Thursday, 10 March 2016

Mapping Mountains – Trimble Surveys – Mynydd Hiraethog


23.02.16  Gallt y Celyn (SH 811 542, only bwlch surveyed [SH 815 544])   

The area of the bwlch of Gallt y Celyn

Just to the north of the busy A 5 as it nears its westward journey toward Betws-y-coed is a tranquil area of small hills, seemingly wildly situated where bracken and small rock outcrops predominate.  Amongst this land are situated occasional farms, with a narrow and steep minor road giving access to an otherwise undisturbed place where hill walkers are a rarity.  I’d visited this area in December 2013 when on my way to Nantlle to spend Christmas.  It was then the 24th and a chill wind blew hail showers across the land.  On that day I’d surveyed three tops, two of which are given a 258m spot height on Ordnance Survey maps.  The Trimble separated these tops giving one a height of 257.6m (SH 81121 54259) and the other a height of 257.1m (SH 81007 54476).  With an estimated bwlch height of c 228m adjoined to the higher of the two tops it meant that this hill had an estimated drop of just less than 30m.  My aim today was to survey the critical bwlch and determine if the hill had sufficient drop to be classified as a P30 Twmpau.

I parked on a muddy grass verge beside where a track heads north-west bisecting the hills of Dinas Mawr (SH 808 539) and the southerly of the two previously twin tops, which is the higher 257.6m summit by Trimble survey. 

The track was awash in mud, and although I left it almost immediately following where a footpath heads north on the map, the underfoot conditions didn’t improve, as cattle had stomped their way through this land and the ground was churned and boggy.

My route took me toward where the map indicated a Chambered Long Cairn is situated, the ground was muddy and wet and the going was slow, albeit the distance between where I left my car and the position of the bwlch is not great.  I had difficulty following the footpath on the ground and had to clamber over one wall.  As I approached the area of the bwlch reed grass swan away across the land, indicating the whole area to be bog bound.  Crossing this land is a track, which again was very muddy, that connects the farm of Ty’n-y-coed with that of Graeanllyn.

I took two data sets, one from the low point of the track as it crossed a stream which gurgled its way south.  To the immediate north of the track was a swamp of oozing mud which was almost level with it, whilst the stream on the southern edge of the track was 0.91m lower than it.  This indicated that the track had in effect almost damned this part of land, and although the water flowed under the track, it seemed the land to its north had been partly turned in to a quagmire, and after gathering a data set on the track, it was this land I now headed in to.

Gathering data from the low point of the track

Thankfully patches of green heaven were interspersed amongst copious amounts of standing water as I ventured in to the delights of the reed grass.  I chose a spot where I could safely position the Trimble on top of my rucksack without each being sunk and lost in the bog of standing water.

Gathering data at the critical bwlch of Gallt y Celyn

After five minutes of data were collected I switched the Trimble off, packed it away and retraced my steps out of the bog and across the mud splattered land to my car.

The fourth and last place I wanted to visit during the remaining daylight hours was to the south of Wrexham, and so an approximate hour’s drive was ahead of me, and with it now being past 2.00pm I could not linger.  


Survey Result:


Bwlch Height:  227.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 81548 54426

Drop:  30.1m (converted to OSGM15) (200m Sub-Twmpau re-instated as Twmpau)

Dominance:  11.68%



For the post detailing the summit survey of Gallt y Celyn please click {here}

For further details please consult the Trimble survey spreadsheet click {here}





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