Monday, 19 October 2020

Mapping Mountains – Trimble Surveys – Hirddywel


11.07.20  Allt y Moch (SO 022 849)  

Allt y Moch (SO 022 849)

In August 2003 I set out with good intention to reach the forested summit of Y Foel (SO 018 840).  After about 45 minutes I emerged out of the trees having had one of those adventures when you’re not sure where you’ve been or where you now are.  I salvaged the day by heading across the intervening valley and finding a forestry track that led me toward Allt y Moch.  I proceeded to survey this hill with my old basic levelling staff and concluded that it had approximately 29.4m of drop.  This method of surveying is only basic, but was responsible for a number of hill reclassifications.  Considering its method many results are accurate, however some aren’t, and this could be one of them as the latest online mapping suggests this hill to be a P30 and therefore I wanted to revisit and survey it with the Trimble GeoXH 6000.

Access to the hill is easy as there’s one or two places to park at the end of a narrow paved road that makes its way uphill toward one of the many access tracks that lead into the western part of the Pegwn Mawr range.  From here it was a short walk on the continuation of the track before taking a branch off on the left that led straight to this hill’s bwlch.

The track leading to the bwlch

I remembered from my last visit that the bwlch had some sort of construction on it, this proved to be a high sided large sheep fold.  Thankfully it wasn’t positioned over the critical point.  I spent an inordinate amount of time at this bwlch as it took seven attempts before the Trimble complied with my wishes and reached its 0.1m accuracy level before data should be logged.  At one point I removed its battery and then re-booted it.  Why this happened I do not know, but wonder if five months inactivity had made it sluggish, a little like its owner, perhaps.

During the first bwlch survey I decided to take at least one more data set on the valley to valley traverse, and during this second survey I decided a third was needed.  This would give a good spread of results and show the lay of land over a 20 metre or so distance.

Gathering data at the bwlch of Allt y Moch

A greened track led up from the bwlch toward the summit, it was so good to be in such a place, it wasn’t dramatic, but it was a hill and I’d missed their openness over the last four months during the enforced and necessary lock down.

Once at the summit I proceeded to take four further data sets, three from near to where the 421m spot height appears on the Ordnance Survey 1:25,000 Explorer map and one from where the summit ridge continues north-westward.  During each data set I stood below the Trimble and looked out to the west across miles of cultivated, forested and in patches wild land toward the higher hills of the Aran and Berwyn.

Gathering data at the summit of Allt y Moch

Packing the Trimble away I retraced my route back to the connecting bwlch and headed down beside a fence line which took me to within a few metres of where I’d parked my car.  Allt y Moch would be a fine addition to the Y Pedwarau, we’ll just have to wait for the data to be processed until its status is hopefully confirmed.


Survey Result:


Allt y Moch
  
Summit Height:  419.7m (converted to OSGM15)

Summit Grid Reference:  SO 02202 84938

Bwlch Height:  389.6m (converted to OSGM15, from subsequent Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SO 02366 84827 (from subsequent Trimble GeoXH 6000 survey)

Drop:  30.1m (400m Sub-Pedwar reclassified to Pedwar)

Dominance:  7.17%









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