Mapping Mountains – Summit Relocations – Y Trechol – The Dominant Hills of Wales

Clytiau Poethion (SH 763 717)

There has been a Summit Relocation to a hill that is listed in the 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 10^th October 2018.

LIDAR image of Maes Glas Mawr and Clytiau Poethion

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

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 bounded land where the summit of this hill is situated is Clytiau Poethion, and this was derived from the Tithe map and it is the name that this hill is now listed by, and it is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and the hill is encircled by minor roads with the B5106 and the Afon Conwy (River Conwy) to its east, and has the town of Conwy to its north.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website the adjacent northerly hill known as Maes Glas Mawr (SH 76876 72414) was included in the main P30 list as its summit was thought to be higher than that of Clytiau Poethion (SH 76337 71799), based on a 107m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map as opposed to an upper 100m contour ring given to Clytiau Poethion.

Extract from the Ordnance Survey 1:50,000 Landranger map

Therefore, when the Dominant list was first compiled it was the hill now listed as Maes Glas Mawr that was included in the Lesser Dominant list with 36.45% dominance.

However, it was not until LIDAR became available that the details for each hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

LIDAR analysis gives Clytiau Poethion as higher than Maes Glas Mawr and this has subsequently been confirmed by a Trimble GeoXH 6000 survey, therefore the bylchau for each hill is swapped as are their classifications, resulting in a Trimble GeoXH 6000 summit height for Clytiau Poethion of 109.1m positioned at SH 76337 71799, as opposed to the 108.5m summit height for Maes Glas Mawr positioned at SH 76876 72414.  This confirms the qualifying hill’s summit position compared to where previously listed, and it comes 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.

LIDAR bwlch image for Clytiau Poethion

Therefore, the summit height produced by the Trimble GeoXH 6000 survey is 109.1m and is positioned at SH 76337 71799, this position is not given a spot height on contemporary Ordnance Survey maps and is approximately 800 metres south-westward from where the previously listed summit is positioned.

The full details for the hill are:

Group:  Carneddau

Name:  Clytiau Poethion

OS 1:50,000 map:  115

Summit Height:  109.1m (converted to OSGM15)

Summit Grid Reference (new position):  SH 76337 71799

Bwlch Height:  68.7m (LIDAR)

Bwlch Grid Reference:  SH 77496 72493 (LIDAR)

 

Drop:  40.35m (Trimble summit and LIDAR bwlch)

Dominance:  37.00% (Trimble summit and LIDAR bwlch)

For details on the summit survey of this hill

Myrddyn Phillips (April 2019)

Mapping Mountains – Hill Reclassifications – 100m Twmpau

Clytiau Poethion (SH 763 717) – 100m Twmpau addition

There has been an addition of a hill that is now listed in the 100m Twmpau, with the summit height and its location, the drop and status of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000, both conducted by Myrddyn Phillips with the latter taking place on the 10^th October 2018.

LIDAR image of Clytiau Poethion and Maes Glas Mawr

The criteria for the list that this reclassification applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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.

The name of the bounded land where the summit of this hill is situated is Clytiau Poethion, and this was derived from the Tithe map and it is the name that this hill is now listed by, and it is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and the hill is encircled by minor roads with the B5106 and the Afon Conwy (River Conwy) to its east, and has the town of Conwy to its north.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website the adjacent northerly hill known as Maes Glas Mawr (SH 76876 72414) was included in the main P30 list as its summit was thought to be higher than that of Clytiau Poethion (SH 76337 71799).

However, it was not until LIDAR became available that the details for each hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.  

Importantly LIDAR analysis gave Clytiau Poethion as higher than Maes Glas Mawr and this has subsequently been confirmed by a Trimble GeoXH 6000 survey, therefore the bylchau for each hill is swapped as are their classifications, resulting in a Trimble GeoXH 6000 summit height for Clytiau Poethion of 109.1m positioned at SH 76337 71799, and a bwlch height of 68.7m produced by LIDAR analysis and positioned at SH 77496 72493, with these values giving this hill 40.35m of drop, which is sufficient for this hill to be included in the 100m Twmpau.

 

Gathering data at the summit of Maes Glas Mawr

Gathering data at the summit of Clytiau Poethion

The full details for the hill are:

Group:  Carneddau

Name:  Clytiau Poethion

OS 1:50,000 map:  115

Summit Height:  109.1m (converted to OSGM15)

Summit Grid Reference:  SH 76337 71799

Bwlch Height:  68.7m (LIDAR)

Bwlch Grid Reference:  SH 77496 72493 (LIDAR)

Drop:  40.35m (LIDAR)

For details on the summit survey of this hill

Myrddyn Phillips (March 2019)

Mapping Mountains – Significant Name Changes – 100m Twmpau and Y Trechol – The Dominant Hills of Wales

Clytiau Poethion (SH 763 717)

There has been a Significant Name Change to a hill that is now listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height and its location, the drop and status of the hill confirmed by LIDAR analysis and its summit height subsequently confirmed by a Trimble GeoXH 6000 survey, both conducted by Myrddyn Phillips, with the latter taking place on the 10^th October 2018.

LIDAR image of Clytiau Poethion (SH 763 717)

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

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The hill is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is encircled by minor roads with the B5106 and the Afon Conwy (River Conwy) to its east, and has the town of Conwy to its north.

The hill has not previously been listed as its adjacent northerly hill of Maes Glas Mawr (SH 76876 72414) was thought to be higher, LIDAR analysis and the survey with the Trimble GeoXH 6000 proved otherwise and therefore Clytiau Poethion is now listed as the 100m Twmpau and the Lesser Dominant hill.

As the summit of this hill comprises bounded land the details for it were examined on the Tithe map.  The term Tithe map is generally given to a map of a Welsh or English parish or township and which was prepared after the 1836 Tithe Commutation Act.  This act allowed tithes to be paid in cash rather than goods.  The Tithe maps gave names of owners and occupiers of land in each parish and importantly for place-name research they also included the name of enclosed land.  This enclosed land is usually based on a field system, however not every field is given a name, but many are and especially so in Wales.

Extract from the Tithe map

The enclosed land where the summit of this hill is situated is given the number 195 on the Tithe map, this can be cross referenced against the apportionments; it is these apportionments that give the name of the owner or occupier of the land as well as the name of the land.  The land where the summit of this hill is situated is named as Clylliau [sic] Poethion in the apportionments, with the details on the Tithe map appearing in the parish of Caerhun and in the county named as Caernarvonshire [sic].

Extract from the apportionments

Therefore, the name this hill is now listed by in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales is Clytiau Poethion, and this name was derived from the Tithe map.

The full details for the hill are:

Group:  Carneddau

Name:  Clytiau Poethion

Previously Listed Name:  not previously listed 

OS 1:50,000 map:  115

Summit Height:  109.1m (converted to OSGM15)

Summit Grid Reference:  SH 76337 71799

Bwlch Height:  68.7m (LIDAR)

Bwlch Grid Reference:  SH 77496 72493 (LIDAR)

 

Drop:  40.35m (Trimble summit and LIDAR bwlch)

Dominance:  37.00% (Trimble summit and LIDAR bwlch)

For details of the summit survey of this hill

Myrddyn Phillips (March 2019)

Mapping Mountains – Trimble Surveys – Carnedd Llywelyn

10.10.18  Maes Glas Mawr (SH 768 724) and Clytiau Poethion (SH 763 717)  

Maes Glas Mawr (SH 768 724)

Having analysed these two hills with LIDAR I knew before visiting that in all likelihood the subsequent Trimble survey would confirm the summit relocation of Maes Glas Mawr to Clytiau Poethion, with the former becoming a Sub-Twmpau and the latter a new P30.  However, there were reports on the Hill Bagging website that both summits were plagued with gorse, and as I (and the Trimble) do not like gorse it was conjecture if summit data from either hill could be gathered.

LIDAR image of Maes Glas Mawr and Clytiau Poethion

As I parked on the outskirts of the small community of Tyn-y-groes the morning’s sunshine was now turning unseasonably warm with blue skies radiating down and hardly a patch of cloud in the sky.

A public footpath led north-west from the western fringes of Tyn-y-groes toward the summit of Maes Glas Mawr and once I’d done battle with a barb wired fence resulting in another battle scar, this time a bloodied finger, I plodded up toward its summit.

The summit of this hill consists of a steep north-westerly side with the upper part covered in high gorse.  Thankfully the highest point was on the edge of the gorse looking down over the steep flank of the hill, this at least gave a semblance of chance for gathering data.

Implanted in to the summit were the remains of a gnarled gorse bush and by wedging my rucksack in to its wooded lower part and placing the Trimble on top, it gave it elevation above its immediate surrounds, and a relatively secure position to balance atop for the allotted data collection.

The Trimble set-up position at the summit of Maes Glas Mawr

As it beeped away gathering its individual datum points I sat amongst the gorse on a small patch of grass and luxuriated in a restful few minutes bathed in morning sunshine.

Gathering data at the summit of Maes Glas Mawr

Once data were gathered and stored I walked the short distance down to Glyn Uchaf farm where I hoped to make place-name enquiries for the hill.  A note pinned to the door gave instructions to call at the ‘new house’ if there was no reply at the farm.  I proceeded down the track to the new house and knocked on the door, Tomi Owen answered and without a moment’s hesitation invited me in.  Within a few minutes Tomi was offering me a cup of tea, or cold drink and some shortbread.  I spent about 20 minutes with Tomi and he proved a delight to speak with, telling me that the upper field where the summit of this hill is situated is known as Maes Glas Mawr.

A nice way to spend a part of a hill walk

Tomi Owen

Having finished my drink and eaten my shortbread I thanked Tomi for his hospitality and headed down the continuation of the track to a minor road and a footpath through Craflwyn wood, this brought me down to another minor road and a walk up it to try and gain access to the field leading toward the gorse laden summit of Clytiau Poethion.

By now it was beginning to get quite warm and the thought of gorse bashing in shorts and a short sleeved top did not enthuse me, however it needed to be done and my first venture in to the prickly stuff unearthed a rather exotic looking plant.  This is the first time I’d seem such a plant on a Welsh hill, although I suspect there are many more dotted around the landscape.

An exotic looking plant on Clytiau Poethion

Deciding that the summit was not by this spot I backtracked out of the gorse and tried another spot, this again was not the summit, I backtracked and tried a different angled approach but within a few metres I again backtracked.  Fourth time lucky I thought, and this time I followed the grass at the periphery of the gorse to its high point and tried to find a relatively easy way in to the prickly stuff.

The easiest option seemed to be to head toward a prominent telegraph pole and work my way up the ridge toward its high point, I was at last making progress and using the Trimble as a hand-help device I zeroed in to the summit position.  When found it proved to be amongst a mass of very high gorse, I wondered what to do.  Not to be outdone I wondered if I could balance the Trimble on a gorse branch and gather data from this elevated position, and as said branch was positioned over what I judged to be the high point of the hill, it proved a relatively easy way to overcome the difficulty.

The Trimble set-up position at the summit of Clytiau Poethion

As the Trimble gathered ten minutes of data I sat below it, looking up toward it as it balanced precariously like a meerkat standing bolt upright on a slender elevated branch.  I wondered what the data set would be like once processed, but as I seldom carry the 2m pole this unusual surveying position would have to do.

Gathering data at the summit of Clytiau Poethion

The Trimble survived its adventure and once packed away I found an easy way out of the gorse leading me down on a public footpath toward the renovated farm house of Clytiau Poethion.  The land where the summit of this hill is situated is named on the Tithe map as a part of this farm’s land; and not surprisingly the Tithe names this land after that of the farm; Clytiau Poethion.

Looking back toward the summit of Clytiau Poethion

It was only a short walk from here following the minor road to where my car was parked.  My next objective was to visit and survey three hills and attempt to determine which is higher, this is something I’ve wanted to do ever since first listing them many a year ago; Bryn Eithin (SH 775 752), Bwlch Mawr (SH 777 755) and Cae Alen (SH 781 758).

Survey Result:

Maes Glas Mawr (significant name change)

Summit Height:  108.5m (converted to OSGM15) (confirmed as lower than Clytiau Poethion)

Summit Grid Reference:  SH 76876 72414

Bwlch Height:  87.05m (LIDAR)

Bwlch Grid Reference:  SH 76604 71933 (LIDAR)

Drop:  21.4m (Trimble summit and LIDAR bwlch) (100m Twmpau reclassified to 100m Sub-Twmpau)

Dominance:  19.76% (Trimble summit and LIDAR bwlch)

Clytiau Poethion (significant name change)

Summit Height:  109.1m (converted to OSGM15) (confirmed as higher than Maes Glas Mawr)

Summit Grid Reference:  SH 76337 71799 (summit relocation confirmed)

Bwlch Height:  68.7m (LIDAR)

Bwlch Grid Reference:  SH 77496 72493 (LIDAR)

Drop:  40.35m (Trimble summit and LIDAR bwlch) (100m Twmpau addition)

Dominance:  37.00% (Trimble summit and LIDAR bwlch)

For further details please consult the Trimble Survey Spreadsheet