Mapping Mountains – Trimble Surveys – Pumlumon

07.09.15  Bryn y Fedwen (SN 840 953 – previously Trimbled), Mynydd Cil Cwm (SN 859 964), Bryn y Fedwen (SN 851 972), Moelfre (SN 848 983), Llannerch yr Aur (SN 863 978) and Banc Bron Derwgoed (SN 871 987)  

Moelfre (SN 848 983)

The architectural form carved out when the glaciers receded in the last ice age left the northern lands of the Pumlumon range of hills with a beauty all to themselves.  These northern lands extend from their higher and better known hills to a cascade of plunging drops and infrequent trodden summits.  It was a part of this northern land that Aled and I wanted to investigate today.

We met in Llanbrynmair in the early afternoon and left one car at the top of a minor road above Cwm Nant Heli at Bwlch Glynmynydd (SN 866 992) and proceeded to drive toward Dylife, only stopping to admire the view down into the bowl of land where the Afon Twymyn flows from the hidden Ffrwd Fawr waterfall.

The Pennant Gorge - sublime as ever

The forecast for the day was excellent with sunshine and a hint of light breeze and as we parked beside the entrance track to the Glaslyn Nature Reserve the colours shone from the surrounding hills. 

Our planned walk was over two Uchafion, with one being a marginal, and three Pedwarau, with two being marginal and the third classified as a Hump with 106m of drop, so there would be lots of scope for status change with all except for our first hill planned to be Trimbled.  This first hill is named Bryn y Fedwen on current Ordnance Survey maps and as I had previously Trimbled it when on a walk with Eryl on 09.01.14 I did not plan to do so again on today’s walk.

Once Aled’s van was parked we were soon on the summit of our first hill which although the highest of the day was certainly not the best.  The continuation of the route headed north-east following the line of a fence, off in the distance a tractor chugged its way up and then down a field where our route was taking us, as we approached, it was on a downward cycle and we didn’t have the pleasure of a chat with a local farmer and just heard the chug, chug as it went about its business.

Aled approaching the summit of the highest hill of the day, named as Bryn y Fedwen on the map

We had a fleeting inspection of the connecting land at the bwlch as we walked toward the summit of our second hill; Mynydd Cil Cwm.  I’d visited this hill once before as a quick there and back from the convenience of a track from the high road where we had parked and remembered its summit to be heather bound, this is a confliction as it was set against reclaimed grazing land with its greenness butting up against the purples and soft feel of hill heather.

Two aspects of Mynydd Cil Cwm - the first from our approach to the summit.....

......and the second shows the western side of Mynydd Cil Cwm above the Pennant Gorge

Once at the summit of Mynydd Cil Cwm two points were surveyed with the Trimble, the first where we judged the high point of the hill to be situated and the second where the 527m spot height on Ordnance Survey maps appears on the ground.

Gathering data at the first of two positions on the summit area of Mynydd Cil Cwm

Gathering data at the second of two positions on the summit of Mynydd Cil Cwm

As the last of the two lots of 300 data points were collected I switched the machine off, took a few photos and we retraced our steps down toward the hill’s bwlch.  This now has a conifer plantation on its eastern side, which is not shown on my old 1:25,000 Explorer map.  The bwlch spot height that appears on the enlarged Geograph map is placed at a meeting of fences, we judged the ground to the north-east of the fence junction to be lower on the hill to hill traverse and I placed the Trimble on top of my rucksack to give it elevation above the ground and set it to gather more data.  By now Aled had descended to the track which wound its way down the northern slopes toward our next hill as this part of land was infested with flying ants, which I didn’t particularly mind until one bit me.

Gathering data at the critical bwlch of Mynydd Cil Cwm

We now lost height heading toward Bryn y Fedwen, this hill is listed as a Pedwar with 32m of drop based on a basic levelling survey conducted on 16.10.03, and it is also given the same 32m of drop on Ordnance Survey maps with a 373m spot height appearing on the Ordnance Survey enlarged map on the Geograph website.  However, before Trimbling the summit and critical bwlch of Bryn y Fedwen, the next connecting bwlch was that of Moelfre, and this was the next point to survey.

As we made our way down to the critical bwlch of Moelfre the land to our south-west slipped into connecting steams all rising to the eloquent shaped Foel Fadian, which is another Uchaf overlooking carved out plunging northern land.  Further north Moelfre and Llannerch yr Aur gave a foretaste of our continuing route, with the former defaced on its upper southern slopes by felled forestry, whilst the latter was a mass of purple as heather and its association with wilderness predominated.

The elegant profile of Foel Fadian

The purple hillsides of Llannerch yr Aur

The next critical bwlch was situated in a large sheep pen which took up all of the area of the bwlch with its connecting pens and fenced off areas.  As the Trimble gathered its allotted data Aled waited patiently beside a gate and I jotted down the details of the survey, noting the time, number of satellites the Trimble had logged onto, name of hill, the position of the survey – be it a summit or a bwlch, the measurement offset which in this instance was 0.41m as the Trimble had been placed on the top of my rucksack which made a convenient and improvised substitute for a tripod, the feature where the equipment was placed – in this instance gravel / grass in large sheep pen, how many data points gathered which is usually 300, duration of survey which is usually five minutes and lastly the estimated margin of uncertainly associated with the height placement, in this instance I estimated 0.1m.  All of this is scribbled as quickly as possible and sometimes gives little chance to take in and fully appreciate ones surroundings.

The sheep penned critical bwlch of Moelfre with Bryn y Fedwen beyond

Above the sheep pens the greened summit of Bryn y Fedwen stood out and was attractively set against a foreground of bright yellowed gorse.  By now the sun was forever sinking in the western sky and we knew that we would be chasing daylight toward the end of the planned hills and their surveys.  But to be out on the hill when daylight turns to dusk and the sun ebbs its last is a wonderful experience and with my car parked relatively high and a fence to follow down to it from our last hill, we knew that although darkness may overtake us we would be safe for the descent.

The greens and yellows of Bryn y Fedwen

Gathering data at the bwlch of Moelfre

Once the Trimble was packed away we headed up to our next summit which is easily identified, within a couple of minutes the Trimble was set aligned with the high point of Bryn y Fedwen and gathering the customary five minutes of data.  This hill is unusual as it connects two distinct small land masses which have steep steam vallied northern and southern slopes, it seems almost island like, squeezed into its small domain and dominated by its higher neighbours.  This unusual aspect gives it charm and its slopes give easy access to the higher hills to its north and south, and it was the northern land we now continued toward, but our next survey was only a few hundred metres away at the connecting bwlch to Moelfre, which was our next hill.  The connecting bwlch is placed on a gravelled track and we took two data sets from it, one either side of a gate.

Heading toward the summit of Bryn y Fedwen

Aled at the summit of Bryn y Fedwen

Gathering data at the summit of Bryn y Fedwen

Gathering data at the bwlch of Bryn y Fedwen

Our onward route followed a forest track for a short distance before we branched off on a green track as it wound its way steeply up the southern slopes of Moelfre.  This hill dominates this northern part of our route and its summit area is small and flattish, when we arrived I tried to regain my breath and assembled the Trimble as quickly as possible as we still had two hills to visit and quite a distance to cover.

Gathering data at the summit of Moelfre

Up until now the majority of this walk had been on high re-claimed land now given over to sheep grazing with closely cropped grass amongst longer breeze blown grass, with only the summit of Mynydd Cil Cwm still retaining its wild element of heather, but all this was to change as the next hill on our route was shining purple ahead of us with copious amounts of heather on display.  This hill is Llannerch yr Aur and it is another that I had surveyed with my old wooden staff with a 34.7m drop value attained, however the accuracy of this survey is questionable as the territory it was conducted on is not conducive for such things, my surveying notes of the day give the following detail ‘measured from a small puddle at the south-western end of bwlch, this hill is all heather and is another fine little addition’, this sentiment is as applicable today as in October 2003 from the hill first entered the ranks of hills now known as Y Pedwarau.

Llannerch yr Aur - resplendent in its purple haze

As we descended toward the bwlch the heather proved a delight to walk through as it was soft and formed a relatively flat under surface with clouds of dust pollen rising as we continued through it.  What proved bothersome were the grass tussocks which formed next to wetter areas, once at the area of the bwlch a fence marched across it in a south-west to north-east direction, we couldn’t linger as the sun was forever getting lower in the sky and once the land was assessed the Trimble was placed on top of my rucksack and data gathered.  This position proved to be beside the same puddle that I had surveyed from, 12 years ago.

Heading toward Llannerch yr Aur

Gathering data at the critical bwlch of Llannerch yr Aur

By now the day’s exertions were beginning to take their toll and as we made our way up toward the summit of Llannerch yr Aur, Aled went ahead and at every rise he then continued, as I was behind him I hoped that the next rise would prove to be the high point but there were at least three false summits, but as with every hill the true summit is eventually reached.  This particular hill has two distinct possibilities for its high point, before setting the Trimble up we both judged their merits and both decided that the furthest one from the direction that we had approached from, looked the higher. 

As I placed the Trimble on my rucksack at the summit Aled went to the edge of steep ground that looked out to our south and east and he beckoned me to join him, I waited until the file had been created in the Trimble and it was set to achieve its 0.1m accuracy before data should be logged, before venturing down to join him, and the view when I got there was sublime and accentuated by the low light and the purple haze of heather with dulled sun afterglow on distant hills.  I stood and looked at this scene and only interrupted my gaze to press ‘Log’ before re-joining Aled.  The land plunged down below us into gathering shade with the ebbs of the evening sun now just highlighting immediate land and far off hill tops.  We could not linger as we still had at least two surveys to conduct.

Admiring the view

Gathering data at the summit of Llannerch yr Aur

The view south-west from the summit of Llannerch yr Aur

Leaving the summit of Llannerch yr Aur we headed back toward its bwlch and then gained ground whilst contouring north toward a small pool that feeds water into Llynnau Caeconroi, which I had walked past on my only previous visit to these hills.

On our way toward Banc Bron Derwgoed

Dusk was quickly overtaking us as the sun had now dipped behind the intervening hillside, but as we walked down steep ground and over the stream feeding from the high pool and up the other side we came back out into the last remnants of light.  This stream is placed in a rather beautiful place with hillsides of gorse and fern that had dimmed in the evening light adding gentleness to the framed view of our last hill of the day; Banc Bron Derwgoed.

Heather, gorse and fern dimmed in the evening light with Banc Bron Derwgoed beyond

Llynnau Caeconroi

By the time we had gained the track on the ridge that leads down to the bwlch of Banc Bron Derwgoed the sun was aglow in the western sky with its orange orb quickly disappearing from view, we had enough time to take a number of photos before pressing on to the hill’s critical bwlch.  We now knew that dusk and possibly darkness would overtake us so we assessed the lay of land at the critical bwlch and judged where the Trimble should be placed and then continued to the summit.

Daylight quickly disappeared as we approached the bwlch and summit of Banc Bron Derwgoed

As darkness approached we still had four surveys to conduct

Banc Bron Derwgoed is another interesting hill for those who immerse themselves in numerical data as it is listed as a Pedwarau with 30m of drop based on a 30.2m basic levelling survey conducted on the same day as those for Llannerch yr Aur and Bryn y Fedwen, but it is not listed in the Tumps as I suspect that that listing relies upon current Ordnance Survey data for its exclusion.  The Ordnance Survey map data gives a drop value of 28m for this hill based on a 404m summit spot height and a 376m bwlch spot height.

When we got to the summit and started assessing the land we knew it would be dark before we left as there are three distinct possibilities for the high point of this hill, with a fourth point also considered but visually dismissed.  Each of the three points was Trimbled, and very quickly the last ebbs of light that were still with us when we had arrived on the summit were now disappearing and by the time that the third potential summit survey was taking place the whole land had turned dark and only silhouettes of distant hills could be glimpsed.

Gathering data at the first of three surveys conducted at the summit area of Banc Bron Derwgoed

Once the third survey was complete at the area of the summit I packed the Trimble away and we retraced our route back toward an area of intervening gorse, we tackled this from a different approach compared to our ascent, and thankfully this proved easier, beyond this we kept beside the ridge fence which led us back down to the connecting bwlch and the last of fourteen surveys for the day.  Having assessed the bwlch on our ascent we knew where the Trimble should be placed and within a few minutes it was set up gathering data.

Gathering data at the critical bwlch of Banc Bron Derwgoed, the last of fourteen surveys for the day

All that remained was a wander down dark hillsides beside a fence and back to my car.  The walk had taken us 6 hours 25 minutes with much of this time being taken up with the fourteen surveys.  The hills on route are recommended as they are seldom visited and give a perspective to the Pumlumon range lacking from their higher and more popular counterparts.

Survey Result:

Bryn y Fedwen

Summit Height:  404.8m (converted to OSGM15) (Pedwar status confirmed)

Summit Grid Reference:  SN 85170 97211

Bwlch Height:  373.3m (converted to OSGM15)

Bwlch Grid Reference:  SN 85111 97555

Drop:  31.5m (Pedwar status confirmed)

Dominance:  7.79%

Moelfre

Summit Height:  468.1m (converted to OSGM15)

Summit Grid Reference:  SN 84818 98354

Bwlch Height:  362.4m (LIDAR)

Bwlch Grid Reference:  SN 84990 96904 (LIDAR)

Drop:  105.7m (Trimble summit and LIDAR bwlch)

Dominance:  22.58% (Trimble summit and LIDAR bwlch)

Llannerch yr Aur

Summit Height:  437.4m (converted to OSGM15)

Summit Grid Reference:  SN 86309 97855

Bwlch Height:  403.3m (converted to OSGM15)

Bwlch Grid Reference:  SN 85962 98078

Drop:  34.0m (Pedwar status confirmed)

Dominance:  7.78%

Banc Bron Derwgoed

Summit Height:  404.2m (converted to OSGM15)

Summit Grid Reference:  SN 87154 98796 (summit relocation confirmed)

Bwlch Height:  376.4m (converted to OSGM15)

Bwlch Grid Reference:  SN 86863 98871

Drop:  27.7m (Pedwar reclassified to 400m Sub-Pedwar)

Dominance:  6.86%

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