Mapping Mountains – Hill Reclassifications – Y Trichant

Cerrig y Ddinas (SH 754 739) – Sub-Trichant reclassified to Trichant

There has been a reclassification to a hill that is listed in the Y Trichant, with the summit height and its position initially ascertained from LIDAR analysis and the summit height, bwlch height and their locations, the drop and status of the hill subsequently confirmed by a survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter taking place on the 22^nd May 2019.

Cerrig y Ddinas (SH 754 739)

The criteria for the list that this reclassification applies to are:

Y Trichant – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017.

The name of the hill is Cerrig y Ddinas and it is adjoined to the Carneddau 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 A55 road and the coast to its north, and has the town of Conwy towards the north-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the Hills to be surveyed sub list as it did not meet the criteria then used for the main P30 list; however the main P30 and accompanying sub list has now been standardised and interpolated heights and drop values also included.

When this list was standardised and interpolated heights also included this hill was listed with an estimated c 26m of drop, based on the 312m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map which was prioritised in favour of the 314m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map, and an estimated bwlch height of c 286m based on interpolation of 10m contouring on the contemporary Ordnance Survey 1:25,000 Explorer map.

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

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

The details for this hill were re-examined when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals.  The mapping on OS Maps shows this hill with bwlch contouring between 280m – 285m with an estimated height of c 284m giving this hill a drop value nearer 30m.

Extract from the OS Maps website

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales, however LIDAR coverage only takes in the summit of this hill. 

LIDAR summit image of Cerrig y Ddinas

The reclassification of this hill to Trichant status is due to a Trimble GeoXH 6000 bwlch and summit survey, resulting in a 313.5m summit height and a 283.0m bwlch height, with these values giving this hill 30.5m of drop, which is sufficient for this hill to be classified as a Trichant.

 

The full details for the hill are:

Group:  Carneddau

Name:  Cerrig y Ddinas

OS 1:50,000 map:  115

Summit Height:  313.5m (converted to OSGM15)

Summit Grid Reference:  SH 75427 73948

Bwlch Height:  283.0m (converted to OSGM15)

Bwlch Grid Reference:  SH 75140 73786

 

Drop:  30.5m (converted to OSGM15)

For details on the survey of this hill

Myrddyn Phillips (August 2019)