Mapping Mountains – Trimble Surveys – Pumlumon

11.07.20  Mynydd Derw Llwydion (SN 904 900)  

Mynydd Derw Llwydion (SN 904 900)

This hill is positioned close to Llyn Clewedog and the various pull-ins and picnic tables overlooking the lake were busting with life as I drove around it, it seemed the lifting of the 5-mile keep local restriction had encouraged many people to get out and especially so with the weekends weather forecast giving dry and sunny conditions throughout Wales.  I headed away from the picnickers and parked at the start of the track leading toward the single wind turbine atop this hill.

The track leading to the summit

It was 1.15pm as I parked my car and headed off with all necessary equipment up the track toward the single wind turbine on the summit of Mynydd Derw Llwydion.  I’d been this way before in April 2014 when on a walk from Llyn Clewedog to Staylittle visiting and surveying a number of hills on the way.  The point I’d surveyed for this hill’s summit is where the 387m spot height appears on the Ordnance Survey 1:25,000 Explorer map. 

The survey of this hill’s summit and bwlch resulted in it being promoted to P30 status.  However, since those days LIDAR is now available and this shows the summit of this hill is close to the single wind turbine and not where the spot height is positioned, so a re-visit was necessary.

LIDAR summit image of Mynydd Derw Llwydion

It was only a five minute stroll to the summit and by the time I arrived on the high pint a welcome breeze blew across the land.  After assessing the summit area I chose the spot for Trimble placement and once the 0.1m accuracy level was attained I pressed ‘Log’ and scampered off to wait for the allotted five minutes of data to be gathered and stored.

Gathering data at the summit of Mynydd Derw Llwydion

Reversing my inward route I was soon back at my car, changed and away toward Llanidloes and a socially distanced visit to see Eryl and Rita for a couple of hours catch up sitting in the sun, a fine way to spend an afternoon.

Survey Result:

Mynydd Derw Llwydion  

Summit Height:  389.3m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SN 90460 90041 (summit relocation confirmed)

Bwlch Height:  358.1m (converted to OSGM15) (from previous Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SN 90391 90264 (from previous Trimble GeoXH 6000 survey)

Drop:  31.3m (Sub-Trichant reclassified to Trichant)

Dominance:  8.03%

For details on the Trimble GeoXH 6000 survey of this hill’s bwlch

For further details please consult the Trimble Survey Spreadsheet