Monday, 8 May 2017

Mapping Mountains – Trimble Surveys – Arenig

08.04.17  Drum Boeth (SH 717 464), Drum Boeth (SH 720 462), Moel Bowydd (SH 717 472) and Moel Bowydd (SH 712 470)

Moel Bowydd (SH 712 470)

A day spent in the glorious sunshine with Aled above Blaenau Ffestiniog visiting four 500m P15 hills, three of which only recently entered the listing and tentatively entitled Yr Uchafion through LIDAR data analysed by Aled.

We parked on the main road leading to the centre of town and headed steeply up a narrow street to a gate giving access to a path that climbs beside the south-eastern limits of the piles of slate debris that, and probably forever more, decorate the hill sides above the town.

Leaving the main path we followed a sheep track up toward a prominent level which was positioned just below our first hill of the day.  The blue sky shimmered from above and cast a slight heat haze upon the land, and with the forecast set fine for the day we had no real urgency for the hours ahead, just visit the four hills and survey each summit and bwlch in turn and anything else on the way that looked as if it also needed Trimbling.

Aled on the path above Blaenau Ffestiniog with the higher Moelwynion in the background

Part of our first hill of the day - Drum Boeth (SH 717 464)

It was good to be out with Aled as it had been a number of months since our last walk.  As we neared the first hill; Drum Boeth, the ground below gaped out in a huge chasm that left a slender grassed ridge leading toward our first summit which pinnacled its way upward over an almighty drop.  The whole inner part of the hill had been quarried leaving two distinct high points, the first high point proved a spectacular place to set the Trimble up, and both were surveyed.

Aled on the first point that was Trimbled and which proved to be the lower summit of Drum Boeth (higher summit at SH 717 464)

Gathering data from the summit of Drum Boeth (SH 717 464)

Below us to our east lay the hill’s connecting bwlch, and with the Trimble used as a hand-held GPS it directed us to the LIDAR position that Aled had previously determined.  This was beside Llyn y Drum Boeth and proved a pleasing place to rest whilst the Trimble gathered its customary five minutes of data nestled on top of my rucksack, which is used as an improvised tripod and gives elevation for the surveying equipment above its immediate surrounds.

Llyn y Drum Boeth and the critical bwlch of our first hill with the Trimble gathering data atop my rucksack

Drum Boeth (SH 717 464) with Cnicht in the background on far left and Allt Fawr in the central background

Our next objective was a hill on the continuing ridge of Drum Boeth, and one that I had previously surveyed in October 2005 using a basic levelling technique, the resulting surveyed drop on that day was 48ft 6″ (14.8m) which was one of the closest drop values to the minimum of 15m required to qualify for the 500m P15 list.  Aled has subsequently analysed this area using LIDAR data and this hill is now instated as an Uchaf with 15.1m of drop, and we were both looking forward to the comparison between this drop value and that produced by the Trimble.

The summit was easy to distinguish and soon the Trimble was gathering data, once 300 datum points were collected we proceeded down to the hill’s connecting bwlch and marched back and forth trying to pinpoint the position for Trimble placement, once the position had been agreed another five minute data set was gathered.

Gathering data from the summit of Drum Boeth (SH 720 462)

Gathering data at the critical bwlch of Drum Boeth (summit at SH 720 462)

It was proving such a fantastic early spring day that after packing the Trimble away we contemplated heading toward Foel Fras and Moel Penamnen, but decided that they could wait for another day, and therefore we left the bwlch of Drum Boeth and headed north to the track on the southern shore of Llyn Bowydd, a beautiful lake, today it was coloured deep blue with flecks of rippled water edging over its expanse.

Llyn Bowydd and the slither of Llyn Newydd with Moel Penamnen in the background

Ahead of us lay the last two hills of the day which are both a part of Moel Bowydd, leaving the track we headed over moor grass toward the summit of the higher of the two hills and only encountered heather towards its top.  Again, pinpointing the summit was relatively easy and soon the Trimble was up and running quietly beeping away collecting its 300 allotted datum points.

Gathering data at the summit of Moel Bowydd (SH 717 472)

I wasn’t looking forward to the next part of the walk as it was a there and back to the hill’s connecting bwlch through what I remembered as torturous heather, it’s funny how sometimes the mind can over exaggerate as the going proved relatively easy, albeit pathless, with problems only arising at the bwlch which proved to be boggy, expansive and relatively flat.  We came away with two data sets, 100 metres or so apart which should give adequate data for the value of this hill’s drop. 

A lovely wild area to gather data from - the bwlch area of Moel Bowydd (summit at SH 717 472)

Whilst retracing our steps back toward the last summit and onward to the connecting bwlch with the last hill of the day, which is also named Moel Bowydd, we watched people fly down the zip wire in the Llechwedd Quarry, zooming down at increasing speed until they disappeared out of view behind a large mound of slate.

The last bwlch of the day proved relatively small in area and soon the Trimble was positioned atop my rucksack gathering data, just one summit remained and again it was relatively easy to pinpoint at the end of a grassed ridge.

Gathering data from the last bwlch of the day which is adjoined to Moel Bowydd (summit at SH 712 470)

Gathering data from the last summit of the day - Moel Bowydd (SH 712 470)

Our descent route proved fun as the track we followed petered out amongst one of the huge slate mounds that predominate these hillsides, and as we neared the end of what was relatively easy but nonetheless steepening ground the remainder of ground shot downward, unless we backtracked uphill this seemed to be our only option, I didn’t fancy this as it looked decidedly dodgy, especially with a wonky right knee.  Whilst Aled threw a few pebbles down the steep slope and watched then bounce to the bottom, I investigated further along the edge of the slate mound and found what looked to be a reasonable way down; I waved toward Aled signalling for him to join me.  Once beside me he skipped up to safer ground whilst I became marooned on the edge of oblivion trying my utmost to get purchase on the steep slate pile, a helping hand from Aled did the trick and we happily continued our descent route back into Blaenau.

Contemplating a steep descent

Survey Result:

Drum Boeth

Summit Height:  506.8m (converted to OSGM15)

Summit Grid Reference:  SH 71724 46417

Bwlch Height:  490.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 71823 46452

Dominance:  3.24%  

Drum Boeth

Summit Height:  523.4m (converted to OSGM15)

Summit Grid Reference:  SH 72020 46289

Bwlch Height:  508.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 72159 46335

Dominance:  2.91%  

Moel Bowydd

Summit Height:  510.0m (converted to OSGM15)

Summit Grid Reference:  SH 71781 47285

Bwlch Height:  494.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 71938 47753

Drop:  15.9m (Uchaf status confirmed)

Dominance:  3.11% 


Moel Bowydd

Summit Height:  500.5m (converted to OSGM15) (Uchaf status confirmed) (significant height revision)

Summit Grid Reference:  SH 71272 47051

Bwlch Height:  482.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 71603 47208

Dominance:  3.62% 


No comments: