Saturday, 3 October 2015

Mapping Mountains – Significant Height Revisions – 200m Twmpau

Winllan Hill (SJ 217 214)  

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau 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 over two days; 28th / 29th August 2015.

The listing that this height revision affects is:

200m Twmpau - These are the Welsh hills at or above 200m and below 300m in height that have a minimum drop of 30m.  The word Twmpau is an acronym for thirty welsh metre prominences and upward.

The name of the hill is Winllan Hill and it is situated in the lower easterly hills of Y Berwyn, and is positioned above Llansanffraid-ym-Mechain which is situated beside where the Afon Cain flows in to the Afon Efyrnwy (River Vyrnwy).  The hill was initially surveyed in the late evening in the company of Mark Trengove after nourishing our appetite in the Bradford Arms in Llanymynech.

Access to Winllan Hill is good as public footpaths from the south, west, north and east head towards its summit and parking is easily found when approaching the hill from the west and north, this is also likely to be the case if approaching the hill from the east and south.  The high point of the hill is beside a fence and under a large overhanging tree, and is only a few metres from where a public footpath crosses the field that the summit is situated in.

Prior to the survey with the Trimble GeoXH 6000 the hill was listed as 216m high based on the spot height on the area of the summit that appears on the Ordnance Survey 1:25,000 Explorer map, and an estimated drop value of c 48m, based on bwlch contour interpolation which gives the height of the bwlch as c 168m.  However, there is significantly higher land to the north of where the 216m spot height is positioned on the ground.  With the height resulting from the survey of the summit with the Trimble GeoXH 6000 being 220.3m (converted to OSGM15).  

Therefore this hill’s new summit height is 220.3m (converted to OSGM15) which is 4.3m higher than the previously listed height of 216m which was based on the Ordnance Survey 1:25,000 Explorer map spot height.

The full details for the hill are:

Cardinal Hill:  Rhialgwm

Summit Height (New Height):  220.3m (converted to OSGM15)

Name:  Winllan Hill

OS 1:50,000 map:  126

Summit Grid Reference:  SJ 21709 21460 
Drop:  c 52m

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

Myrddyn Phillips (October 2015)

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