Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

Bryn Gwyn (SJ 213 617)

There has been a Significant Height Revision to a hill that is listed in the Y Trichant – The 300m Hills of Wales, with the summit height and its position confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and which took place on the 18^th December 2019.

Gathering data at the the summit of Bryn Gwyn (SJ 213 617)

The criteria for the list this height revision affects are:

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017.

The name the hill is listed by is Bryn Gwyn and it is adjoined to the Moel y Gamelin group of hills, which are situated in the north-eastern part of North Wales (Region A, Sub-Region A2), and it is positioned with the A494 road to its north and minor roads to its west, south and east, and has the village of Gwernymynydd towards the north.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website the summit height of this hill was listed as c 335m which was based on a non-interpolated height of its uppermost contour that appears on Ordnance Survey 1:25,000 Explorer maps.

Extract from the Ordnance Survey 1:25,000 Explorer map

After the P30 lists were standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and gave a 339m summit height for this hill.  The 339m summit spot height also appears on Ordnance Survey data available on the Magic Maps website.

Extract from the Magic Maps website

The summit height produced by the Trimble GeoXH 6000 is 338.6m and is positioned at SJ 21352 61727, this is not a dramatic height revision when compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, this hill’s new listed summit height is 338.6m and this was derived from a Trimble GeoXH 6000 survey, this is 3.6m higher than the non-interpolated c 335m summit height that was previously given for this hill.

The full details for the hill are:

Group:  Moel y Gamelin

Name:  Bryn Gwyn

OS 1:50,000 map:  117

Summit Height (New Height):  338.6m (converted to OSGM15)

Summit Grid Reference:  SJ 21352 61727

Bwlch Height: c 302m (interpolation)

Bwlch Grid Reference:  SJ 21258 61471 (interpolation)

Drop:  c 37m (Trimble GeoXH 6000 summit and interpolated bwlch)

Myrddyn Phillips (April 2020)

Mapping Mountains – Trimble Surveys – Moel y Gamelin

18.12.19  Bryn Gwyn (SJ 213 617) and Moel Findeg (SJ 209 611)  

Moel Findeg (SJ 209 611)

Having visited the summit of Mynydd Du (SJ 214 571) I drove the short distance north and parked beside a farm between the two hills of Bryn Gwyn to the north, and Moel Findeg to the south.  Closing the car door I noted a public footpath leading toward the latter hill and then called at the farm to ask permission to park, this was duly granted.

The early morning clag was breaking which gave an occasional glimpse of the world beyond the greyed immediate scene.  A track a few metres back down the road led up the westward side of my next hill; Bryn Gwyn.  I soon left the track and followed vehicle tracks up a field which took me around the east side of the upper part of the hill.

Mist and murk still clung at this height with shapes of gorse patches and trees forever springing up in to view and gently disappearing again.  I’d read reports on the Hill Bagging website that the summit of Bryn Gwyn is immersed in gorse and I wondered if it could be Trimbled.  I was soon below the gorse which extended across the upper part of the hill which consists of an attractive knolled ridge.  My second attempt at getting to the summit succeeded having given up on my first which led me to a high 10ft wall of gorse which looked forbidding.

Having found a way through the gorse I crested the upper ridge at the summit which steeply fell away a few metres on its eastern side.  Thankfully the high point was free of gorse and therefore positioning the Trimble at the summit atop my rucksack was relatively easy, and within a few minutes it was quietly beeping away gathering data as I stood below it amongst gorse waiting patiently for the allotted data to be stored.

Gathering data at the summit of Bryn Gwyn

Once data gathering were completed I packed the equipment away and followed another vehicle track on the western side of the gorse laden upper part of the hill back to my inward route, and then followed this down to the minor road and the public footpath sign close to where my car was parked.

The public footpath led up a track to grazing fields and more gloomed murk with nearing silhouettes of steep sided summits springing in to view as I followed the path upward.  This route brought me quickly to the base of the upper part of Moel Findeg which consists of an attractive steep sided crag with the continuation of the path leading up grass to its high point.

I placed the Trimble on the ground with its internal antenna aligned to the highest bit of the hill and stood below and to the west of it, as it gathered its allotted data.  By now the early morning breeze was as forecast, as its strength increased.  As the Trimble gathered data I looked west and the clag had been pierced with the higher Clwydian hills emerging from out of their murk, but still to the east the low clag hung in a dense grey murk.

Gathering data at the summit of Moel Findeg

The Trimble set-up position at the summit of Moel Findeg

After packing the equipment away I took a few photos and made my way down the path and looked back on the upper crag.  Moel Findeg is a fine small heighted hill and one that was saved by the local community who purchased the hill saving it from the ravages of impending quarrying.  Once back at the car I watched as two chickens squawked their way toward me, I said my hello’s and hoped they had moved as I slowly drove away toward my last hill of the day; Hafod Mountain (SJ 211 630). 

Survey Result:

Bryn Gwyn 

Summit Height:  338.6m (converted to OSGM15, Trimble GeoXH 6000) (significant height revision)

Summit Grid Reference:  SJ 21352 61727 (Trimble GeoXH 6000)

Bwlch Height:  c 302m (interpolation)

Bwlch Grid Reference:  SJ 21258 61471 (interpolation)

Drop:  c 37m (Trimble GeoXH 6000 summit and interpolated bwlch)

Dominance:  10.82% (Trimble GeoXH 6000 summit and interpolated bwlch)

Moel Findeg 

Summit Height:  365.0m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SJ 20955 61181 (Trimble GeoXH 6000)

Bwlch Height:  c 309m (interpolation)

Bwlch Grid Reference:  SJ 20691 60689 (interpolation)

Drop:  c 56m (Trimble GeoXH 6000 summit and interpolated bwlch)

Dominance:  15.35% (Trimble GeoXH 6000 summit and interpolated bwlch)

For further details please consult the Trimble Survey Spreadsheet