Mapping Mountains – Trimble Surveys – Hirddywel

 

18.10.20  Y Foel (SO 018 840) and Allt y Moch (SO 022 849) 

Y Foel (SO 018 840)

I’d visited Allt y Moch as one of three walks after lock-down restrictions were lifted in early July.  I’d previously surveyed the hill with my old basic levelling staff as having approximately 29.4m of drop; and as the Trimble result came to 29.98m of drop it was time to re-visit and concentrate on the area of the hill’s bwlch and take further readings from its summit. 

When the Trimble result was sent to Aled he suggested we could combine the re-survey with a visit to Y Foel which is positioned across the intervening small stream valley, with each hill visited from the convenience of a relatively high parking place as a there and back walk. 

The day’s forecast was relatively good with dry conditions and little breeze, and although the day proved to have grey skies the cloud base was above the tops.  We met in Caersŵs and I drove the remaining distance to the hill and parked on a grass verge beside the track that leads down to the old farm house of Foel-Fawr. 

Heading toward Y Foel

Y Foel is a great lump of a forested hill which if not for the conifers would no doubt give excellent views.  Reaching the old farm house which is now no more than a ruin we headed on the continuation of the track in to the conifers.  From the track there are a number of options to head up on forest breaks toward a narrow path that follows this hill’s north-westerly ridge all the way to the summit.  This is the route that Charlie Leventon and I used on my only previous ascent in September 2011. 

We followed one of the rides steeply up to a forest break and after a quick investigation found the ridge path.  This simplified matters as all we now had to do was follow it up until the summit was reached. 

The forest break leading toward the ridge path

Walking on a path through a forest can have its own beauty, in some ways this is similar to walking in mist as few views can be seen and one’s world is suddenly condensed to the immediate surrounds.  It was no different today and as height was gained we started to look out for the small cairn beside the path that constitutes the summit position. 

The ridge path leading toward the summit

We reached what we thought was the summit, but could not see the cairn, therefore we continued in the same direction to make sure that all ground now went downhill, it did, so we headed back to the high part of the hill.  We chose a spot for Trimble placement and before setting it up to gather data I used it as a hand-held device and headed in to the trees to find the spot that LIDAR gives for the summit.  The LIDAR placement was about 15 metres in to the conifers and after assessing the ground I headed back to our preferred high point. 

As I took the measurement offset between the internal antenna and the ground at the base the bottom of the tape hit rock.  This proved to be the small cairn which is now covered in moss and hardly recognisable from what it looked like nine years ago. 

Gathering data at the summit of Y Foel

Prior to setting the Trimble up we headed through one or two conifers to the steep southern flank of the hill which is clear of trees, and sat looking out across the Nant Glyn and beyond to higher hills.  Once back in the trees I set the Trimble to gather data. 

Out of the conifers, the view across the Nant Glyn

Once the allotted data were gathered and stored were reversed our inward route and headed back to where my car was parked, here we met the couple who live at Borth; the small holding just down the narrow lane.  One was sitting on a horse and the other on a quad bike and with their dog happily following they were out for the day.  We chatted for a number of minutes before they headed up the lane. 

Allt yr Moch (SO 022 849)

We now wanted to visit Allt y Moch and followed a green track on the hill’s southern flank which led to the gate at the bwlch.  We knew from the data sets taken on my previous visit where the area of the bwlch is positioned.  However, this is not difficult to ascertain just by eye. 

I’d brought flags in case these were needed and we spent a few minutes deciding how many data sets were to be taken and from where.  Having assessed the lay of land we opted for four data sets, all relatively close together and concentrating on land just to the north of the fence that crosses the bwlch on a hill to hill direction. 

Whilst waiting for the Trimble to achieve its 0.1m accuracy level before data should be logged the conditions progressively got colder, as by now a slight breeze had descended across the bwlch.  However, we persevered and eventually left the bwlch having taken the four data sets that we wanted. 

Gathering data at the bwlch of Allt y Moch

A greened vehicle track leads from the bwlch toward the summit of Allt y Moch and we followed this up to its high point.  On my last visit I’d taken four data sets from the area of the summit with three of these concentrating on its higher ground, and once we had assessed the lay of land and positioned a number of flags, each inserted in the ground to the same level, the flags were then Abneyed and we removed those that were lower, leaving two remaining. 

Gathering data at the summit of Allt y Moch

During data collection we sat on the northern side of the hill out of the breeze and enjoyed the view.  Once the second data set was gathered and stored, I closed the equipment down, packed it away and we headed down following our inward route back to the awaiting car.   

 

Survey Result: 

 

Y Foel  

Summit Height:  435.8m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SO 01864 84066 (Trimble GeoXH 6000)

Bwlch Height:  319m (spot height)

Bwlch Grid Reference:  SO 02299 84267 (spot height)

Drop:  117m (Trimble GeoXH 6000 summit and spot height bwlch)

Dominance:  26.81% (Trimble GeoXH 6000 summit and spot height bwlch)

 

 

Allt y Moch  

Summit Height:  419.7m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Summit Grid Reference:  SO 02202 84938 (from previous Trimble GeoXH 6000 survey)

Bwlch Height:  389.6m (converted to OSGM15)

Bwlch Grid Reference:  SO 02366 84827

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

Dominance:  7.17%

 

 

For details on the first Trimble GeoXH 6000 survey of this hill

For further details please consult the Trimble Survey Spreadsheet