Saturday, 11 January 2014

Mapping Mountains – Trimble Surveys – Fforest Glud

11.01.14  Cefn Perfa (SO 173 579)

This is the first of two Trimble surveys of Cefn Perfa, to read the post on the second survey please click {here}

Cefn Perfa (SO 173 579).
Cefn Perfa rises above the small community of Llanfihangel Nant Melan and is rather forgetfully placed with higher neighbours all around.  Nowadays it is a pastoral field with the customary barbed wire fences and a few points of access via gates from its south.

The hill has an elongated shape to it with its critical bwlch placed between two lakes, one is a body of water named Llyn Heilyn, whilst the other is a smaller affair and is full of reeds and is named Hanover Pool.

Llyn Heilyn with The Van (SO 162 587) on right of photo.
From bwlch to summit is no more than 5 – 10 minutes.  As the day’s forecast was for winter sunshine I decided to re-visit Cefn Perfa and determine an accurate drop value for the hill.  I’d only visited once before on the 23rd September 2003 and surveyed the hill’s drop using my old staff.  The result came to 97ft / 29.6m, therefore I never included it in the Welsh 400m P30 list now known as Y Pedwarau, but Clem gave it 30m of drop and included it in his listings, likewise Mark Jackson.  My brief notes for the day have ‘Easy measure over fence, a lane and another fence to close cropped grassy summit, Clem has this hill’s drop as 30m’.

I planned to visit three hills during the day and survey each summit and critical bwlch, therefore I wanted a relatively early start and was at the base of Cefn Perfa by just after 9.00am.  Shortly after I was at its summit and assessed the highest point from a number of angles, choosing my spot I set the Trimble on the ground and left it gathering data for six minutes.  Early morning light cast long shadows over the grass as a bird of prey gained height over the valley, sheep gatherers were out on their quad bikes on adjacent hills rounding up the small white flecks and bringing them down to new pasture.

A good perspective showing the Trimble on the high point of Cefn Perfa.
The Trimble GeoXH 6000 on the summit of Cefn Perfa.
Once the Trimble had been packed away I was down at the bwlch within a few short minutes.  The point of the critical bwlch is easily identifiable and is within a few metres of the lane.  Again the Trimble was set up and I happily lazed about taking photographs and enjoying the stillness of the morning.  Just on the north of the hill is the A44, a relatively busy road for this part of Wales.  However, on its south everything is peaceful and quiet and this morning there was only an occasional vehicle passing, a few raised hands as acknowledgement when a car did pass, but no one disturbed me and I quietly went about gathering another six minutes of data.

At the critical bwlch with Llyn Heilyn in the background.
A quick stride over the fence and a brisk walk back down the lane brought me to the car.  Next stop was Whimble.

Survey Result:

Cefn Perfa

Summit Height:  411.2m (converted to OSGM15)

Summit Grid Reference:  SO 17389 57972

Bwlch Height:  381.2m (converted to OSGM15)

Bwlch Grid Reference:  SO 17288 57783

Drop:  30.0m

Dominance:  7.31% (based on data from second survey)

As the 30m (30.037m) drop value has an accuracy of +/- 0.1m the result is within the margin of uncertainty of the technology used.  Therefore, before reclassification to Pedwar status can take place it is hoped that a line survey can be conducted to determine the drop of this hill.

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

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