Mapping Mountains – Trimble Surveys – Cadair Idris

17.02.18  Ffridd Nant y Gwyrddail (SH 674 147, only bwlch surveyed)

The bwlch of Ffridd Nant y Gwyrddail (bwlch at SH 662 134)

Having visited three hills close to where the critical bwlch of this hill lies I thought I should at least visit its boggy depths and obtain data, as this can be compared against the data that was gathered using a Leica GS15 when along with John Barnard and Graham Jackson we investigated this spot whilst surveying for the position of the critical bwlch of Pared y Cefn Hir (summit at SH 661 148).

It seems a long time ago when in November 2012 this bwlch was surveyed using the Leica equipment, as we had surveyed the summit of Pared y Cefn Hir and its adjacent hill of Bryn Brith, we needed to find the position of the bwlch connecting the higher of these two twin topped 383m map heighted hills to ascertain its drop value, and as the map indicated three positional possibilities for this critical bwlch, each in turn needed surveying, and the bog that makes up this potential bwlch position was by far the most soggy and unwelcome, to the point that after standing immersed in the bog operating the staff for about 45 minutes I thought I was suffering from trench foot!

Using level and staff in November 2012 to determine the bwlch position of Ffridd Nant y Gwyrddail

Today was an easy proposition in comparison as I had come prepared with the ten figure grid reference for this bwlch position.  When surveyed with the Leica GS15 this position proved not to be the critical bwlch of Pared y Cefn Hir (which proved by 0.09m to be the higher when compared to Bryn Brith), but it is still a connecting bwlch for another hill, and that hill is positioned down stream of this bwlch to its north-east with its summit given a map height of 312m at SH 674 147, the hill remains unnamed on the map but a visit to a local farmer after this survey gave the name of Ffridd Nant y Gwyrddail for the bounded land where the summit of this hill is situated.

It was only a couple of minutes’ drive from where my car was parked to where a passing place beside the minor road gave me an opportunity to leave the car for the short period of time this bwlch survey would take.

I was soon in the bog, thankfully wearing wellies this time, and used the Trimble as a hand-held device to zero in on the ten figure grid reference.  Even after doing this the underfoot conditions would still give a large margin of uncertainty to Trimble placement as tussock grass predominated. 

Gathering data at the critical bwlch of Ffridd Nant y Gwyrddail

As the Trimble ebbed down to the 0.1m accuracy level before data should be logged I watched as the delicate play of light slowly cast down upon adjacent hills, with the coned and pyramidal profile of Ffridd Bellau Nant y Gwyrddail looking particularly fine. 

Ffridd Bellau Nant y Gwyrddail (SH 665 139) on the left and Ffridd Nant y Gwyrddail (SH 674 147) on the right

Once the 0.1m accuracy level appeared I pressed ‘Log’ and waited for the allotted five minutes of data to be gathered.  My stay in the bog had been a short one, and especially so when compared to my last visit.  Once back at the car I drove the short distance down the valley and called at Nant-y-gwyrddail before visiting Emyr Rees of Tynyceunant.

Survey Result: 

Ffridd Nant y Gwyrddail (significant name change)

Summit Height:  311.5m (LIDAR)

Summit Grid Reference:  SH 67419 14719 (LIDAR)

Bwlch Height:  237.7m (converted to OSGM15, Trimble GeoXH 6000)  237.7m (converted to OSGM15, Leica GS15)

Bwlch Grid Reference:  SH 66210 13444 (Trimble GeoXH 6000 & Leica GS15)

Drop:  73.8m (LIDAR summit and Leica GS15 & Trimble GeoXH 6000 bwlch)

Dominance:  23.69% (LIDAR summit and Leica GS15 & Trimble GeoXH 6000 bwlch)

For further details please consult the Trimble Survey Spreadsheet