Mapping Mountains – Trimble Surveys – Moel Hebog

30.12.13  Foel (SH 450 506)

This is the first of three Trimble surveys of Foel, to read the post on the second survey of Foel please click {here} and the third please click {here}

Foel (SH 450 506).

Although west of the A487 road, Foel (SH 450 506) is adjoined to Crib Nantlle and therefore part of the Moel Hebog group of hills.  It is listed as a Sub-HuMP and a Welsh 200m P30 with c 99m of drop.

 

Visiting this hill was somewhat rushed as I planned to look at one or two hills above Blaenau Ffestiniog, but after waiting almost two hours for the rain to stop I gave up and headed towards Nantlle where the murk and wetness had already cleared eastward.  With only an hour or so of daylight remaining options were limited, but Foel was feasible in the time left before darkness and when approaching the hill from the south-east its bwlch is on the way up to its summit.

I had a quick look at the area of the bwlch on my way up the track that goes to Llwyn Bedw Uchaf, the track seemed to be where the critical bwlch was placed, and this also matched what contour interpolation suggested on the map.

The whole hillside was sodden due to the heavy and persistent rain that north-west Wales had been experiencing for a number of days.  The upper section of the hill has the remains of an ancient hill fort on it.  I placed the Trimble on the ground beside the cairn, having dug down beyond the grass creating a flatbed for it to nestle in.  The sun was just disappearing behind the higher hills of Yr Eifl and after five minutes of data collection I was away and down to the area of the bwlch as quickly as my legs could take me.

The Trimble beside the cairn on the summit of Foel.

Grass has now grown over many of the lower rocks of the summit cairn.

I took two readings from the bwlch area, one beside the track which seemed to be the high point of the valley to valley traverse and which also followed the direction of the hill to hill traverse, and a second reading in an adjacent field beside a large puddle of standing water.  By the time I got back to my car I just had enough time to change before darkness set in. 

Trimble in field next to standing water.  The hedge (left) and track (upper centre) give an inclination toward where the low point of the hill to hill traverse is positioned.

The Trimble beside the track that crosses the critical bwlch.

Same position, but different view of the Trimble beside the track that crosses the critical bwlch.

Survey Result:

Foel

Summit Height:  221.4m (converted to OSGM15)

Summit Grid Reference:  SH 45022 50673

Bwlch Height:  120.6m (converted to OSGM15)

Bwlch Grid Reference:  SH 45818 50104

Drop:  100.9m 

Dominance:  45.56% (final 3rd survey gives 45.72% Dominance)

An interesting result, as if confirmed this hill will be a new Welsh Hump.  However, the Trimble was activated before the recommended 0.1m accuracy had been attained during the survey of the bwlch and the standard deviation shows a relatively high figure of 0.7m and the estimated accuracy is also poor.  The second point surveyed at the bwlch, which was in the adjacent field, has 0.0m for standard deviation and a good estimated accuracy with an absolute height of 119.9m, indicating the height of the bwlch to be on the low side when compared to its c 120 – c 130 map contouring.

For further details please consult the Trimble survey spreadsheet click {here}