.

The name of the hill is Cnicht, and it is adjoined to the Moelwynion range of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A4085 road to its south-west, the A498 road to its north-west and the A470 road towards the east, and has the small community of Croesor towards the south-west and the town of Blaenau Ffestiniog towards the east.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with a 689m summit height that appears as a spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

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

The summit height produced by the Trimble GeoXH 6000 survey is 690.7m, 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 any other GNSS receiver, 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.

The Trimble GeoXH 6000 gathering data at the summit of Cnicht

Therefore, this hill’s new summit height is 690.7m and this was produced by surveying with the Trimble GeoXH 6000, this is 1.7m higher than its previously listed height of 689m which appears as a spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, however this new height is in accordance with the 5m contouring on OS Maps. 

 

Extract from the OS Maps website

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Moelwynion

Name:  Cnicht

OS 1:50,000 map:  115

Summit Height (New height):  690.7m (converted to OSGM15)

Summit Grid Reference:  SH 64545 46613 

 

Bwlch Height:  585.7m (converted to OSGM15)

Bwlch Grid Reference:  SH 65589 47707

Drop:  105.0m

For details on the survey of this hill

Myrddyn Phillips and Aled Williams (July 2019)