Mapping Mountains – Trimble Surveys – Moel Hebog

24/25.12.13  Y Garreg (SH 557 537) and Bryn Gwyn (SH 556 534)

Y Garreg (SH 557 537)

Daylight was quickly disappearing as I gathered data beside the high point of the minor road between Rhyd-ddu and Nantlle.  This is named Bwlchgylfin (SH 555 533) and is the critical bwlch for Y Garreg.  I’d only visited Y Garreg once before and had a distant memory of its summit being fun finding a way off of it.

After the Trimble was packed away I set off around the western side of Llyn y Dywarchen toward the steep southerly slopes of Y Garreg.  By the time I’d reached its summit dusk was upon me and a gale was blowing with ferocious hale showers adding to the fun.  I hesitantly placed the Trimble on the highest rock and watched as the wind rolled it over, this happened two or three times so I decided the safest thing to do was lie down beside it and hold it whilst the wind howled and a bombardment of hail hammered down on me.

The Trimble GeoXH 6000 on the summit of Y Garreg.

After five minutes of data collection I closed the Trimble off and headed down.  I decided against my upward route as I didn’t want to attempt the descent on one delicate foot placement on steeply angled rock.  Therefore I slithered down on steep, wet grass.

Before the festivities of the next day commenced I headed back up to Llyn y Dywarchen and visited the bwlch between Y Garreg and Bryn Gwyn.  This proved very wet, after gathering data I headed up to the summit of Bryn Gwyn and gathered data at two points, both close together.  This is when having a level and staff is a major advantage as the high point could easily be found.  Using just eyesight is not ideal, but as the Trimble only requires five minutes of data for an accurate result it can at least, be placed on a number of points in quick succession.

Early morning at the bwlch between Bryn Gwyn and Y Garreg.

One of the two positions for the summit of Bryn Gwyn.

I then wanted to continue what I’d started the previous day and look at more points for the prospective critical bwlch position of Mynydd Mawr.  But that's for the next blog posting.

LIDAR image of Y Garreg (SH 557 537)

Survey Result:

Y Garreg

Summit Height:  336.8m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 55729 53707 (Trimble GeoXH 6000)

Bwlch Height:  245.5m (LIDAR)

Bwlch Grid Reference:  SH 55528 53380 (LIDAR)

Drop:  91.3m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  27.10% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Bryn Gwyn

Summit Height:  291.3m (converted to OSGM15)

Summit Grid Reference:  SH 55653 53435

Bwlch Height:  256.9m (converted to OSGM15)

Bwlch Grid Reference:  SH 55681 53596

Drop:  34.5m

Dominance:  11.83%

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