Mapping Mountains – Significant Height Revisions – Y Pedwarau

Bryn Melyn (SO 109 184)

There has been a Significant Height Revision to a hill listed in the Y Pedwarau initiated from a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted on the 22^nd July 2014.  With the criteria for Pedwar status being all Welsh hills at or above 400m and below 500m in height that have a minimum 30m of drop.

The name of the hill is Bryn Melyn and it is situated in the Bannau Brycheiniog (Brecon Beacons) range of hills in south Wales, with the survey of the hill conducted in the company of Mark Trengove who had suggested the walk.

Bryn Melyn can be easily accessed from the end of a minor road above the waters of the Talybont Reservoir which is situated in Glyn Collwn.  The hill can also be accessed from its opposing valley of Dyffryn Crawnon which gives a slightly more rewarding and lengthy walk.

This hill's summit height has been increased from its current Ordnance Survey map height, as prior to the survey with the Trimble GeoXH 6000 the hill was listed with an estimated summit height of c 446m based on it having an uppermost contour ring of 440m on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  Its new summit height is 450.5m (converted to OSGM15) which is 4.6m higher than its previously estimated height and 10.5m higher than its uppermost ring contour on current Ordnance Survey maps.

The full details for the hill are:

Cardinal Hill:  Pen y Fan

Summit Height (New Height):  450.5m (converted to OSGM15)

Name:  Bryn Melyn

OS 1:50,000 map:  161

Summit Grid Reference:  SO 10941 18432

  

Drop:  38.2m (Trimble summit and LIDAR bwlch)

Gathering data from the summit of Bryn Melyn which resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips and Aled Williams (August 2015)

Mapping Mountains – Trimble Surveys – Cymoedd Gwent

22.07.14  Bryn Melyn (SO 109 184)

Bryn Melyn (SO 109 184)

Bryn Melyn is perched on the southern flank of Tor y Foel (SO 114 194), a small lump of a hill with its grassy summit heading skyward but forever dominated by its higher and more prominent neighbour, it clings on to the hillside almost as an afterthought, something that seems rather inconsequential, but none the less fine views can be had from its summit, especially northward to Tor y Foel and westward to the Talybont Reservoir in the valley below and across to the eastern part of the high Bannau Brycheiniog, with the profiles of Allt Lwyd (SO 078 189) and Waun Rydd (SO 061 206) on grand display.

Talybont Reservoir with Allt Lwyd (SO 078 189) and Waun Rydd (SO 061 206) above and to the right

I’d only visited this hill once before, in early June 2013 when on a four day bagging trip, visiting friends in south and mid Wales whilst enjoying days of endless sunshine and visiting as many hills as my body could get up.  Today’s walk had been suggested by Mark, who had a day off work and wanted to investigate south Wales to edge his second round of the Welsh Hewitts nearer to completion.  Before the main walk he suggested we could visit Bryn Melyn and survey it as the hill is easily visited from a high road that culminates at the hill’s bwlch.  Bryn Melyn is currently listed in Y Pedwarau (Europeaklist May 2013) as a marginal Pedwar with c 446m summit (no spot height appears on any map) and c 413m bwlch, giving c 33m of drop.  As well as determining if Bryn Melyn is rightly listed as a Pedwar we could also give it an accurate absolute height, rather than an estimated one.

We had a relatively long drive down to south Wales as we wanted to avoid the throngs of people enjoying the Royal Welsh Show at Builth Wells, our journey deposited us at the top of the high road at just after 11.30am.  As Mark took photos of the higher hills to the west I had a look at the area of the bwlch, a solid stone wall heads down from just below the summit of Bryn Melyn and crosses the bwlch in the hill to hill direction, land immediately below the wall on its eastern side is significantly higher than that on its western side, this we deemed to have been earth piled up during the walls construction and therefore man-made, therefore we discounted it as the rightful place for the critical bwlch.  Once a position had been chosen the Trimble gathered five minutes of data and we then headed up the hill to the summit.

The first survey for the bwlch position of Bryn Melyn

The ascent of the hill is an easy one with a small sheep path to follow before the high point is gained.  This consists of grass with a few thistles adding summer colour to the profusion of greens.  The summit is easily identifiable and soon had the Trimble placed on it gathering another five minutes of data.  As the data was being stored we pottered about taking photos.

The view south from the summit of Bryn Melyn as the Trimble gathers data

The view north from the summit of Bryn Melyn toward Tor y Foel as the Trimble gathers data

Once the Trimble was packed away we headed down and re-assessed the area of the bwlch and decided to get another data set from a slightly different position, this was next to a large manure heap and rutted ground caused by farm vehicles.  Again the Trimble was placed away from the ground immediately below the wall as this was deemed to have been built up and therefore man-made.  After the Trimble was closed off and packed away we headed down the narrow road and aimed for the car park next to Talybont Reservoir for the main walk of the day.

The second survey for the bwlch position of Bryn Melyn

 

 

Survey Result:

Bryn Melyn

Summit Height:  450.5m (converted to OSGM15) (significant height revision)

 

Summit Grid Reference:  SO 10941 18432

Bwlch Height:  412.3m (LIDAR)

Bwlch Grid Reference:  SO 10976 18733 (LIDAR)

Drop:  38.2m  (Trimble summit and LIDAR bwlch)

Dominance:  8.48% (Trimble summit and LIDAR bwlch)

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