Monday, 10 August 2015

Mapping Mountains – Trimble Surveys – Moelwynion

16.06.15  Pt. 649.8m (SH 660 452)  

Pt. 649.8m (SH 660 452)

Thankfully John set a steady pace as we left the confines of Cwm Croesor and walked up the track to the old disused Croesor Quarry.  Our destination was a hill that until 1998 had not appeared in any list, this was soon rectified when I spotted it whilst on a walk around the Moelwynion, a few minutes later I had surveyed it with my old staff and found that it had approximately 50ft (15.2m) of rise from its critical bwlch to the high point of the rock on its summit.  This hill was then duly surveyed by Dewi Jones, Joe and Tara Nuttall and finally John and Anne Nuttall.  During this time I also surveyed it on two other occasions.  It was duly added to the Nuttalls list under the invented name of Moelwyn Mawr North Ridge Top.  This is not a name I would advocate as research conducted locally will give a name to it, as will historical research, but these more appropriate names will have to wait for another day when the book that Aled and I hope to produce is published, or when the Ordnance Survey apply an appropriate name to this and other hills that are currently unnamed on their maps.

With one of my old measuring staffs at the summit of Pt. 649.8m

Heading up the track toward the abandoned Croesor Quarry

With John setting a reasonable pace it meant that I could keep up with him and Graham, but I was still unable to talk much of the way and did a lot of huffing and puffing.  The blue sky of this morning had been quickly replaced with cloud that pushed its way westward and blew across Cnicht, which looked dramatically large with its steep scree laden south-eastern flank showing itself below the enveloping mist.

The cloud enshrouded Cnicht

The track we were on led to the abandoned Croesor Quarry, what is on view is a tiny part of this once thriving quarry, as its main operation and link to the nearby Rhosydd Quarry was underground and once functional.  Before leaving the track and heading up to our hill, Graham had a look into the entrance to the underground workings, this gave me time to rest and get my breath back as although the mist and cloud skimmed across the hills indicating that conditions on top would be a bit blowy, the warmth of mid-June was pervading our ascent and copious amounts of sweat was bubbling from my forehead.

Nearing the abandoned Croesor Quarry

Leaving the track and abandoned quarry we picked up the continuation of a path up the hill which soon turned to a sheep track, at this point we branched uphill direct for our surveying objective which loomed ahead showing its steep rock strewn southern side.  All around the higher hills were obscured as the cloud enveloped the land and by the time we had reached our objective the wind blew and the murk descended.

Leaving the track a vehicle path on the open hillside soon gave way to a sheep track

Graham heading for the summit

Within a few minutes we had all put on extra layers of clothing as we planned on being on the hill for a number of hours as we were going to line survey it and get GPS data from its summit and bwlch.

We started at the summit and pinpointed the highest part of the summit rock, we then took the equipment down to the bwlch and each one of us in turn estimated where we thought the critical bwlch lay and placed a yellow flag in our chosen spot.  We then placed a number of flags at intervals across the area of the bwlch in a valley to valley and a hill to hill direction.  By using a level and staff we then narrowed the area of the critical bwlch down to a square metre, and once we had taken readings within this small space of land the critical bwlch had been found, and hay presto my yellow flag was proudly flapping in the wind on it – YYIIIIPPPPPP!!!!!!  Mind you John’s estimation of where the critical bwlch lay was only 3mm in height different to its actual position, but Graham was way off and had positioned his flag about 1.5 metres away in distance from the position of the critical bwlch and a few centimetres higher than it.

The view from the summit as Graham pinpoints the highest rock

Once the bwlch had been found we inserted a surveyor’s bolt in the ground with a spare lace around its base to help us get it back out of the ground.  We could now start the line survey with Graham operating the level, John in charge of noting the readings and me operating the staff.  As we proceeded up the hill it got chillier and chillier and the mist blew across the bwlch with large gaps occasionally appearing showing rising land toward Moelwyn Mawr and the great carved out gash between us and the shapely profile of Moel yr Hydd.

John doing the sums

The shapely profile of Moel yr Hydd

Bit by bit we made progress with John giving a running total of overall ascent, as we got nearer the summit we all thought that the running total was indicating that this hill did not have sufficient rise to qualify it for a P15 list.  As the last reading took place with me perched on top of the summit rock, John did the calculations and said that it had only got 14.768m of drop, it had failed – oh bum!  I wonder what John and Anne are going to think about this?

Although Graham had failed miserably to pinpoint the bwlch having been all of 1.5 metres from the designated point, he succeeded in being the closest in his estimation of the hill’s drop value, both he and John estimated that the hill did not have the required 15m of drop, whilst I failed miserably with my estimation as I had guessed a drop value of 15.05m.

So this hill is now relegated to the ranks of sub-P15s, but it is still a worthwhile expedition, similar in some ways to Knight’s Peak, albeit a bit lower in elevation and not quite as buttock clenching to get to its summit!

We now wanted a closing error so we repeated the line survey but this time back down from summit to bwlch, this came to 14.765m, which gave a closing error of 3mm, this result is extremely good.

With the line survey completed John and Graham headed back to the summit to position the Leica GS15 over the summit block, whilst I set the Trimble up at the bwlch to gather five minutes of data.  Once the Trimble had done its stuff I rejoined my two surveying comrades and we huddled down just below the summit rocks in a well sheltered spot.  Much of the next hour was spent chatting about hill related subjects, as time progressed I lay flat with the curvature of the ground fitting snugly against my back and I could have easily dropped off to sleep.  As I occasionally opened my eyes and peered up I could see the orb of the sun peering back down through the mass of swirling cloud, this would be quickly vanquished as the grey cloud mass accelerated its western journey and we would be plunged back into mist.

Gathering data at the critical bwlch with the Trimble, whilst John and Graham position the Leica GS15 over the summit

Graham and John beside the Leica GS15 at the summit

After an hours data had been collected by the Leica GS15 John and Graham took it down to the bwlch and set it up over the surveyor’s bolt whilst I positioned the Trimble on the high point of the hill and gathered five minutes of data, once the Trimble was packed away I descended to another sheltered spot and joined John and Graham for another hour’s wait. 

Gathering data at the summit with the Trimble

The hours wait seemed to go quickly as more hilly related chat was had, and soon it was time to pack up, strip off the extra layers of clothing for the descent and to retrace our steps back down the hill.

The Leica GS15 set-up position at the bwlch
Homeward bound

Survey Result:

Pt. 649.8m

Summit Height:  649.7m (converted to OSGM15, Trimble GeoXH 6000) 

649.8m (converted to OSGM15, Leica GS15)

Summit Grid Reference:  SH 66096 45255

Bwlch Height:  634.8m (converted to OSGM15, Trimble GeoXH 6000) 635.0m 

(converted to OSGM15, Leica GS15)

Bwlch Grid Reference:  SH 66085 45195

Drop:  14.9m (Trimble GeoXH 6000) 14.8m (Leica GS15) Line Survey (14.8m) 

(Uchaf reclassification to 500m Sub-Uchaf and Nuttall deletion)

Dominance:  2.27% (based on Leica GS15 summit height and line survey for 


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

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