Wednesday, 28 October 2015

Mapping Mountains – Trimble Surveys – Bryniau Clwyd

10.10.15  Bryn y Baal (SJ 259 647, to base of rock bluff)  

Bryn y Baal and its rock bluff

There’s nothing quite like splitting a twin map heighted top, all the nonsense is then solved with no more debate, however I quite like some of this nonsense and it would be a shame to solve every twinned top problem as some should be left for future generations.

I didn’t even now that we were going for an early morning little twin topped adventure until I was in the car with Mark and he was driving south-east from his house in Sychdyn.  We’d driven past this spot before as this little problem is one that Mr Trengove is particularly enthusiastic to solve.  On this previous occasion Mark explained that Bryn y Baal is given a spot height of 172m on the Ordnance Survey enlarged Geograph map and the high point of this hill is a rock bluff in the back garden of quite a large house, whilst 1 km further south-east is another 172m high point called Prenbrigog (SJ 266 640) which has its summit either at the back of, or at the side of a farm house.

One small Trimble and one large house.  I wonder if the occupant will give permission to survey the high point of their garden?

Mark had investigated the area below the large house at Bryn y Baal where until recently a high fence festooned with ‘No Climbing’ signs had attempted to dissuade any P30 baggers from a below the rock bluff approach, this approach is not recommended as a rope would be required for all but the most competent of climber.

The area below the rock bluff had recently been altered as there is now a two metre high chain link fence with a gate and accompanying locked combination padlock, with the area situated away from the immediate surrounds below the rock bluff now having a local amenity area with a nature reserve and an information board.  However, of most interest was where the spot height appeared on the map, this was positioned at the bottom of the rock bluff beside the fenced off area, if the height and position of this 172m spot height proved correct, the summit of Bryn y Baal would be approximately 7m higher, and if this was so, then Bryn y Baal would be the higher of the current twin tops.  All that was needed was an accurate height measurement taken to where the 172m spot height appears on the ground.  Mark had already obtained a 168m reading at this point with his hand-help GPS which consistently gives readings between +3m - +5m above the actual height.  Confirmation was needed and as I tried to wake up in the passenger seat and work out where we were going and why, we arrived, and Mark directed me toward the base of the rock bluff and said ‘get the Trimble up and running as we don’t have much time’.  This statement referred to our pre-arranged meeting with John Kirk in Sedbergh and if the Trimble didn’t attain its 0.1m accuracy level quickly we would be late.

The surrounding land at the base of the rock bluff

As I set the Trimble up on top of my rucksack we discussed the height difference between the ground at the base of my rucksack and the high point of the rock bluff and estimated this to be 7m, with a margin of uncertainty for height difference to be +/- 1.5m.

It took the Trimble about ten minutes for it to attain its 0.1m accuracy level and once it did I pressed ‘Log’ and wandered around taking a few photographs of the scene.  As the last of the 300 data points were collected I pressed ‘Done’ and packed the equipment away and joined Mark beside his car for our journey north to meet Mr Kirk.

Survey Result:

Bryn y Baal

Summit Height:  171.5m (converted to OSGM15) (approximate value from 

164.5m survey to base of rock bluff)

Summit Grid Reference:  SJ 25902 64765 (to base of rock bluff)

Drop:  c 50m

Dominance:  29.16%

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

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