Mapping Mountains – Trimble Surveys – Hirddywel

09.02.14  Coed y Gaer (SO 004 843)

Coed y Gaer (SO 004 843)

After getting wet on Oldchapel Hill (SN 976 807) we visited the Red Lion in Llanidloes for its £5.00 carvery and then ventured outside to more rain.  It really was YUCK!!

We did have a brief conversation that centred around a large mug of tea and a slice of winter berry cheesecake in the comfort of my house in Welshpool, but we decided on driving as far as the start of the proposed second walk of the day, just to have a look and see if the rain would stop.

Rather stupidly the rain did stop and gave us encouragement that the predicted dry spell of weather had arrived.  We parked close to where a disused quarry is marked on the map at SO 002 841.  Mark’s initial plan was a there and back walk visiting both Moelfre (SN 995 829) and Coed y Gaer (SO 004 843), but as daylight hours were now against us it meant that only one of the hills was feasible and we opted for Coed y Gaer, a hill I hadn’t visited before.

The hill side above us was steep from all angles and when we set off uphill we were soon slithering downhill on steep slopes made up of wet mud; rather perversely I thought it reminiscent of a new winter mud sliding sport.

Mark on the steep slopes of Coed y Gaer with Moelfre (SN 995 829) in the background

The encouragement of the all too short dry patch of weather was soon forgotten as more bitterly cold heavy squalls of rain battered across the land.  Slowly progress was made on the steepening slopes; two fences were negotiated which gave access to the upper section of the hill.  This was very wet and as the last few metres led to the summit wet snow was falling from above.

By now my thicker winter gloves were sodden and exposing fingers to set the Trimble up on its pole adjacent to the high point of the hill was a thankless task as they ended up screaming cold once again.  The weather really was foul!

A mass of grey murk battered us when we arrived at the summit of Coed y Gaer

The equipment was set up about 7cm below the very highest point, which is in the centre of the ridge fence that also has broad fence posts in proximity and a three metre high metal pole nearby.  It’ll be interesting to see if data collection was disturbed by so many near obstacles.

During the time when the equipment was being set up and my fingers screamed with cold, Mark stood passively with his back to the rain overlooking a storm laden Severn valley.  Across the river stood Y Gaer (SO 013 873) and Gelli Hir (SN 999 883) the Twin HuMP I’d visited two days ago.  By the time the 10 minutes of data collection was almost finished the wet weather had sped down the Severn valley and the sun was bursting through the cloud.

The Trimble was set up about 7cm below the highest point (which is in the centre of the fence) to try and keep its satellite coverage clear of the fence posts and metal pole

YYYIIIPPPPEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE - sunshine!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

We headed directly south from the summit and slowly made our way down increasingly slippy slopes, Mark aimed for the car and was patient enough to allow me time to investigate the area of the bwlch.  This was just around the bend in the narrow lane.

I wanted to get data from two positions at the bwlch as contour interpolation suggests the critical bwlch is placed adjacent to a stream that ‘issues’ forth from under a road at SO 00532 83919.  When I walked to this point it was evident that the road continued its downhill progress to where a 241m spot height appears on the Ordnance Survey enlarged Geograph map at SO 00512 83885.

A very expensive accident waiting to happen - the Trimble gathering data in the centre of a road

I gathered five minutes of data from each, with the second position having the Trimble placed in the centre of the road away from the bordering hedge on either side.  It took an age to achieve its required 0.1m accuracy before activating it to gather data.  Shortly after it had gathered its five minutes of data a truck appeared on the road, a few minutes earlier and the Trimble may have ended up as road kill!

The day had proved excellent, albeit a bit wet.  Great to see Mark again, visit a couple of hills with one being a new P30 for me, and an hour away from the wet stuff in the pub with a good meal.

LIDAR summit image of Coed y Gaer (SO 004 843)

LIDAR bwlch image of Coed y Gaer

Postscript:  Since the survey of this hill LIDAR has become available.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.  Consequently the details for Coed y Gaer have been analysed via LIDAR and it is this result that is being prioritised.  With LIDAR contouring able to pinpoint the natural bwlch of this hill, and this is being used in preference to the artificially raised road.

Survey Result:

Coed y Gaer

Summit Height:  361.0m (LIDAR) (significant height revision)

Summit Grid Reference:  SO 00491 84393 (LIDAR)

Bwlch Height:  239.5m (LIDAR)

Bwlch Grid Reference:  SO 00523 83853 (LIDAR)

Drop:  121.5m (LIDAR)

Dominance:  33.65% (LIDAR) (Lesser Dominant addition)

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