Mapping Mountains – Trimble Surveys – Pumlumon

20.04.14  Cefn Penarth (SN 924 853)

Cefn Penarth (SN 924 853), bwlch on right near to farm and the summit on the left

I’d spent some time the previous evening trying to find two or three hills of interest whose P30 status needed checking or whose Sub status stood a chance of being promoted to a P30.  One that met the latter description was a hill on a descending easterly ridge to the south of Llyn Clywedog.  To make things easier the ridge that the hill is situated on has a minor road following its crest.  However, there are farms either side of the bwlch and summit and it looked like prime sheep grazing land, and as it is now just past lambing time, these little beasts may be with their mothers on the fields I wanted to survey, so I had to show caution and respect toward the beasties.

The road from my last hill (Pt. 381.7m SN 926 875) heads south-eastward toward Llanidloes, after a mile I turned right and then a few minutes later I turned left on to a steep and seldom used road with unenclosed fields on my right, lambs scampering about and three gates to open.  I tried my utmost to encourage the lambs to stay in their given fields when opening these gates, but I’m afraid one escaped in to a neighbouring field, so no doubt she is now wandering around trying to discover a new mother.

I parked beside the track entrance that leads down to the Upper Cefn-penarth farm (SN 920 855).  I’d looked at this road on the digitised Google Map the previous evening and noted ground ground immediately to the north of the road where a 288m spot height appears on Ordnance Survey maps was higher.  I’d also zoomed up the lane toward the summit where a 317m spot height appears on the OS map.  The high point of the hill was above this road.  Could the height difference between the land at the bwlch and summit be sufficient for P30 status to be confirmed?

The 288m spot height appears on this lane, the critical bwlch is higher and in the field on the right

Once out of the car I walked westward up the road to acclimatise myself with the lay of the land at the bwlch, the ground immediately north of the lane proved higher, I looked around for any farm vehicles on adjacent fields and sneaked over the fence, saying good morning to two small lambs and their mother as I did so.  No sooner was I in the field and one of these lambs walked toward me and nuzzled my leg, I ignored its advances!

I needed to be quick as I was in full view of the lane and the Upper Cefn-penarth farm was only over the lip of the field, I spent a few minutes on my knees judging the lay of land, picked my spot and set the Trimble to gather data.  Once the Trimble had been activated I headed to the nearby hedge and sat in the field below it and next to a particularly dense covering of hedgey stuff.  Within a couple of minutes the rumbles of a vehicle from the farm came up the lane, oh gawd, imagine trying to explain what I was doing.  I waited for it to pass and then hoped it wouldn’t turn right, as if it did I would be in full view of the occupant as they passed the fence I had clambered over.  Thankfully they turned left and headed up the lane toward the summit of the hill.  Once five minutes of data were collected I quickly packed the equipment away and walked up the lane to a gate just over the crest of the hill, which gave access to the summit field.

The Trimble GeoXH 6000 set-up position at the bwlch of Cefn Penarth with the Llyn Clywedog dam in the background

Looking up the lane toward the summit

I gathered three data sets from the summit area of the hill, one from what I judged to be the high point, one from the high point near to the road and the third from the high point of an earthen embankment that ran parallel to the road.  In all fifteen minutes of data were collected from these points and the same amount of time was probably spent setting the equipment up, during which I wandered around in a field, next to a road, hoping that no farmer’s vehicle would pass me.  The only one I could see was a quad bike on a lower field; I tried to keep out of his line of sight.

The Trimble GeoXH 6000 gathering data at the second point on the summit area, the high point of the hill is to the left

By 10.55am I was back at the car and travelling toward Llanidloes and then Welshpool.  Soon after arriving home the predicted rain arrived.  A great morning, only done because I’d mistakenly visited the lower top of Dinas two days previously, so I had to re-visit to get another data set. 

LIDAR image of Cefn Penarth

POSTSCRIPT:

Since this hill was Trimbled, LIDAR has become available and summit analysis undertaken by Joe Nuttall and sent to DoBIH prompted me to compare the Trimble result to that ascertained from LIDAR.  The Trimble result is 0.07m lower for the summit compared to LIDAR, but with an approximate 16 metre difference in summit position and a 7 metre difference in bwlch position, the LIDAR result is being prioritised.  

Survey Result:

Cefn Penarth (significant name change)

Summit Height:  318.9m (LIDAR)

Summit Grid Reference:  SN 92415 85333 (LIDAR)

Bwlch Height:  288.9m (LIDAR)

Bwlch Grid Reference:  SN 92025 85612 (LIDAR)

Drop:  30.0m (LIDAR) (Sub-Trichant reclassified to Trichant)

Dominance:  9.41% (LIDAR)

For further details please consult the Trimble Survey Spreadsheet