Saturday, 31 July 2021

Mapping Mountains – Significant Height Revisions – 30-99m Twmpau


Pen y Graig Wen (SH 446 879) 

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pen y Graig Wen (SH 446 879)

The criteria for the list that this height revision 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. 

The 30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Pen y Graig Wen and this was derived from the Tithe map 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 is positioned with the coast to its east, minor roads to its north, south and east and the B5111 road to its west, and has the village of Rhos-y-bol towards the west north-west. 

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 24m of drop, based on an estimated c 92m summit height positioned at SH 44769 87804 and an estimated c 68m bwlch height, with both heights based on interpolation of 5m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

However, it was not until LIDAR became available that the details for this 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. 

The summit height produced by LIDAR analysis is 94.3m, and this comes 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 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 94.3m and this was derived from LIDAR analysis, this is 2.3m higher than the previous listed summit height of c 92m which was based on interpolation of the uppermost 90m contour that appears on the Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Ynys Môn 

Name:  Pen y Graig Wen 

OS 1:50,000 map:  114

Summit Height (New Height):  94.3m (LIDAR) 

Summit Grid Reference:  SH 44637 87986 (LIDAR) 

Bwlch Height:  68.2m (LIDAR) 

Bwlch Grid Reference:  SH 45162 88579 (LIDAR) 

Drop:  26.1m (LIDAR) 

 

Myrddyn Phillips (July 2021)

 

 

 

 

 

 

  

Mapping Mountains – Hill Reclassifications – 200m Twmpau

 

Pen yr Allt (SH 842 025) – 200m Sub-Twmpau addition

There has been confirmation of an addition to the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Pen yr Allt (SH 842 025)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Pen yr Allt and it is adjoined to the Pumlumon group of hills which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is encircled by minor roads with the A470 road farther to its north-east, and has the village of Comins-coch towards the north-east. 

When the original 200m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 25m of drop, based on the 267m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 242m bwlch height based on interpolation of 10m contouring between 240m – 250m. 

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

However, it was not until LIDAR became available that the details for this 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 summit image of Pen yr Allt (SH 842 025)

Currently LIDAR only covers the summit area of this hill and as the summit and bwlch have now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes. 

The Trimble GeoXH 6000 gathering data at the bwlch of Pen yr Allt

The Trimble GeoXH 6000 gathering data at the summit of Pen yr Allt

Therefore, the confirmation of the addition of this hill to 200m Sub-Twmpau status is due to LIDAR summit analysis and a subsequent Trimble GeoXH 6000 survey, resulting in a 266.6m summit height and a 241.9m bwlch height, with these values giving this hill 24.7m of drop, which is sufficient for it to be classified as a 200m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Pumlumon 

Name:  Pen yr Allt 

OS 1:50,000 map:  135, 136

Summit Height:  266.6m (converted to OSGM15) 

Summit Grid Reference:  SH 84232 02576 

Bwlch Height:  241.9m (converted to OSGM15) 

Bwlch Grid Reference:  SH 84202 02341 

Drop:  24.7m 

 

Myrddyn Phillips (July 2021)

 

 

 

Friday, 30 July 2021

Mapping Mountains – Hill Reclassifications – The Welsh P15s


Nant y Frân (SH 389 923) – Welsh P15 reclassified to Welsh Sub-P15 

There has been a reclassification to the list of The Welsh P15s, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Nant y Frân (SH 389 923)

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

The Welsh P15s – Welsh hills with 15m minimum drop, irrespective of their height, with an accompanying sub list entitled the Welsh Sub-P15s, with the criteria for this sub category being all Welsh hills with 14m or more and below 15m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list appearing on Mapping Mountains on the 10th May 2019. 

The Welsh P15s by Myrddyn Phillips

The name the hill is listed by is Nant y Frân and this was derived from the Tithe map 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 is positioned with the coast and the A5025 road to its north, minor roads to its west, south and east, and has the village of Cemaes towards the west north-west. 

When the listing that became known as The Welsh P15s was being compiled, this hill was included in the main P15 list with 15m of drop, based on the 49m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 34m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

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

However, it was not until LIDAR became available that the details for this 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. 

Therefore, the reclassification of this hill to Welsh Sub-P15 status is due to LIDAR analysis, resulting in a 49.4m summit height and a 34.7m bwlch height, with these values giving this hill 14.7m of drop, which is insufficient for it to be included in the main list of The Welsh P15s. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Nant y Frân 

OS 1:50,000 map:  114

Summit Height:  49.4m (LIDAR)                                                           

Summit Grid Reference:  SH 38928 92356 (LIDAR) 

Bwlch Height:  34.7m (LIDAR) 

Bwlch Grid Reference:  SH 38859 92572 (LIDAR) 

Drop:  14.7m (LIDAR) 

 

Myrddyn Phillips (July 2021)

  

Mapping Mountains – Trimble Surveys – Fforest Glud

 

01.06.21  Nyth Grug (SO 170 606) and Mynd (SO 181 592) 

Nyth Grug (SO 170 606)

These two hills are positioned to the south of Great Rhos and if so desired can be combined with their higher neighbour.  However, as the summit of Great Rhos was Trimbled five days ago it was just Nyth Grug and Mynd that were on the day’s surveying agenda, and as our planned route took us over the bwlch of Crin Fynydd I hoped to also gather data from this point if the near conifers permitted. 

I was out with Linda today, my old lockdown, keep local walking buddy.  My memories of walking with Linda consisted of ear warmers, balaclavas, wellies and full winter gear visiting the delights of Yr Allt and Y Golfa and its adjacent hills.  Today was an utter contrast to those winter walks as summer had arrived giving warm temperatures on the hills. 

We were walking on the forested path beside the Water-breaks-its-neck waterfall by 9.00am, following dappled light up beneath the canopy of blues and greens.  The path led over a footbridge at the top of the waterfall and then continued downward, we left it at this point and joined a narrower path that led to a public footpath close to Warren House. 

Heading up the path leading to the top of Water-breaks-its-neck

Conditions were warm on this section of the walk and especially so as we headed beside the near conifer plantation up a field where two horses stood in the morning sunshine; one on our path bolt still, the other inquisitively roaming over to investigate the two new arrivals.  Beyond the field we entered forestry. 

Linda emerges out of the wood with Mynd in the background

The path through the forest was a delight and gave shade to the morning’s proceedings.  We stopped at the bwlch of Crin Fynydd, with its summit immersed in conifers just to our south.  It was pointless trying to gather Trimble data from its summit, but I hoped bwlch data could be gathered. 

On the path leading to the bwlch of Crin Fynydd

Whilst I assessed the lay of land Linda chose a spot and bedded down in the sun, she’d worked a 17 hour shift two days ago and deserved a good rest whilst on the hill.  We spent about 30 minutes at this bwlch, I positioned the Trimble facing in three different directions, but every time the 0.1m accuracy level before data should be logged was not attained, and therefore I eventually closed it down without any data having been collected. 

A well earned rest after a 17-hour shift

The bwlch of Crin Fynydd

Our route continued, now on the periphery of the forestry following a good track up valley with the stream feeding the waterfall down on our left.  We left the main track and followed a narrower path that exited the last of the conifers and gained open hillside.  From here to the bwlch of Nyth Grug was beautiful with open hill, few fences, blue sky, roaming sheep, circling Red Kites, a cooling breeze and not another person in sight. 

At the bwlch Linda again lay in the sun without a seeming care in the world.  The critical point of the bwlch was relatively easy to pinpoint and soon the Trimble was set up gathering its allotted data. 

Gathering data at the bwlch of Nyth Grug

Ahead of us lay the greened grazing slopes of Nyth Grug; our high point of the day.  These we followed ever upward, joining the fence that follows the broad ridge until we spotted the trig pillar and then made a direct beeline toward it. 

Having chosen the spot for Trimble placement and set the equipment to gather data I sat with Linda beside a fence looking down to a single wind turbine lazing in the sun.  It was good to be here, the conditions on the lower parts of the hills were proving warm, but on the tops a breeze blew which helped, otherwise the whole day may have been uncomfortably hot. 

Gathering data at the summit of Nyth Grug

Once the allotted data were gathered and stored we headed down the southerly ridge of Nyth Grug helping two lambs on the way, one that had got itself wedged behind a gate and the other whose head was stuck through a part of a wired fence.  I grabbed each by their fleeced coat and lifted them free and watched them shoot off to their mothers, the first jumping in the air as it did so. 

Trapped behind a gate without the knowledge of a reverse gear

The connecting bwlch between Nyth Grug and Mynd was positioned just beyond a ploughed field in another patch of greened grazing land.  Having followed the remnants of the small stream up from the east I positioned the Trimble atop my rucksack, measured and noted the offset between its internal antenna and the ground at its base and sat on the near bank as it quietly beeped away gathering its all-important data. 

Heading toward the connecting bwlch with Mynd

Gathering data at the bwlch of Mynd

Leaving the bwlch we headed uphill toward a track leading to a gate before veering left and aiming for the higher ground, soon we were on the summit of Mynd.  This summit had been LIDARed, therefore the ten figure grid reference led me toward its high point.  As the Trimble gathered data I sat with Linda chatting away with a bag of crisps in hand.

Gathering data at the summit of Mynd

Our route down led toward a descending fence line that connected with a path beside the southerly corner of the conifer plantation that spreads itself northward up valley.  We were now just a steep field away from the car. 

Before heading to Maesyfed (New Radnor) to visit its old castle, I drove the short distance on the continuation of the rough track that leads toward the visitor car park for the Water-breaks-its-neck waterfall.  Having parked we walked downhill to the stream and then followed a good path beside it to the base of the waterfall. 

Water-breaks-its-neck

I’d only been here once before, many years ago.  Then the waterfall was somewhat of a disappointment as the water was no more than a trickle.  Today it was much more impressive.  It wasn’t roaring down the cliff, but it was beautiful with the greened vegetation of ferns and mosses adding succulent colour to the scene.

 

Survey Result:

 

Nyth Grug  

Summit Height:  538.3m (converted to OSGM15)

Summit Grid Reference:  SO 17050 60690

Bwlch Height:  449.0m (converted to OSGM15)

Bwlch Grid Reference:  SO 17391 61800

Drop:  89.3m

Dominance:  16.59%


 

 

Mynd  

Summit Height:  478.7m (converted to OSGM15)

Summit Grid Reference:  SO 18111 59264

Bwlch Height:  410.3m (converted to OSGM15)

Bwlch Grid Reference:  SO 17772 59659

Drop:  68.4m

Dominance:  14.28%


 

 

For further details please consult the Trimble Survey Spreadsheet

 

Thursday, 29 July 2021

Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

 

Pen y Graig Wen (SH 446 879) – 30-99m Sub-Twmpau addition

There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pen y Graig Wen (SH 446 879)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 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. 

The 30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Pen y Graig Wen and this was derived from the Tithe map 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 is positioned with the coast to its east, minor roads to its north, south and east and the B5111 road to its west, and has the village of Rhos-y-bol towards the west north-west. 

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 24m of drop, based on an estimated c 92m summit height and an estimated c 68m bwlch height, with both heights based on interpolation of 5m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

However, it was not until LIDAR became available that the details for this 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. 

Therefore, the confirmation of the addition of this hill to 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 94.3m summit height and a 68.2m bwlch height, with these values giving this hill 26.1m of drop, which is sufficient for it to be classified as a 30-99m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Pen y Graig Wen 

OS 1:50,000 map:  114

Summit Height:  94.3m (LIDAR) 

Summit Grid Reference:  SH 44637 87986 (LIDAR) 

Bwlch Height:  68.2m (LIDAR) 

Bwlch Grid Reference:  SH 45162 88579 (LIDAR) 

Drop:  26.1m (LIDAR) 

 

Myrddyn Phillips (July 2021)