Saturday, 23 January 2016

Mapping Mountains – Significant Height Revisions – 100m Twmpau and Y Trechol - The Dominant Hills of Wales


Bryn Maelgwyn (SH 795 805)

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau (thirty welsh metre prominences and upward) as well as Y Trechol - The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted on 16th January 2016.

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

100m Twmpau - These are the Welsh hills at or above 100m and below 200m in height that have a minimum drop of 30m. 

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The name of the hill is Bryn Maelgwyn and it is situated in the north-western part of the Rhos range of hills that is adjoined to Gogarth (Great Orme), and is positioned above the town of Llandudno.

The hill was surveyed in the company of Alex Cameron during a grey and damp day when we visited five P30 Twmpau hills over four separate small walks, with each summit being Trimbled.

Bryn Maelgwyn can be accessed from its south where a public footpath enters the Coed y Gell woodland.  However, to reach the summit one has to leave this footpath and the going thereafter becomes rougher with brambles and bracken creating a tangled web of undergrowth.  When I visited with Alex the underfoot conditions were never difficult and as the deciduous trees are growing relatively far apart from one another there are sufficient gaps in between to make good progress toward the summit.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with c 43m of drop and 40.57% Dominance based on an estimated summit height of of c 106m based on a 105m uppermost contour and 5m contour intervals which appear on the Ordnance Survey enlarged mapping hosted on the Geograph website, and an estimated bwlch height of c 63m, with the summit height produced by the survey with the Trimble being 102.1m (converted to OSGM15).  

Therefore this hill’s new summit height is 102.1m (converted to OSGM15) which is 3.9m lower than its previously estimated height of c 106m and 2.9m lower than its uppermost ring contour on the Ordnance Survey enlarged mapping hosted on the Geograph website.


The full details for the hill are:

Cardinal Hill:  Gogarth 

Summit Height (New Height):  102.1m (converted to OSGM15)

Name:  Bryn Maelgwyn

OS 1:50,000 map:  115

Summit Grid Reference:  SH 79580 80540 
         
Drop:  c 39

Dominance:  38.20%


Gathering data from the summit of Bryn Maelgwyn which resulted in this hill's significant height revision


Myrddyn Phillips (January 2016)