Mapping Mountains – Summit Relocations – 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales

Plas Gwyn (SH 524 817)

There has been a Summit Relocation to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, its location, the drop and status of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter taking place on the 22^nd October 2018.

Plas Gwyn (SH 524 817)

The criteria for the two listings that this summit relocation applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol - The Dominant Hills of Wales - Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height, with the Introduction to the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name of the hill is Plas Gwyn and this was derived from local enquiry, and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it has the A5025 road to its west and the coast to its north and east, and overlooks Traeth-coch (Red Wharf Bay) to its south-east, and has the village of Benllech towards its north-west.

This hill was first listed in the original Welsh 30-99m P30 list published on Geoff Crowder’s v-g.me website with a 78m summit height positioned at SH 526 817 and which is based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website with the cursor indicating the position of the newly relocated summit

Prior to the Trimble GeoXH 6000 summit survey the details for this hill were analysed with LIDAR.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR image of the summit of Plas Gwyn

The height produced by LIDAR analysis and the Trimble GeoXH 6000 summit survey is 76.1m which is positioned at SH 52494 81743, this is not a dramatic difference in position compared to some relocations, but it does come within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

The Trimble GeoXH 6000 gathering data at the new summit position of Plas Gwyn

The Trimble GeoXH 6000 gathering data at the old summit position of Plas Gwyn

Therefore, the summit height produced by the Trimble GeoXH 6000 survey is 76.1m and is positioned at SH 52494 81743, this position is not given a spot height on contemporary Ordnance Survey maps and is approximately 110 metres west from where the 78m spot height appears on the Ordnance Survey 1:25,000 Explorer map and which was the position of the previously listed summit and surveyed as being 75.7m in height.

The full details for the hill are:

Group:  Ynys Môn

Name:  Plas Gwyn

OS 1:50,000 map:  114, 115

Summit Height:  76.1m (converted to OSGM15)

Summit Grid Reference (new position):  SH 52494 81743

Bwlch Height:  41.9m (LIDAR)

Bwlch Grid Reference:  SH 52209 81404 (LIDAR)

 

Drop:  34.2m (Trimble summit and LIDAR bwlch)

Dominance:  44.91% (Trimble summit and LIDAR bwlch)

For details on the survey that confirmed the summit relocation of this hill

Myrddyn Phillips (May 2019)

Mapping Mountains – Significant Name Changes – 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales

Plas Gwyn (SH 524 817)

There has been a Significant Name Change to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, its location, the drop and status of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter taking place on the 22^nd October 2018.

Plas Gwyn (SH 524 817)

The criteria for the two listings that this name change applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol - The Dominant Hills of Wales - Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height, with the Introduction to the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The hill is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it has the A5025 road to its west and the coast to its north and east, and overlooks Traeth-coch (Red Wharf Bay) to its south-east, and has the village of Benllech towards its north-west.

This hill was first listed in the original Welsh 30-99m P30 list published on Geoff Crowder’s v-g.me website, under the partly transposed and invented name of Moel Castell Mawr, with an accompanying note stating; Name from remains of castle to the South-East.

Moel Castell Mawr

78m

SH526817

114/115

263

Name from remains of castle to the South-East

During my early hill listing I thought it appropriate to either invent a name for a hill, or use a name that appeared near to the summit of the hill on Ordnance Survey maps of the day.  My preference was to use farm names and put Pen, Bryn or Moel in front of them or as in this instance transpose the name of what I presumed to be a castle and prefix it with the word Moel.  This is not a practice that I now advocate as with time and inclination place-name data can be improved either by asking local people or by examining historic documents, through this form of research an appropriate name for the hill can usually be found.

The Trimble GeoXH 6000 gathering data at the summit of Plas Gwyn

After visiting this hill I called at the Plas Gwyn Caravan and Camping Park which is situated just below the hill to the south and met David Bennet who explained that the land taking in this hill is owned by Michael Buckley, David kindly directed me to Michael’s home, which I called out twice over the following few days without any reply.  However, on my first visit I met Mark Griffith who was trimming a hedge and he kindly gave me a contact telephone number for Michael.  When I contacted Michael he explained that the hill has been owned by his family for many years and that it is known after that of the farm, Plas Gwyn. 

Therefore, the name this hill is now listed by in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales is Plas Gwyn, and this was derived from local enquiry.

The full details for the hill are:

Group:  Ynys Môn

Name:  Plas Gwyn

Previously Listed Name:  Moel Castell Mawr 

OS 1:50,000 map:  114, 115

Summit Height:  76.1m (converted to OSGM15)

Summit Grid Reference:  SH 52494 81743

Bwlch Height:  41.9m (LIDAR)

Bwlch Grid Reference:  SH 52209 81404 (LIDAR)

 

Drop:  34.2m (Trimble summit and LIDAR bwlch)

Dominance:  44.91% (Trimble summit and LIDAR bwlch)

For details on the summit survey of this hill

Myrddyn Phillips (May 2019)

Mapping Mountains – Trimble Surveys – Mynydd Twr

22.10.18  Plas Gwyn (SH 524 817)  

Plas Gwyn (SH 524 817)

This hill is perched above the eastern coastline of Ynys Môn and looks out over Traeth Coch (Red Wharf Bay) and across to the forested summit of Mynydd Llwydiarth and the limestone encrusted summit of Bwrdd Arthur.  Prior to my visit I had analysed its summit and bwlch with LIDAR and now wanted an on-site visit to bag its summit and take two data sets; one from where LIDAR gives its high point to be situated and the other at a fence junction where the summit is reported to be situated on the Hill Bagging website.

I parked opposite a public football beside the A 5015 as it makes its way between Pentraeth and Benllech.  After spending the morning and early afternoon visiting four P30s dotted across the south-eastern part of the island, many of which were tucked away with the nearest access being narrow country lanes, it felt unusual to encounter fast moving traffic seemingly hurtling past going who knows where.  After waiting for a number of cars and lorries to pass I made my way over the strip of tarmac and through a kissing gate to instant tranquillity and other worldliness as an enclosed old green lane made its way south-eastward up the lower southern part of this hill.

As height was gained a gate gave access to the manicured grazing field on my left, this stretched out toward the high point of the hill, and with beautiful afternoon blue sky above and a slight warmth, and with no one about, it seemed I had the hill to myself, even sheep were absent.

I followed a boundary fence until a gap gave access to the large field toward where the high point of the hill is situated.  Approaching from the south gave me chance to examine the lay of land as I neared the summit and to me it was relatively obvious where its high point lay, once there I compared my position against the ten figure grid reference that the Trimble gave and it matched the LIDAR summit to within one metre.

Gathering data at the summit of Plas Gwyn (SH 524 817)

Having set the Trimble up and activated it to gather data I walked over to the fence boundary where the high point has been reported to be situated.  This part of the hill rises more steeply compared to where LIDAR gives the summit to be placed.  I spent a number of minutes examining this part of land and decided that a second data set was necessary.

The Trimble set-up position at the summit of Plas Gwyn (SH 524 817)

Once the Trimble had gathered and stored data from the LIDAR summit I set it up on what I judged to be the highest natural land beside the fence and again waited for the allotted data to be gathered.  During this I again examined this part of land and realised that the Trimble was placed on what looked like the remains of an old boundary that is slightly raised, but this is not shown as such on the Tithe map.

Gathering data at the second Trimble set-up position

It was a delight to wait for these two data sets to be collected as the weather was blissful with wisps of high cloud accentuating the blueness of sky.  Once the Trimble was packed away I wandered back down the hill to another gate giving access on to the public footpath and then continued on it toward the Porthllongdy Caravan Site where I met David Bennet.  David didn’t know the name of the hill or the field name where its summit is situated, but said if anyone knew it would be Michael Buckley who owns this land.

David directed me to Rhiwlas; Michael Buckley’s home, where I knocked on several doors, unfortunately no one was in, but I did meet the hedge cutter who kindly gave me a forwarding telephone number to make further enquiries.  Once contacted, Michael gave me the name of Plas Gwyn for the hill, with it taking its name from the farm to its south.        

Survey Result:

Plas Gwyn (significant name change)  

Summit Height:  76.1m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 52494 81743 (Trimble GeoXH 6000) (summit relocation confirmed)

Bwlch Height:  41.9m (LIDAR)

Bwlch Grid Reference:  SH 52209 81404 (LIDAR)

Drop:  34.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  44.91% (Trimble GeoXH 6000 summit and LIDAR bwlch)

For further details please consult the Trimble Survey Spreadsheet