Mapping Mountains – Trimble Surveys – Drygarn Fawr

16.09.23  Mynydd Trawsnant (SN 824 485) 

The summit area of Mynydd Trawsnant (SN 824 485)

Mynydd Trawsnant appears in a number of hill lists, including the Welsh Highlands – Uchafion Cymru, the Deweys and the 500m Twmpau.  Its summit position in these lists has recently been relocated due to LIDAR analysis conducted by Aled Williams. 

LIDAR summit image of Mynydd Trawsnant

Mynydd Trawsnant is one of many hills is this area that have been swamped by conifer plantation which forms a part of the extensive Tywi Forest.  However, recent visits to its relocated summit reported the forestry in this section felled with newly planted trees already in situ.  Because of this it was an ideal time to visit and gather Trimble data to compare to that of LIDAR.

I had visited its previously listed summit position once before when the barrier at the start of the forest track leading toward its summit was open, not wanting to pass on this invitation I drove up the track and parked close to its then recognised high point.  Before visiting the summit I heard the approaching sound of a forestry lorry and therefore quickly hid behind a tree.  Logging was in progress and not wanting to linger I quickly scampered up the forest ride to what was then considered its high point and just as quickly scampered back down before driving down the forest track to the minor paved road at its end.

Today, along with Aled, we wanted to gather data from the LIDAR high point.  Ideally another data set should be gathered from the old summit position, but again recent visits indicated this was still submerged in conifers.

It’s a long drive south close the eastern shore of Llyn Brianne to where the forest track heads up toward the summit of Mynydd Trawsnant.  Approaching the track we saw that the barrier was open giving access up the hill.  Driving toward the hill we had seen a number of notices relating to a race that was taking place and the arrows indicating the way ahead for the runners pointed up the same track, we wondered whether the barrier was open to give access to the runners and any support vehicles following the race. 

Parked and ready to tackle the relocated summit of Mynydd Trawsnant

Having driven up the track we parked as close to the summit as we could and set off walking at 8.55am as the first flecks of forecast rain began to push northward.  This would herald damp and misty conditions for the continuation of the walk Aled had planned.  However, for me I only had one summit to visit and this was ever so close to where we had parked. 

Setting off up the forest ride between the mature conifers and old summit position on the left and the felled forestry and new summit position on the right

A forest ride between the felled section and the remaining mature tees gave good access and relatively easy underfoot conditions over and close to the old summit position toward the slightly higher LIDAR summit which was ahead of us and to our right.  This as with many felled forested ground looked like an assault course, but thankfully none of it was difficult, although I did manage to almost sit in a water course as I slipped and fell. 

Typical felled forestry land made even more bleak by the grey overhead conditions and incoming rain

The Trimble was used as a hand-help GPS unit to zero in to the co-ordinates ascertained from LIDAR analysis.  When there we debated where the survey equipment should be set up and opted to align it with a patch of grass that was solid and stable.  As the Trimble collected data I sat on a tree stump and scribbled all necessary detail in my survey note book. 

Gathering data at the summit area of Mynydd Trawsnant

Once the equipment was packed away we reversed our inward route, but this time avoiding the water course and aiming for the corner of forest as it butts up against the open hill to its north.  This gave a semblance of what these hills were like before the infestation of conifers.  The open hillside was expansive, albeit with the customary thick and rough Elenydd summer grassland in evidence. 

Heading back to the forest track

Once back at the car I waved Aled off, who was continuing south wanting to visit two subs in the forest before breaking out of the conifers to visit Garn Wen, which is listed as a Dewey and lastly a Pedwar overlooking Llanwrtyd, where we had arranged for me to pick him up in the early afternoon. 

Aled heading off farther in to the forest for what proved a wet and misty few hours

I then set off driving back down the forest track, stopping once to speak with a man who was standing outside his vehicle setting up a small food and drink station for the runners in the race.  He told me there were 21 runners, although the number was originally higher with a number having recently pulled out.

Once out of the forest and back on the minor paved road close to Llyn Brianne I stopped and changed as the rain fell.  It looked a particularly murky scene with grey predominating with mist enclosing many near summits.  It took 55 minutes to drive from here to Llanwrtyd, stopping once to chat with a farmer.

Once at Llanwrtyd I found the car park we had arranged to meet at, read a book, sheltered from the rain and once this stopped walked in to town to find that Caffi Sosban served an all-day breakfast, which once Aled had completed his walk we visited and ate.  An excellent way to end a walk!      

 

Survey Result:

 

Mynydd Trawsnant                   

Summit Height:  516.6m (LIDAR)

Summit Grid Reference:  SN 82452 48564 (LIDAR) (summit relocation –Deweys) (summit relocation – 500m Twmpau and Welsh Highlands – Uchafion Cymru)

Bwlch Height:  378.3m (LIDAR)

Bwlch Grid Reference:  SN 82781 50423 (LIDAR)

Drop:  138.3m (LIDAR)

Dominance:  26.77% (LIDAR)

 

 

For further details please consult the Trimble Survey Spreadsheet