Sunday, 29 December 2013

Mapping Mountains – Trimble Surveys – Mynydd Hiraethog

24.12.13  Dinas Mawr (SH 808 539), Gallt y Celyn (SH 811 542) and Gallt y Celyn (SH 810 544)

Dinas Mawr (SH 808 539)

One of the advantages of having the Trimble is being able to accurately survey hills such as the ones visited today.  With G&J Surveys prioritising English and Welsh marginal Marilyns and high prominence Sub-Marilyns, English and Welsh Nuttalls and continuing with our visits to Scotland, and with Alan Dawson concentrating on Scottish Marilyns, Sims and the occasional Hump, and with John Fitzgerald roaming around a multitude of Irish hills, it means that many parts of Wales and an occasional visit in to England with the Trimble can produce accurate data on hills that none of the above will visit.  Today was a prime example as I wanted to confirm the status of Dinas Mawr as it was originally listed as a Sub in the Welsh 200m P30 list, and was later promoted to P30 status through contour interpolation, this hill also has an adjacent P30 twin top, so I wanted to de-twin this hill as well.

The three summits are on open access land and are easily approached from a bridleway just above the A5.  The higher hills to the west and south were bathed under winter grey cloud, this heralded the heavy showers that were forecast and as I made my way through a gate toward the bwlch of Dinas Mawr the first of these hit me as a vicious hail shower.

The going under foot was problematical as small trees interspersed with bracken and copious amounts of bramble made for rather slow progress.  I assessed the point of the bwlch from various angles, chose my spot and gathered five minutes of data before heading up through the bracken and rock outcrops toward the summit of Dinas Mawr.

The top is crowned by a few quartz rocks and marks the highest point of a fine hill; I removed the quart cairn and set the Timble up to gather data.  I soon had to turn it off as the fierce wind was making it wobble, I re-started it after wedging a small quartz rock on the leeward side of the equipment.
The Trimble GeoHX on the summit of Dinas Mawr.

The route from this summit to the next proved torturous as I decided on a direct line that took me in to a forest of bramble.  After negotiating the slippery rock of a stone wall I headed up to the first of the 258m twin map height tops.  The high point consists of a long rock outcrop.

Looking back toward Dinas Mawr from Gallt y Celyn (SH 811 542).

By now more hail showers were massing and the next hit me as I was on the second 258m twin summit.  This consists of long grass on top of a large boulder.  The descent route was back on the inward track with the wind drying my clothes on the way.

The Trimble on the summit of the second of the 258m map heighted twin summits (SH 810 544)

Survey Result:

Dinas Mawr

Summit Height:  254.0m (converted to OSGM15)

Summit Grid Reference:  SH 80884 53931

Bwlch Height:  220.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 80984 53980

Summit Height:  257.6m (converted to OSGM15) 

Summit Grid Reference:  SH 81121 54259

Drop:  30.1m (converted to OSGM15) (200m Sub-Twmpau re-instated as 200m Twmpau after surveying the bwlch)

Dominance:  11.68%

Gallt y Celyn

Summit Height:  257.1m (converted to OSGM15)

Summit Grid Reference:  SH 81007 54476

Drop:  14m

Dominance:  5.45%

For the post detailing the bwlch survey of Gallt y Celyn please click {here}

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

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