Mapping Mountains – Trimble Surveys – Hirddywel

02.02.18  Llain (SO 031 628), Rhiw Gwraidd (SO 016 634) and Dôl y Fan Hill (SO 015 611)

Dôl y Fan Hill (SO 015 611)

In June 2010 I spent a long time on the summit ridge of Rhiw Gwraidd line surveying it with John Barnard and Graham Jackson; we pinpointed the summit of the hill but did not take a data set with the Leica equipment to establish its height.  Ever since getting the Trimble GeoXH 6000 I’ve wanted to re-visit and gather data from its high point to finally give this hill an accurate summit height.

I set off from the small community of Llanllŷr to the north-west of Llandrindod at just before 9.15am, and with daylight hours now edging past 5.00pm and with a forecast of light breeze and in the main dry conditions, albeit a little chilly, I was in no rush.

A narrow lane headed up toward Fron-serth, I planned on calling, hoping that it was still a farm, it wasn’t, but the man who had moved there with his wife a number of months ago was extremely helpful and walked down the track with me to show where the ladder style was placed and the continuation of the path toward my first summit of the day.

The approach to Llain

Llain is given 19m of drop on Ordnance Survey maps with a 361m summit and 342m bwlch height, therefore it was close to being a Sub-Trichant, this was the only excuse I needed to survey it, this and that by doing so it would form a part of a good circular walk taking in the higher summits of Rhiw Gwraidd and Dôl y Fan Hill.

The view west from the summit of Llain

Although these hills are in the main now grazing pasture, there is a peaceful solitude to wandering such places at this time of year, seldom do you encounter any one, and the land seems to merge, almost sleep, and yet still be alive, it is a sensation that I’ve experienced on many an occasion and yet it still fills me with pleasing and an inner contented happiness.

I took two data sets from the summit area of Llain, with the first my preferred high point; both were good little summits with expansive views.  Whilst the Trimble gathered its allotted five minutes of data from each point I studied the map for which fence to follow down toward this hill’s connecting bwlch and then on to the higher summit of Rhiw Gwraidd.

The first and higher data set taken at the summit of Llain

The second and lower data set taken on Llain

The bwlch proved to be beside a drainage ditch with a small earthen embankment no doubt put in place when the ditch was excavated, I set the Trimble up where I judged the critical bwlch to lie and waited in the morning’s sunshine as it collected another data set.

Gathering data at the bwlch of Llain

Leaving the bwlch I watched two Red Kites majestically circle and glide as their red golden colour flashed against catching sunlight, it was good to be out on the hill even if the fields today were sodden and particularly mud splattered in places.

Beyond the bwlch a footpath led up steepening fields to a number of foot styles and gates giving access toward the track that heads to the large mast perched on one of the number of bumps atop Rhiw Gwraidd.  As I crested the ridge a chilled slight breeze blew and ominous shower clouds had sprung up in adjoining valley’s, their slate grey contrasting against the illuminated light blues and white clouds that otherwise heralded a good dry day.

It wasn’t far beyond the large mast to the high point which is marked by a small embedded rock about one metre from a small cairn.  Before setting the Trimble up aligned to the highest part of the small rock I looked at it and memories of the line survey flooded back, we spent a number of hours on this ridge having a good time and producing an excellent set of results from the line survey, I still feel sad when I think of these times as we operated extremely well as a team both on and off the hill, but life moves on and sometimes events dictate that such times can unfortunately no longer take place.

As the Trimble gathered data the sky menaced from above with shower clouds pushing westward, these glistened on adjacent hillsides covering them wet; I stood and waited for the deluge but thankfully only a few spots lingered my way.

Gathering data at the summit of Rhiw Gwraidd

Packing the Trimble away is always a good moment as it means another data set to process and another accurate result obtained, it also means progress toward the next planned hill and for me this was through a gate and down steeply on ever increasing wet and muddy grass toward the muddied yard of Upper Cilgee.  I stopped and chatted briefly with the farmer’s son and a number of contractors’ before moving on up the lane, by now raindrops were falling pinpointing little echoed waves in brown puddles, my back was to the few drops that fell and it was only these blemishes in near puddles that showed me that the intensity of rain was greater than I imagined.  Leaving the lane for a track hail then started to fall, this only lasted a few minutes and was surprisingly welcome, it brought a different feel to the air, one that chilled, but again it was only fleeting and slowly the blue cascaded down again after the sun appeared.

Dôl y Fan Hill (SO 015 611)

My next survey was the bwlch for Dôl y Fan Hill, this proved to be hard to judge and was somewhere in a large green grazing field, when I arrived there I wandered back and forth and kept trying to follow the undulations toward where the critical bwlch was placed.  I eventually decided on my spot and gathered a five minutes data set, during which a huge shower threatened from the west as it rolled down the valley engulfing the near hills and turning everything wet.  Only a few drops sped my way, I was literally just on the edge of the grey mass of rain and certainly didn’t want to walk toward it, the last I saw of it was as it wandered southward toward Mynydd Epynt throwing out rain drops resembling silvered cascades.

Hail showers massing

Gathering data at the bwlch of Dôl y Fan Hill

Only one survey remained and that was the summit of Dôl y Fan Hill, I used gated fields to gain height to its north-eastward ridge, this proved a delight with ever expansive views and dramatic colour back over Rhiw Gwraidd as another large shower brimmed.

Rhiw Gwraidd with more sleet showers massing

The trig pillar marked the summit and I set the Trimble up aligned with a rock which sat squat beside it.  Whilst gathering data the light was sublime with deep greys and blues above and illuminated colour below, I happily waited for ten minutes of data to be gathered and then stored and just stood and looked and soaked in the view.

The trig pillar at the summit of Dôl y Fan Hill

Colour bounced across the hill, this often happens when low sun and deep grey sky are combined; the colour intensity is often vivid giving an unreal quality to an otherwise pastoral scene.  Such times are to be savoured, the hills give many such moments, but still, one never knows when the next will occur. 

The view northward from the summit of Dôl y Fan Hill

Once the ten minutes were up I pressed ‘Done’ and took a number of photographs before closing the Trimble down and packing it away, all that remained was to follow the north-easterly ridge down to where a track gave access to a field and the continuation of the track contoured around gaining height occasionally leading to the top of a minor lane that took me back to Llanllŷr. 

Gathering data at the summit of Dôl y Fan Hill

LIDAR image of Dôl y Fan Hill (SO 015 611)

LIDAR image of Llain (SO 031 628)

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.  Subsequently these hills have been analysed via LIDAR and it is this result that is being prioritised in preference to that produced by the Trimble GeoXH 6000 survey for the bwlch of Dôl y Fan Hill and Llain.

Survey Result:

Llain (significant name change)

Summit Height:  360.6m (converted to OSGM15) (Trimble GeoXH 6000)

Summit Grid Reference:  SO 03132 62802 (Trimble GeoXH 6000)

Bwlch Height:  341.3m (LIDAR)

Bwlch Grid Reference:  SO 02799 62931 (LIDAR)

Drop:  19.4m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Dominance:  5.37% (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Rhiw Gwraidd

Summit Height:  441.7m (converted to OSGM15) (Trimble GeoXH 6000)

Summit Grid Reference:  SO 01606 63432 (Trimble GeoXH 6000) (summit relocation confirmed)

Bwlch Height:  229.6m (LIDAR)

Bwlch Grid Reference:  SO 00810 64998 (LIDAR)

Drop:  212.1m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  48.02% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dôl y Fan Hill

Summit Height:  379.9m (converted to OSGM15) (Trimble GeoXH 6000)

Summit Grid Reference:  SO 01536 61170 (Trimble GeoXH 6000)

Bwlch Height:  309.2m (LIDAR)

Bwlch Grid Reference:  SO 02069 61849 (LIDAR)

Drop:  70.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  18.63% (Trimble GeoXH 6000 summit and LIDAR bwlch)

For further details please consult the Trimble Survey Spreadsheet