Mapping Mountains – Trimble Surveys – Mynydd Hiraethog

05.04.16  Foel Las (SH 886 686) and Foel Las (SH 894 687)  

Foel Las (SH 894 687)

As the next installment of the Dominants is to the range of hills of Mynydd Hiraethog I wanted an appropriate photograph of Foel Las to accompany the introduction to this group of hills, therefore with the weather set fine I headed to north-west Wales. 

LIDAR image of the two Foel Las summits at SH 886 686 and SH 894 687

I left my car parked on the B 5832 close to a converted Chapel at SH 889 669 and headed toward a track where the critical bwlch for the higher of the two Foel Las summits is positioned.  The forecast for the day was good with mainly dry conditions with sunshine in the morning and build-up of cloud in the afternoon.

After assessing the lay of land on and around the track I positioned the Trimble on top of my rucksack and waited for the 0.1m accuracy level to be attained before pressing Log.  As data were gathered I stood an adequate distance away from the equipment and examined the map before looking up at the higher of the two hills I planned on visiting.  Between the two hills was forestry which wasn’t marked on the Explorer map I have, and having previously looked at online mapping there were also a number of small lakes now situated around the area of the bwlch between the two hills; there had obviously been a lot of work done in transforming the land around these hills with a number of tracks also indicated on online mapping leading to the small lakes.

Gathering data at the bwlch of the higher of the Foel Las summits

Once data were stored I packed the Trimble away and walked back to the road, past my car and up a minor lane toward a public footpath, I followed this, or at least I thought I had, until branching out over a number of fields aiming for a track which headed toward the summit of the lower of the two hills.  In hindsight I should have continued on the minor road for another 100 metres which would have given me direct access to a track which headed straight for the summit of my first hill.

As I walked over a field toward the track a vehicle pulled up, I headed toward it and spoke with the driver, I asked if she minded me using the track to visit the hills, she explained that she wasn’t the land owner and had been invited there for the day.  We chatted about the development on the hill, including the forestry.  I left having thanked her and she smiled back at me as I waved my good byes and continued up the track.

As I gained height a chilling breeze blew and I put my thin £5.00 gloves on which kept my fingers functional.  Off in the distance was the sound of a tractor which came in to view as I rounded a corner of the track, it was above the forestry moving back and forth high on the hill, also now in view were a number of small lakes, each positioned hugging the landscape and blending in to the environment.

A pair of Canada geese on one of the small lakes below the summit of Foel Las (SH 886 686)

The track I followed continued away from the lower Foel Las summit so I squelched my way across a wet field and headed up to where the tractor had been busy doing what tractors do.  By the time I came across its tracks it had moved on to another part of the hill which left the summit area quiet except for scampering lambs which suckled their mothers.  The high point was easily identifiable and soon the Trimble was aligned with it and gathering its customary five minutes of data.

Gathering data at the summit of Foel Las (SH 886 686)

The higher of the two Foel Las summits (SH 894 687)

Heading east from the summit toward the higher hill I walked down to the connecting bwlch which now has a small forestry plantation on it, this can be easily bi-passed on its northern side, as I headed that way I noticed a gate close to the edge of the higher of two lakes, this gave access to a track which cuts through beside the trees and which seemed to form the critical bwlch for the lower Foel Las summit.  Deciding to leave this bwlch survey until later I headed up to the higher summit.

The summit comprises a number of bumps, many positioned on small outcrops of rock.  I decided to survey three points, two of these points being a few metres from one another and which were positioned on the same bump, whilst the third was about 40 metres away and close to where the 320m ring contour appears on Ordnance Survey maps.  As these data sets were gathered I looked west toward the high Eryri peaks and watched as the cloud slowly ripped itself away from their ridges.

Gathering data at the higher summit

Just one survey remained on this first walk of the day and that was back at the connecting bwlch between the two hills.  I left the higher summit and wandered back to the track beside the small plantation of conifers.  Finding its low point on the valley to valley traverse proved relatively easy and I positioned the Trimble on top of my rucksack having measured a 0.41m offset between its internal antenna and the ground below.

As the Trimble’s accuracy level slowly ebbed down to 0.1m I waited beside the gate and let my mind wander to all manner of things.  Every five minutes I scampered back to the equipment to check on its downward accuracy progress, it took over fifteen minutes for the 0.1m accuracy level to be attained and once it had I quickly pressed Log and headed back to the gate for another five minute wait.

Gathering data at the critical bwlch of the lower Foel Las summit

The higher Foel Las summit from the small lake positioned near to the bwlch between the two hills

Once data were gathered and the equipment packed away I investigated the lay of land inside the forest and to its north, it was hard to judge where the exact bwlch lay as the tree coverage was not ideal for such a thing, but the ground looked as if it was constantly rising toward where the track is positioned.  Happy that I’d done all I could I headed toward a near track which connected with my inward route and which I followed down to the minor lane and my car.

Survey Result:

Foel Las (significant name change)

Summit Height:  307.1m (converted to OSGM15)

Summit Grid Reference:  SH 88690 68624

Bwlch Height:  276.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 88939 68659

Drop:  30.9m

Dominance:  10.05%

Foel Las (significant name change)

Summit Height:  319.8m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 89473 68747 (Trimble GeoXH 6000)

Bwlch Height:  202.6m (LIDAR)

Bwlch Grid Reference:  SH 89078 67030 (LIDAR)

Drop:  117.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  36.64% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

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