Wednesday 27 November 2019

Mapping Mountains – Trimble Surveys – Pumlumon


13.09.19  Bryn Amlwg (SN 921 973), only bwlch surveyed

Beyond the gate is the bwlch of Bryn Amlwg

Bryn Amlwg is a great bulk of a hill whose summit now has wind turbines scattered across it.  These are a part of the Carno wind farm which was first installed in 1996 with 56 wind turbines.  The Carno II project extended the number to 68 with the new turbines reaching a tip height of 80m.

I’d visited the summit of Bryn Amlwg on one previous occasion, in October 2013.  I found the approach from the east to be attractive, and although the vast upland area of this hill still gives distant views any semblance of tranquillity it once had is now replaced by the hummed thud of turbine blades.

The trig pillar and wind turbines at the summit of Bryn Amlwg

Bryn Amlwg is a relatively prominent hill, and as such is listed as a Marilyn and Lesser Dominant.  Today it was its connecting bwlch and not its summit that I wanted to survey.  This point had already been LIDARed by Aled Williams, but as I had enjoyed a morning of breakfast at Suzanne’s, a visit to Lisa’s and catch up with Eryl and Rita in Llanidloes; this hill’s bwlch was just a few miles away and would form the first of six such surveys during the remainder of the day.

The bwlch of Bryn Amlwg is placed to the south-west of its summit in a closely cropped field next to a minor road and beside the drive that leads to a house named Hirnant.  Having knocked on the front door and received no reply I drove back down the drive and parked beside the minor road.  As I stepped out of my car a post van drew up, I explained what I wanted to do and the postman said that the field probably wasn’t a part of Hirnant’s land and that he was sure nobody would mind me wandering around in it for a few minutes.

The gate giving access to the field was only a few metres from where I had parked my car and I was soon walking on the cropped grass beside the mature boundary hedge which kept the minor road at bay.

The land gently ebbed upward to where the critical point lay; it then gently ebbed downward in a more confident fashion.  The point where each met was relatively easy to pinpoint and having the ten figure grid reference produced by Aled’s LIDAR analysis zeroed me in toward the critical point.

Once the Trimble was positioned atop my rucksack and the measurement offset between its internal antenna and the ground below was noted, I set it to gather data and stood back in the early afternoon sunshine.

Gathering data at the bwlch of Bryn Amlwg

The Trimble GeoXH 6000 set-up position at the bwlch of Bryn Amlwg

Five minutes data collection soon passes, and today I stood and looked out on a vividly greened and manicured field that blazed its way in to the almost iridescent blue above.  Both colours screamed out in unison.

Once data were gathered and stored I packed the Trimble away, turned and retraced my way back to the access gate, not a thing had stirred at Hirnant.  My next bwlch survey was only a short drive on the minor road and connects to the Pedwar of Pen y Waun Fawr (SN 878 949).  



Survey Result:


Bryn Amlwg

Summit Height:  488m (spot height)

Summit Grid Reference:  SO 92161 97346 (hand-held GPS via DoBIH)

Bwlch Height:  318.7m (converted to OSGM15)

Bwlch Grid Reference:  SO 87945 93874

Drop:  169m

Dominance:  34.68%

  






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