Mapping Mountains – Trimble Surveys – Pumlumon

02.05.14  Y Gaer (SO 013 873) and Gelli Hir (SN 999 883)

This is the second of two Trimble surveys of Y Gaer and Gelli Hir, to read the first survey post please click {here}

Gelli Hir (SN 999 883)

These two 308m map heighted hills were Trimbled on the 07.02.14, resulting in a height difference of 0.06m, with Gelli Hir being the higher.  As a 6cm difference is within the margin of uncertainty associated with the equipment the two hill's were prioritised for a Leica GS15 survey.  Currently Mark Jackson has them listed as a twin Hump under the names of Coed Mawr and Rhos Fawr, with Coed Mawr being given priority Hump status and Rhos Fawr listed as the Subhump.

By 9.00am my car had been loaded with all necessary surveying equipment transferred from John's car and along with Graham we made our way toward Llandinam and the minor road between the two hills that follows the Nant yr Hebog.  We scouted around for a suitable parking space and eventually asked permission to park next to a bungalow close to the critical bwlch between the two hills, permission was kindly given, and by 9.50am we were on our way, following the Severn Way up a track and over fields to the northern ridge of Y Gaer and then on to the summit.

There was dullness to the day with high blanketed cloud cover giving a monochrome effect to the land.  The forecast was good with mid Wales predicted to be free of any rain and only a light breeze, which would help as we planned on gathering two hours of data from each hill.

Soon the level and staff was assembled as John looked through the optics and Graham operated the staff.  The summit area of Y Gaer consists of small plateaux like 4m x 4m blob of close cropped grass amongst a greater blob of closely cropped greenery in a sheep grazing field.  Measurements around the summit were within 2cm – 3cm of each other, we soon pinpointed our chosen spot, marked it with a metal stud and put three flags next to it.

As the small summit ridge has a line of trees next to it we levelled away from the high point to where the Leica GS15 set up position was going to be, this was far enough away from the tree coverage not to disrupt satellite signal reception.  Once assembled and switched on we waited for the arrival of Eryl; a good travelling companion and hill walking friend of many a year who planned on joining us for an hour.

Yummy, yummy - quite like the taste of these flags

Stop eating the flags!

Levelling for summit position on Y Gaer

About half an hour later we spotted Eryl making his way up the last section of the northern ridge to join us on the summit; handshakes and hugs proceeded.  I believe the only time Eryl had met John and Graham was on the wake for a deleted Nuttall on the Berwyn ridge, a particularly wet day and an eventful one as we lost Ed for an hour in a lonely mist driven windy land of heather.  He eventually emerged looking rather wild eyed and slightly disheveled.

L-R; Eryl, John and Graham at the Leica GS15 set up position on Y Gaer

Good to see Eryl again, he’d been birding his way up the hill and as John and Graham have a common interest in all things tweety and feathery the conversation flowed.  An hour or so later and he was on his way back down the ridge. 

Once the allotted two hours of data had been gathered with the Leica GS15 and ten minutes of data with the Trimble GeoXH 6000 we packed up the equipment and headed down the southerly ridge to the farm of Cefn (SO 006 868) where I’d met Graham Pugh on my previous visit.  From Cefn we followed a footpath down a green lane to the bwlch between the hills, past the car next to the bungalow and up to the summit of Gelli Hir.

The footpath from Cefn toward the bwlch between the two hills

The summit area of Gelli Hir is similar to that of Y Gaer as it consists of a 4m x 4m green blob of closely cropped grass.  Once we had levelled the area and found the high point we inserted what is now becoming a customary addition to our surveys; a metal stud that John had bought, this is ideal for soft ground as it creates a point for the spike of the two metre pole to be positioned without the possibility of it slowly sinking a few millimetres in to the ground under the weight of the surveying equipment that is screwed to the top of the pole.

Levelling for summit position on Gelli Hir

Graham and John beside the Leica GS15 at the summit of Gelli Hir

The two hours on the summit of Y Gaer had been slightly chilly so we wrapped up and waited for another two hours of summit data to be collected with the Leica and ten minutes with the Trimble and passed the time with good conversation.  Once sufficient data was stored we packed everything away and made our way back down to the car.  A long day on the hill but good to be out with John and Graham again and to see Eryl for an hour.

LIDAR image of Gelli Hir (SN 999 883)

The Trimble GeoXH 6000 gathering data at the summit of Gelli Hir with Y Gaer in centre background

Survey Result:

Y Gaer (significant name change)

Summit Height:  307.1m (converted to OSGM15, Trimble GeoXH 6000)  307.1m (converted to OSGM15, Leica GS15)

Summit Grid Reference:  SO 01350 87380

Bwlch Height:  215.8m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SO 00054 87410 (from previous Trimble GeoXH 6000 survey)

Drop:  91.3m  (de-twinning with prioritised Hump reclassified to Subhump)

Dominance:  29.74% (Lesser Dominant deletion confirmed)

Gelli Hir (significant name change)

Summit Height:  307.2m (converted to OSGM15, Trimble GeoXH 6000)  307.2m (converted to OSGM15, Leica GS15)

Summit Grid Reference:  SN 99903 88383

Bwlch Height:  182.5m (LIDAR)

Bwlch Grid Reference:  SN 97223 88327 (LIDAR)

Drop:  124.7m  (de-twinning with prioritised Subhump reclassified to Hump)

Dominance:  40.60% (Lesser Dominant addition confirmed)

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