Saturday, 20 August 2016

Mapping Mountains – Trimble Surveys – Cymoedd


23.07.16  Pt. 523m (SS 928 951)    

Pt. 523m (SS 928 951)

This hill is positioned beside the A 4107 as it makes its way from the junction with the A 4061 above Hirwaun, westward toward the confines of Abergwynfi and Cwm Afan.  Because of this it is no more than a few minutes stroll to its grassed top.  It is rather forgotten, as many hills are that have higher and more prominent neighbours, but according to a basic levelling survey conducted in August 2005 it is close to meeting the requirements for Uchaf qualification, these are the Welsh hills at or over 500m in height that have a minimum of 15m of drop, and is a list that Aled and I plan on publishing in the future.

Toward the end of the time that I was wandering the Welsh hills surveying for drop with my rudimentary staff I was also making place-name enquiries, and this hill has a locally known name, however the point (Pt. 523m) notation is currently being used for this hill as its locally known name will be given when the list known tentatively as Yr Uchafion is published.

The bwlch connecting this hill to its higher neighbour is positioned north-westward of its summit and the A 4107 runs across it in roughly a hill to hill direction.  The road is elevated above its surrounding land with prominent ditches below and earthen embankments on either side.  When I first surveyed this hill I noted the roads elevation and the ditches below it and measured from the low point of the road to the summit of the hill.  Eleven years later and I now wanted to take a series of readings from the area of the bwlch.

The elevated road passing over the area of the bwlch

I parked just off the road where a motorcycle track veers up to the hill and proceeded to walk the short distance down the road and on to the natural ground to its south.  Immediately I dropped down in to the ditch and then walked up the other side on to what can be viewed as a part of the remaining natural ground of the hill.  I took one data set from where I judged the low point of this ground on the hill to hill traverse to be situated and then headed back to the road.

The Trimble set-up position on the south side of the road

Above the road on either side of it is also an embankment, I stood on top on this on its southern side and assessed the road for its low point as I wanted to take a data set from this point to compare its elevation to the remaining natural ground on its northern and southern sides.  The assessment of the roads low point was made easier by the placement of two manhole covers directly opposite one another, these are good indicators where water run off goes and are usually placed at the low point of a road.

The next data set was taken at what I judged to be the low point of the hill to hill traverse on the ground to the north of the road, it is this position that I think to be the point where the natural critical bwlch still exists as cotton grass and a small bog laden grassy channel crept upward to the luxuriant greened summer grasslands of the bwlch.  Once another five minute data set had been gathered I packed the equipment away and headed up to the hill’s summit.

The Trimble set-up position on the north side of the road

The summit area has two tops with the further westerly one the higher, I placed the Trimble on top of my rucksack to give it elevation above the long grass, measured a 0.42m offset between the equipment’s internal antenna and the ground at the base of the rucksack and set it to collect data.  All that remained was to take a data set from the low point of the road.

Gathering data at the summit of Pt. 523m

As I headed down the hill to where my car was parked a westerly cloud bank edged ever eastward, this heralded rain which was predicted in this part of the country by late afternoon.  I moved my car down the road and positioned it next to the manhole cover signifying where I judged the low point of the road to be situated and positioned the Trimble on top of the car’s roof, measured a 1.44m offset and set the equipment to gather the last of the day’s five minute data sets.

The afternoon's blue sky and beautiful high cloud was about to be replaced by a westerly cloud front

The last data set of the day atop my car at the low point of the road

Once five minutes of data were gathered I packed the Trimble away, drove to a lay-by, changed and sorted my gear and headed down to the M4 for my onward journey to St David’s and tomorrow’s island adventure organised by Adrian Rayner.



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