Mapping Mountains – Trimble Surveys – Moel Siabod

11.03.18  Garreg Amlwg (SH 717 549), Moel Siabod (SH 705 546), Pt. 815.9m (SH 708 550), Pt. 811.2m (SH 709 551) and Pt. 800.8m (SH 711 552)

Garreg Amlwg (SH 717 549)

For many years it seemed as if I was walking with blinkers on, being preoccupied with the 2,000ft mountains of Wales with little regard for visiting lower heighted hills.  Nowadays I get pleasure enough on the lower P30s, but when opportunity arises to visit the higher hills their dramatic architecture is savoured, and today was such an occasion as along with Mark and Aled we planned on visiting Moel Siabod and a number of lower satellite peaks whose existing and potential P15 status needed clarifying.

Moel Siabod is a wonderful hill set apart from its higher neighbours, its 872m map heighted summit commands extensive views and is a relative recent addition to Mark’s P600 Majors list, only entering this list as the 272m bwlch spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website gives the hill 600m of map spot heighted drop.

Having left three cars at different points for optional descent routes we ascended via Pont Cyfyng, walking up the narrow lane to the footpath gaining the track leading to the north-eastern ridge of Moel Siabod, across the valley spring sunshine picked out the rugged profile of Creigiau Gleision and the pyramidal shape of Pen Llithrig y Wrach.  However, the sunshine was not to last as high greying cloud would slowly ebb in from the south adding wisps to the higher tops with the prospect of incoming rain.

Creigiau Gleision

Pen Llithrig y Wrach

The first hill we wanted to investigate is listed as an Uchaf, these are the Welsh P15 hills at and over 500m in height, and the hill only entered this list through a basic levelling survey conducted in July 2004.  Following a path toward a quarry lake the hill rose above slightly rounded and elongated in profile it sits away from its much higher neighbour and is probably seldom visited and yet it is situated in a marvellously wild landscape of heather moor, bog and rock.

Moel Siabod looked dramatically appetising as we descended to the hill’s connecting bwlch which has a number of small attractive pools situated on it, we judged where the critical bwlch lay and as I set the Trimble up and floundered in the overly wet bog adjacent to the larger of these pools, Mark and Aled headed off to investigate if there was an outflow from the opposing side of the pool.

Descending to the connecting bwlch of Garreg Amlwg

Mark with Moel Siabod as backdrop

Gathering data at the area of the bwlch of Garreg Amlwg

This hill has two tops and both were Trimbled, with each summit consisting of a large rock.  As the more north-westerly top was Trimbled Mark and Aled visited the south-easterly one, I looked out as they waited on this summit with the cliff face of Moel Siabod as backdrop rising skyward dwarfing our position.

Gathering data from what proved to be the lower of the two tops

Aled and Mark on the south-westerly top of Garreg Amlwg

Gathering data from the summit of Garreg Amlwg

Leaving the hill we followed a narrow path across the outflow from Llyn y Foel and joined the lower part of Daear Ddu, which if wanting a scramble is the way to approach Moel Siabod.  Daear Ddu is the eastern ridge of Moel Siabod and I’ve enjoyed its rock on many occasions, the first being with a horrendous hangover when I was sick on the hill, not a pretty sight!

Beside Llyn y Foel

As height was gained the view opened, down upon Llyn y Foel and across the Eryri peaks to the far off Berwyn and Bryniau Clwyd.  The ridge was fun, as it ever is, with just enough hand on rock to bring a sustainable amount of enjoyment.

Llyn y Foel

The north-eastern ridge of Moel Siabod with the three tops which were later surveyed

By the time we crested the summit ridge cloud had built and as the Trimble clung aligned to the highest rock gathering its all-important data, mist quickly rolled in and would remain with us until we descended.

The north-eastern ridge from close to the summit of Moel Siabod

The view south-west just before the mist rolled in

Gathering data at the summit of Moel Siabod

If time permitted we hoped to survey at least two of the three tops on the upper part of the north-easterly ridge of Moel Siabod, each is a jumble of rock with two of the three bylchau being tight with plunging drops nearby down horrendously steep gulleys.

After the Trimble had gathered its allotted data from the summit of Moel Siabod I joined Mark and Aled in the large wind shelter just below the high point for a bite to eat before continuing to the three rocky tops. 

As we walked through the mist toward the first connecting bwlch we discussed the merits of what ones to survey as dusk would be approaching on our descent and as the weather had closed in it looked as if the forecast rain would overtake us, these weren’t ideal conditions to survey castellated summits above mighty drops.  The impending problem was solved when Aled suggested a two minute data set at each bwlch and summit, this is the minimum suggested for data collection by Trimble.  This would enable the three tops to be surveyed in turn and would complete all tops adjoined to Moel Siabod then having been Trimbled.

The ridge proved fun as the rock was damp with rock step after rock step negotiated from one summit to bwlch and onward to the next summit.  These surveys came thick and fast with barely a moment to contemplate some of the Trimble bwlch positions with two being on the edge of mountainous drops down steep gulleys.

A precarious position for a Trimble

As the last summit was Trimbled Mark headed down to a fence which gave access to the path leading to where one of our cars was parked beside Plas y Brenin and Llynnau Mymbyr, Aled and I soon followed.

Gathering data  from the summit of Pt. 800.8m

It had been a good day on the hill with ten surveys completed, with an enjoyable time picking out an occasional scramble whilst visiting the summit of one of Eryri’s special mountains.  We ended the day in the Bryn Tyrch at Capel Curig with good conversation and a welcome meal.

Postscript:  Since the survey of these hills, the LIDAR (Light Detection & Ranging) technique is now being used to produce accurate height and position for hills.  Therefore, numerical data produced by surveying with the Trimble GeoXH 6000 is being updated.  However, each individual data set is analysed and as data produced by the Trimble GeoXH 6000 is considered more accurate it is this relative to the position produced by LIDAR that is prioritised.

   

Survey Result:

Garreg Amlwg

Summit Height:  561.6m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 71781 54962 (Trimble GeoXH 6000)

Bwlch Height:  546.5m (converted to OSGM15, Trimble GeoXH 6000 adjusted height relative to LIDAR position)

Bwlch Grid Reference:  SH 71738 55023 (LIDAR)

Drop:  15.1m (Trimble GeoXH 6000 summit and Trimble GeoXH 6000 adjusted bwlch height relative to LIDAR position)

Dominance:  2.69% (Trimble GeoXH 6000 summit and Trimble GeoXH 6000 adjusted bwlch height relative to LIDAR position)

Moel Siabod

Summit Height:  872.2m (converted to OSGM15)

Summit Grid Reference:  SH 70524 54631

Bwlch Height:  272.3m (converted to OSGM15) (from previous Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SH 66044 55603 (from previous Trimble GeoXH 6000 survey)

Drop:  599.9m (P600 Major deletion)

Dominance:  68.78%

Pt. 815.9m

Summit Height:  815.9m (converted to OSGM15)

Summit Grid Reference:  SH 70859 55036

Bwlch Height:  808.9m (converted to OSGM15)

Bwlch Grid Reference:  SH 70797 54991

Drop:  7.0m

Dominance:  0.86%

Pt. 811.2m

Summit Height:  811.2m (converted to OSGM15)

Summit Grid Reference:  SH 70955 55120

Bwlch Height:  803.9m (converted to OSGM15)

Bwlch Grid Reference:  SH 70898 55084

Drop:  7.3m

Dominance:  0.90%

Pt. 800.8m

Summit Height:  800.8m (converted to OSGM15)

Summit Grid Reference:  SH 71115 55231

Bwlch Height:  787.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 71076 55224

Drop:  13.3m

Dominance:  1.66%

For details on the 1st bwlch survey of Moel Siabod

For details on the 2nd bwlch survey of Moel Siabod

For further details please consult the Trimble Survey Spreadsheet

Mapping Mountains – Trimble Surveys – Y Mynydd Du

13.06.17  Fan Brycheiniog (SN 824 220, only bwlch surveyed)

Gathering data at the bwlch of Fan Brycheiniog

Standing beside an A road watching cars and lorries thunder past a small piece of surveying equipment could be thought of as an unusual pastime, to many it undoubtedly is, but there is a satisfaction to such a thing, albeit an unusual one.

Having visited Mynydd y Drum and the Nant Helen Opencast Mine and with a small walk above Llanfair-ym-Muallt (Builth Wells) pencilled in for later in the day I thought I’d better survey the critical bwlch of Fan Brycheiniog; one of south Wales’ highest mountains.  This bwlch is positioned on or beside the A 4067 as it heads southward from Sennybridge toward Ystradgynlais, it was a bwlch I drove over earlier in the day and when doing so I tried to judge where its critical point lay.

Thankfully the road has a number of large pull-ins close to the area of the bwlch and once out of my car I went to work.  This work consisted of bending over, kneeling and sometimes lying on the ground assessing where the uphill from the valley to valley traverse meets the downhill from the hill to hill traverse.  When doing this it is advantageous to gain height for an overall view of the scene, unfortunately the ground to the east of the road is steep and therefore I used a conveniently placed ladder stile to stand on top of and gain a little elevation to assess the lay of land.

It proved easy to judge where the upper part of the northern valley lay as the reed grass and wet surrounds of the Blaen-crai was positioned beside the ladder stile, which was only a few metres from the road.  I marched back to the lay-by where my car was parked and proceeded to kneel on the grass verge to look at the uphill part of the road, there seemed to be two points where the high point may lie, with a slight dip in the road between.

I ummed and aghed for ten minutes or so wondering which out of these two points to gather data from, on the eastern side of the road a drainage ditch beside the grass verge helped in judging where the downward southern land lay, however as drainage ditches aren’t necessarily consistent in their depth I decided only to treat this as an indicator of where the critical point may lie.

During this process vehicles sped past, one thing was certain the Trimble was not going to be set-up on the road, perhaps if this bwlch was on a country lane it would be all right to do so, but a busy A road was asking for trouble.  Deciding on my point I set the Trimble up on my rucksack and measured a 0.42m offset between the equipment’s internal antenna and the ground at the base of the rucksack and waited until the 0.1m accuracy level was attained before data should be logged.

The Trimble set-up position at the bwlch of Fan Brycheiniog

During data collection I made a note of how many vehicles whizzed past heading south, the total amounted to eight cars and four Lorries, all within five minutes; hopefully the data set won’t be compromised by this activity.

Once the allotted five minutes of data collection were up, I switched the equipment off, packed it away and headed north to the outskirts of Llanfair-ym-Muallt (Builth Wells) and the joys of Garth (SO 053 506), a hill I’d wanted to visit for many a year.

Postscript:

Since this survey took place the details for the bwlch of this hill have been ascertained from LIDAR analysis conducted by Aled Williams, and these details are being prioritised in favour of those produced by the Trimble GeoXH 6000.

  

Survey Result:

Fan Brycheiniog

Summit Height:  802.7m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 82435 22060 (Trimble GeoXH 6000)

Bwlch Height:  378.5m (LIDAR)

Bwlch Grid Reference:  SN 87056 19547 (LIDAR)

Drop:  424.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  52.84% (Trimble GeoXH 6000 summit and LIDAR bwlch)

For details on the summit survey of Fan Brycheiniog

For further details please consult the Trimble Survey Spreadsheet

Mapping Mountains – Trimble Surveys – Bannau Brycheiniog and Fforest Fawr

25.10.16  Craig Gwaun Taf (SO 005 207), Pen y Fan (SO 012 215), Corn Du (SO 007 213), Y Gurn (SN 988 216) and Fan Fawr (SN 969 193, bwlch only)

Corn Du (SO 007 213)

I’d long wanted to visit the high peaks of Bannau Brycheiniog and Trimble them, and doing so was long overdue.  Having visited these and the other Welsh 2,000ft hills on many occasions, re-visiting them is always a pleasure, especially after time between visits being many years, when this happens it is a clichéd expression to say that it is like visiting old friends, but that is exactly how it feels, as although the hills are inanimate objects they have an uncanny presence that on many occasions can form characteristics seemingly all their own.

As well as wanting to visit the higher peaks of Bannau Brycheiniog there was one particular hill that I was extremely interested in Trimbling, this hill is Craig Gwaun Taf, which is an outlier of Corn Du and thrusts upward on its southerly ridge beyond Bwlch Duwynt before descending south-eastward toward the Pentwyn Reservoir.

Craig Gwaun Taf is given an 824m summit spot height on current Ordnance Survey maps and has bwlch contouring between 800m – 810m, with an 815m spot height on the area of the bwlch on the Ordnance Survey enlarged mapping on the Geograph website.  These figures give this hill an approximate c 13m of drop based on interpolation of bwlch contours, or only 9m of drop if based on the 815m spot height.  However, this hill and many others has recently been checked against LIDAR data by Joe Nuttall, who is the son of John and Anne Nuttall, who are guidebook authors and list compilers to the 2,000ft mountains of both England and Wales, and who have kept me busy on the hills for many a year.

LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales, and Joe has been diligently checking a number of hills for qualification to his parents 2,000ft list.  These lists are based on a minimum qualifying drop value of 15m and Joe found that LIDAR data gave Craig Gwaun Taf a drop of 15.783m, Joe then contacted me and asked if I could Trimble the hill.  By doing so it would give a comparison for this hill between LIDAR data and Trimble data, and confirm the hill’s drop value and unless the Trimble result was within an approximate 0.1m of the required minimum drop value of 15m it would also confirm the hill’s status.

I set off from the car park at the top of the A 470 opposite the Storey Arms at 8.50am, having driven from Worcester, the first time I’d ventured into Wales for a hill walk from the recesses of this remote part of deepest, darkest England.  Although the forecast gave settled, dry conditions with little breeze, the cloud base was low and a murky greyness pervaded the hills.

Deciding that I’d leave Y Gurn until later in the afternoon when its moorland path connecting it to the north-westerly ridge of Corn Du may be visible if the thickened layer of mist broke, as predicted, I walked south-eastward adjacent to the busy road on a gravelled track on the periphery of forestry to the car park at Pont ar Daf, this meant doing the higher peaks first, in mist, but as their paths are broad and their ridges easily discernible, route finding was not a problem.

I’d only been on the path from Pont ar Daf to Pen y Fan a couple of times before, once when cycling and pushing mountain bikes to its summit in 1990 during a ten day expedition mountain biking the hill boundary of Powys, on that day it was progressively getting hotter, which was a contrast to today, where when height was gained, a slight chill pervaded the wisps of mist as they gently rolled through the land.

The path at Pont ar Daf leading toward Craig Gwaun Taf, Corn Du and Pen y Fan

By the time I arrived at Bwlch Duwynt, which is the pass between Corn Du and Craig Gwaun Taf, one person had overtaken me and a few people had headed down the hill after making an early morning ascent, all were either heading toward or coming from Pen y Fan, leaving Craig Gwaun Taf quietly forgotten in the mist, which suited me and the Trimble just fine.

Today the critical bwlch consisted of an elongated, shallow muddy puddle which stretched over the bwlch from the valley to valley direction.  I checked the ten figure grid reference for the bwlch that Joe had given me when he assessed this hill’s drop via the LIDAR data, and chose a position within a few metres of this grid reference for the first of three Trimble positions at the bwlch.  This position was central on the valley to valley traverse and I gathered two five minute data sets from the same position.  I then collected a further five minute data set from either end of the shallow puddle, firstly on its western side and secondly on its eastern side.  These four data sets will give a good value for the height of this bwlch.

Gathering data at the bwlch of Craig Gwaun Taf

Gathering data at the first of three positions Trimbled at the bwlch of Craig Gwaun Taf

Having taken a number of photos I packed the Trimble away and headed to the summit of Craig Gwaun Taf, which I found was the second rise along the ridge when ascending from its connecting bwlch with Corn Du.  The summit consists of a small grassed hummock a couple of metres east of the path, which continues following the course of the hill’s south-easterly ridge.

I placed the Trimble on the high point and waited patiently for it to reach its 0.1m accuracy level before data should be logged, once one five minute data set was collected I switched the equipment off, then switched it back on and repeated the process until another five minute data set was gathered.  I then positioned the Trimble on top of my rucksack and measured a 0.23m offset between the high point of the hill and the Trimble’s internal antenna and waited until another five minute data set was gathered.  These three data sets will give a good value for the height of this hill and when combined with the four data sets taken at its bwlch, will give sufficient data to give Craig Gwaun Taf an accurate drop value and ascertain its status.

Looking north from the summit of Craig Gwaun Taf with the Trimble gathering data

Looking south from the summit of Craig Gwaun Taf with the Trimble gathering data

As I left the summit of Craig Gwaun Taf a number of voices cast from the mist and drifted my way in the slight breeze that occasionally sprang up, and by the time I reached the path toward Pen y Fan a multitude of people were heading in all directions, some downward, others up towards Corn Du and more toward Pen y Fan, I suspected the summit of south Wales’ highest mountain may be a little busy.

Glimpsing Corn Du through the mist

The summit of Pen y Fan once had a trig pillar at its high point, nowadays it has a constructed cairn with an embedded stone marker giving the hill’s name and height, and it also has many visitors who throng to its summit in all weathers.  When I arrived I wondered how on earth I was going to keep so many people away from the high point when the Trimble was gathering its all-important summit data.  Surprisingly this proved relatively easy and I only had to explain to a few people what I wanted to do and all were extremely compliant with the wants of a mountain surveying Trimbling person.

The Trimble holding back the multitude as it gathers data at the summit of Pen y Fan

Having gathered data at the top of the solid cairn I wanted another five minute data set at the highest land at the periphery of the cairn, this again proved relatively easy to obtain. 

Gathering data at the high point on the periphery of the summit cone

Gathering data adjacent to the coned cairn atop Pen y Fan

Leaving the throng of people beside the summit of Pen y Fan I back-tracked to its connecting bwlch with Corn Du, the position of this bwlch proved easy to identify, and within a few minutes the Trimble was balanced over the northern precipice gathering data.

Gathering data at the critical bwlch of Corn Du

My next objective was Corn Du and I hoped that its summit would give a little peace and quiet when compared to that of Pen y Fan, however it didn’t want to be outdone by its higher neighbour and another multitude of people were gathered around its constructed cairn.  This summit also proved relatively easy to survey as everyone gathered around its periphery giving the Trimble time and space to gather its data.  Before heading down the north-westerly ridge of Corn Du I wanted another five minute data set from the highest natural ground remaining on the hill, I judged this to be one of the small grass hummocks on the edge of its very steep northerly drop, I placed the Trimble on it and secured it in place with a few small rocks before pressing ‘Log’ and hoping that it wouldn’t fancy a quick descent in to the cwm 250m – 300m below.

Gathering data at the summit of Corn Du

Gathering data at what I judged to be the remaining 'natural' high point of Corn Du

Once the Trimble was salvaged from its precarious position I plodded down in continuing mist, following the broad path to the obelisk commemorating Tommy Jones, who at the age of five lost his way from Cwm-llwch farm and whose body was found on this spot 29 days later.  I knew that a path went from near this obelisk toward the bwlch and then the summit of my last hill of the day; Y Gurn, but I also knew that the path was relatively narrow and that other paths probably existed heading off in a number of directions.  Finding one that took me onward I happily followed it until it seemed to be heading too far south, I stopped and checked the grid reference in the Trimble against the map and back-tracked across the moor until at the critical bwlch of Y Gurn, by now the misty conditions that had pervaded the hills started to break up and sunlight pierced out from behind the cloud, brightening the land and giving a partly hazed autumnal glow.

After gathering data at the critical bwlch of Y Gurn I followed a good path to its summit and placed the Trimble beside the small cairn that sits atop a peat hagged hummock, once the customary five minutes of data were gathered I followed the path and fence line down to connect with the main path that heads from Storey Arms to Pen y Fan.

Gathering data at the critical bwlch of Y Gurn

Gathering data at the summit of Y Gurn

There were many people on this main path, with the majority heading down to the Storey Arms, but some were heading up in what was proving to be brightening conditions with glimmers of the higher peaks tantalisingly on show as their straight edged ridges gleamed out of the cloud.

Craig Gwaun Taf above afternoon mist with people heading back to the Storey Arms on the main Pen y Fan path

Only one survey remained and that was for the critical bwlch of Fan Fawr which proved to be adjacent to the car park opposite the Storey Arms.  This was on ground next to a ditch which I followed in both directions, and which seemed to be continuous and therefore probably man-made for drainage, because of this I chose a spot that was conveniently on solid ground above the ditch beside one of the duck boards laid across it, once five minutes of data were collected I headed back to my car happy in the knowledge that 15 surveys had been conducted and that the status of Craig Gwaun Taf would be finally determined.

Gathering data at the critical bwlch of Fan Fawr

Survey Result:

Craig Gwaun Taf

Summit Height:  826.4m (converted to OSGM15) (significant height revision) 

Summit Grid Reference:  SO 00548 20720

Bwlch Height:  810.3m (converted to OSGM15)

Bwlch Grid Reference:  SO 00555 20862

Drop:  16.1m (Uchaf addition confirmed and Nuttall addition confirmed)

Dominance:  1.95%

 

Pen y Fan

Summit Height:  885.7m (converted to OSGM15)

Summit Grid Reference:  SO 01208 21582

Bwlch Height:  215.0m (converted to OSGM15, from subsequent Trimble GeoXH 6000 survey to remaining natural bwlch)

Bwlch Height:  209.3m (LIDAR, disused rail cutting)

Bwlch Grid Reference:  SH 93136 00074 (remaining natural bwlch)

Bwlch Grid Reference:  SH 93041 99532 (LIDAR, disused rail cutting)

Drop:  670.7m (cairned summit and remaining natural bwlch)

Drop:  676.45m (cairned summit and disused rail cutting bwlch)

Dominance:  75.72% (cairned summit and remaining natural bwlch)

Dominance:  76.37% (cairned summit and disused rail cutting bwlch)




Corn Du

Summit Height:  872.6m (converted to OSGM15)

Summit Grid Reference:  SO 00718 21332

Bwlch Height:  843.6m (converted to OSGM15)

Bwlch Grid Reference:  SO 00911 21394

Drop:  29.0m (Subsimm and 800m Sub-Twmpau status confirmed)

Dominance:  3.32%

 

Y Gurn

Summit Height:  618.9m (converted to OSGM15)

Summit Grid Reference:  SN 98895 21607

Bwlch Height:  591.5m (converted to OSGM15)

Bwlch Grid Reference:  SN 99173 22100

Drop:  27.4m (Subsimm and 600m Sub-Twmpau status confirmed)

Dominance:  4.42% 
 

Fan Fawr

Summit Height:  734m (spot height)

Summit Grid Reference:  SN 96997 19351 (spot height)

Bwlch Height:  439.5m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SN 98223 20289 (Trimble GeoXH 6000)

Drop:  295m (spot height summit and Trimble GeoXH 6000 bwlch)

Dominance:  40.13% (spot height summit and Trimble GeoXH 6000 bwlch)

 

For details on the 1st bwlch survey of Pen y Fan

For details on the 2nd bwlch survey of Pen y Fan

For further details please consult the Trimble Survey Spreadsheet