Tuesday, 25 November 2014

Mapping Mountains – Trimble Surveys – Moelwynion

21.11.14  Pt. 87.3m (SH 607 398), Ynys Berfedd (SH 599 398), Ynys Glog (SH 596 398) and Ynys Gron (SH 596 392)  

Ynys Glog (SH 596 398)
When in the early 1800’s the earthen embankment, now known as the Cob, was built to re-claim land from the large tidal estuary of the Afon Glaslyn, the land of Traeth Mawr which up until then was flooded at high water, was left as flat land used by local landowners for agricultural purposes and grazing.  These flatlands of Traeth Mawr are punctuated by drainage dykes and forested islands that spring up from the flat plain.  It was some of these islands that are connected to the higher peaks of the Moelwynion we wanted to visit.

For more detail relating to Traeth Mawr and the landlocked islands please refer to Aled Williams’ article The Islands of Traeth Mawr.  

In February of this year I’d met Aled and we had visited three of these landlocked islands and found them challenging with overgrown undergrowth, overhanging cliffs and a beauty all to themselves, they seemed a hidden other world, seldom visited and yet full of interest.

Today Aled suggested a circular walk with the possibility of visiting five of these islands.  We parked close to a road junction next to houses at SH 605 388 and walked north-west up the road to where a footpath heads north-east following the course of the railway line.  By now the forecast rain had started and throughout the day it remained, with occasional periods where the wet stuff would relent, teasing us that it had ended.

The first of the day’s islands is positioned at SH 610 396 and has an 81m spot height on the Ordnance Survey 1:25,000 and enlarged Geograph map, unusually there is a five metre difference in height compared to the 1:50,000 map which has an 86m spot height for the island’s high point.  As we approached the sound of forestry workers and their accompanying diggers and tree fellers rang out from the wooded slopes, we soon decided to bi-pass this island as it could wait for another, quieter day.

The footpath headed north to the attractive Ty-fry where the occupant was quick to see us, he soon asked if we had seen the warning notices relating to the tree felling.  A rather humorous discussion then developed between us trying to explain that we had not, and him insisting that we must have.

After our brief encounter we were left in peace to investigate a small corner of the land above Traeth Mawr.  The first island we visited is unnamed on Ordnance Survey maps and as I don't know an appropriate name either locally or historically for it, it is being listed by the point (Pt. 87m) notation.  My recollection of our previous island walk was that they are well protected upthrusts of rock with bramble, small trees, bracken and scrub undergrowth making uphill progress interesting.  The first of the day’s islands was similar as it swept us up in its clutches.  Forward progress was pathless and consisted of finding a route past a small rock terrace to the high part of the hill.

Heading up the small rock terrace on our way to the high point of Pt. 87m
As we crested the upper ridge the rain had stopped leaving in its place a monochrome stillness only punctuated by the late autumnal rusts of bracken and leaves.  The high point was easy to find and as the Trimble gathered its data we looked out onto the flat lands as they extended toward Moel y Gest.

Gathering data at the summit of Pt. 87m
Our next objective; Ynys Berfedd was due west with an intervening bwlch between, this I wanted to survey.  We stumbled through the undergrowth down to a track which led us toward the bwlch which was positioned on a narrow track with steep island slopes of rock on one side.  The Trimble took an age to attain its 0.1m accuracy before data can be logged, but it eventually did, and the customary five minutes of data were gathered and stored.

Gathering data at the critical bwlch of Ynys Berfedd
From the bwlch we clambered over a fence and into the undergrowth of Ynys Berfedd, our next wee island.  Ahead was a moss strewn lump of rock well protected by small trees.  Again progress was interesting and as the high point was neared so the drop immediately to the north increased.

The initial ascent of Ynys Berfedd
The high point proved to be a small pointed rock immediately over a vertical drop down to trees and oblivion, not a place to slip.  Aled devised an ingenious surveying method where the Trimble could be attached to his rucksack which lay neatly beside the high point.  This enabled its internal antenna to be aligned to the high point of the hill but remain safely strapped to the rucksack and even though it was perched on a small pointed rock it would not topple into Trimble hell as the rucksack would hold it firmly in place.

Balanced over another big drop the Trimble gathers data from the top of Ynys Berfedd

Clipped onto Aled's rucksack which nestled safely away from the drop, the Trimble could live for another data gathering day
When the Trimble was gathering data we disappeared into a vegetated morass of trees, rock and bramble and waited for it to gather five minutes of data.  Once stored it was safely unclipped and quickly put back in its holder before we headed down towards the Afon Glaslyn and more undergrowth mayhem of our next island; Ynys Glog.

Thankfully the high point of Ynys Glog was free of trees and consisted of moss on a rock which, although close to a big drop, was not directly over it.  Although similar in nature each island has its own intimate character, as a whole they form a unique landscape for Wales, with their rock upthrusts and undergrowth adding entertaining interest.

Gathering data at the summit of Ynys Glog
We backtracked from the summit to the connecting bwlch which is on a narrow lane beside a house, once the Trimble had done its stuff we left the confines of rock, tree and bramble and headed south on a footpath into the openness of green flatland.  Looking back Ynys Glog looked rather dramatic as it literally shot up from the flat plain as an uncompromising rock edifice.

Gathering data at the critical bwlch of Ynys Glog

These islands are well protected, Ynys Glog from its critical bwlch

Ynys Glog is an upthrust of rock rising from the flat plain of Traeth Mawr
The footpath led towards our last objective of the day; Ynys Gron which at one time was the highest island in these parts.  Old maps show the top with a 323ft / 98m summit.  This has long gone as the Garth Quarry has now obliterated the old natural high point.  However, what remains had been on the agenda for a number of months and coupled with a survey of its critical bwlch may elevate the hill back into the ranks of P30.

Our visit was clandestine as the quarry is still operating.  We headed up through a mass of brambles and trees with Aled leading the way, nearing the top he went ahead and looked over the parapet and came back and said that the high point was just over the lip of quarry spoil that we were now standing on.  This spoil is steep and compact, we edged our way up and looked onto a relatively flat summit area with a small and easily distinguishable high point; beyond was an open expanse of hill nothingness, now the inner workings of the quarry.  We quickly crept back down the steep spoil and I switched the Trimble on and once the file had been created I sneaked back up, placed it on the high point, activated it to attain its accuracy and quickly disappeared out of sight of the quarry.  A couple of minutes later and I crept back up and pressed ‘Log’ and then disappeared out of view.

Gathering data at the high point of Ynys Gron
During this Aled investigated the adjoining land at the edge of the quarry spoil, thankfully blasting was not taking place but the quarry vehicles below could be heard.  Once five minutes of data were collected we shot up to the high point and took a few photographs, we were now in full view of anyone still working in the quarry.  As dusk was setting in and as the diggers below had now stopped we decided to have a look around the upper part of the hill and took another data set from a lower point that was more overgrown.  Once the data from this point had been stored we sped down through the undergrowth to the bwlch.

The remains of Ynys Gron is overshadowed by the Garth Quarry
When we arrived at the bwlch it was dimly lit with the last vestiges of light from a late November afternoon.  The bwlch was narrow and confined with a large wall and trees overshadowing it.  Eventually the Trimble was placed on the wall above the bwlch and an offset of 1.5m measured.  By the time it had stored its data it was dark and raining heavily.

At the very wet and very dark critical bwlch of Ynys Gron
We descended by torch light and got soaked as we made our way down the track from the bwlch onto the road which led back to the car.  There are more of these islands to investigate and I can’t wait to do so as they are proving ideal winter expeditions.  Once back at the car we revised our planned walk up Moel y Dyniewyd for tomorrow and decided to investigate some more of the islands of Traeth Mawr.   

Survey Result:

Pt. 87.3m 

Summit Height:  87.3m (converted to OSGM15)
Summit Grid Reference:  SH 60724 39845

Drop  c 38m 

Dominance:  43.51%

Ynys Berfedd 

Summit Height:  42.9m (converted to OSGM15)
Summit Grid Reference:  SH 59943 39865

Bwlch Height:  6.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 60150 39921

Drop  36.1m (30-99m Twmpau status confirmed) 

Dominance:  84.06%

Ynys Glog 

Summit Height:  40.6m (converted to OSGM15)
Summit Grid Reference:  SH 59647 39826

Bwlch Height:  7.9m (converted to OSGM15)

Bwlch Grid Reference:  SH 59718 39838

Drop  32.7m (30-99m Twmpau addition confirmed) 

Dominance:  80.44% (Dominant addition confirmed)

Ynys Gron 

Summit Height:  69.4m (converted to OSGM15)
Summit Grid Reference:  SH 59653 39268

Bwlch Height:  44.3m (converted to OSGM15)

Bwlch Grid Reference:  SH 59839 39297

Drop  25.1m (30-99m Sub-Twmpau status confirmed and Dominant deletion confirmed)

Dominance:  36.12%

For further details please consult the Trimble Survey Spreadsheet


No comments: