Mapping Mountains – Summit Relocations – Y Trechol – The Dominant Hills of Wales

Cae Alen (SH 781 758)

There has been a Summit Relocation to a hill that is listed in the Y Trechol – The Dominant Hills of Wales, with the summit height, its location, the drop and status 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 10^th October 2018.

LIDAR image of Cae Alen, Bwlch Mawr and Bryn Eithin

The criteria for the list that this summit relocation applies to are:

               

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name of the bounded land where the summit of this hill is situated is Cae Alen and this was derived from the Tithe map, and it is this name that the hill is now listed by.  The hill 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 B5106 road to its west and the Afon Conwy (River Conwy) to its east, and has the town of Conwy towards its north.

This summit relocation relates to three points, two of which are adjoined with the most northerly given a 130m summit spot height positioned at SH 781 758 on contemporary Ordnance Survey maps, this is adjoined to the central point which is given a small uppermost 130m ring contour positioned at SH 777 755, whilst the most southerly point is a separate P30 and also given a small uppermost 130m ring contour positioned at SH 775 752.

When the origin 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, two of these points were listed as separate P30s; with the northerly 130m map heighted summit positioned at SH 781 758 being prioritised over that of the central point positioned at SH 777 755.

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

The details for these hills were re-assessed when the Ordnance Survey Vector Map Local became available online, this map is hosted on the Geograph website and is entitled the Interactive Coverage Map, and as an uppermost contour ring should be prioritised over that of a same map heighted spot height the central point positioned at SH 777 755 was now prioritised for P30 status over the northerly 130m spot heighted point positioned at SH 781 758.  However, it was the southerly summit positioned at SH 775 752 that was now prioritised over the central summit positioned at SH 777 755 for Dominant status.

It was not until LIDAR became available and analysed that the details for these hills 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. 

LIDAR image of Bryn Eithin

The height produced by LIDAR analysis and a subsequent survey with the Trimble GeoXH 6000 confirmed the northerly summit as higher:

Northerly summit; Cae Alen:  129.1m at SH 78116 75814

Central summit; Bwlch Mawr:  128.4m at SH 77790 75561

Southerly summit; Bryn Eithin:  128.5m at SH 77584 75224

This comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.  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 relocations.

The Trimble GeoXH 6000 gathering data at the summit of Cae Alen

The Trimble GeoXH 6000 gathering data at the summit of Bryn Eithin

Therefore the height produced by the Trimble GeoXH 6000 survey is 129.1m positioned at SH 78116 75814, this position is given a 130m spot height on contemporary Ordnance Survey maps and is approximately 800m north-east from where the previously listed Dominant summit is situated which was surveyed as being 128.5m in height and positioned at SH 77584 75224.

The full details for the hill are:

Group:  Carneddau

Name:  Cae Alen

OS 1:50,000 map:  115

Summit Height:  129.1m (converted to OSGM15)

Summit Grid Reference (new position):  SH 78116 75814

Bwlch Height:  34.8m (LIDAR)

Bwlch Grid Reference:  SH 77629 74003 (LIDAR)

Drop:  94.3m (Trimble summit and LIDAR bwlch)

Dominance:  73.05% (Trimble summit and LIDAR bwlch)

For details of the summit survey of this hill

Myrddyn Phillips (April 2019)