Showing posts with label Pt. 505.8m (SN 785 598). Show all posts
Showing posts with label Pt. 505.8m (SN 785 598). Show all posts

Tuesday, 21 November 2023

Mapping Mountains – Significant Height Revisions – Welsh Highlands – Uchafion Cymru


Pt. 505.8m (SN 785 598) 

There has been a Significant Height Revision to a hill that is listed in the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams. 

LIDAR image of Pt. 505.8m (SN 785 598)

The criteria for the list that this height revision applies to are:

Welsh Highlands – Uchafion Cymru Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop.  This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The hill is being listed by the point (Pt. 505.8m) notation and it is adjoined to the Esgair Wen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north-west and south, and has the small community of Pontrhydfendigaid towards the north-west and the town of Tregaron towards the west. 

Extract from the Ordnance Survey series of Six-Inch maps

When the initial P10 sub list was completed in June 2020 this hill was listed with an estimated c 9m of drop, based on the 1649ft (502.6m) height that appeared on the Ordnance Survey series of Six-Inch maps and an estimated c 494m bwlch height, based on interpolation of 5m contouring that appeared on online mapping. 

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

The height that appeared on the Ordnance Survey series of Six-Inch maps was at odds with the 506m spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 78576 59903, however this spot height was not supported by contemporary contour information on large scaled Ordnance Survey maps. 

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 Pt. 505.8m (SN 785 598)

LIDAR analysis gives the highest ground on this hill as 505.8m positioned at SN 78575 59899, 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, the new listed summit height of this hill is 505.8m and this was derived from LIDAR analysis, this is 3.2m higher than the previously listed summit height which was derived from the 1649ft (502.6m) height that appeared on the Ordnance Survey series of Six-Inch maps.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Esgair Wen

Name:  Pt. 505.8m

OS 1:50,000 map:  146, 147

Summit Height (New Height):  505.8m (LIDAR)

Summit Grid Reference:  SN 78575 59899 (LIDAR)

Bwlch Height:  492.4m (LIDAR)

Bwlch Grid Reference:  SN 78513 60070 (LIDAR)   

Drop:  13.5m (LIDAR) 

 

Myrddyn Phillips and Aled Williams (November 2023)

  

Thursday, 16 November 2023

Mapping Mountains – Hill Reclassifications – Welsh Highlands – Uchafion Cymru


Pt. 505.8m (SN 785 598) – Welsh Highland Sub addition 

There has been an addition to the listing of the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams. 

LIDAR image of Pt. 505.8m (SN 785 598)

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

Welsh Highlands – Uchafion Cymru Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop.  This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The hill is being listed by the point (Pt. 505.8m) notation and it is adjoined to the Esgair Wen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north-west and south, and has the small community of Pontrhydfendigaid towards the north-west and the town of Tregaron towards the west. 

Extract from the Ordnance Survey series of Six-Inch maps

When the initial P10 sub list was completed in June 2020 this hill was listed with an estimated c 9m of drop, based on the 1649ft (502.6m) height that appeared on the Ordnance Survey series of Six-Inch maps and an estimated c 494m bwlch height, based on interpolation of 5m contouring that appeared on online mapping. 

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

The height that appeared on the Ordnance Survey series of Six-Inch maps was at odds with the 506m spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 78576 59903, however this spot height was not supported by contemporary contour information on large scaled Ordnance Survey maps. 

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 addition of this hill to Welsh Highland Sub status is due to LIDAR analysis, resulting in a 505.8m summit height and a 492.4m bwlch height, with these values giving this hill 13.5m of drop, which is sufficient for it to be classified as a Welsh Highland Sub. 

 

The full details for the hill are: 

Group:  Esgair Wen

Name:  Pt. 505.8m

OS 1:50,000 map:  146, 147

Summit Height:  505.8m (LIDAR)

Summit Grid Reference:  SN 78575 59899 (LIDAR)

Bwlch Height:  492.4m (LIDAR)

Bwlch Grid Reference:  SN 78513 60070 (LIDAR)   

Drop:  13.5m (LIDAR) 

 

For the additions, deletions and reclassifications to the Welsh Highlands – Uchafion Cymru reported on Mapping Mountains please consult the following Change Registers:

 

Welsh Highland P15s

 

Welsh Highland Subs

 

Aled Williams and Myrddyn Phillips (November 2023)

  

Sunday, 15 October 2023

Mapping Mountains – Trimble Surveys – Esgair Wen


09.09.23  Pt. 505.8m (SN 785 598) and Esgair Hirnant (SN 792 594) 

Esgair Hirnant (SN 792 594)

It was back to the Tywi Forest today, to visit Esgair Hirnant and an adjacent Welsh Highland Sub, the higher prominence hill is one of four remaining for my completion of the Welsh Highlands – Uchafion Cymru list; however I also have to re-visit Mynydd Trawsnant as LIDAR has relocated its summit, so although there are four hills remaining, there are five walks for a completion!

Over recent months the expanse of the Tywi Forest has been interesting to explore.  I did a big circular walk around many of its 500m P15s in 2009 when one forest break led to another and miraculously progress was made from hill to hill.  Since then the remaining hills have been visited as single forays which have given days of relative relaxation with only an occasional summit where wind-blown trees resulted in producing an obstacle course.

When the list that is now known as the Welsh Highlands – Uchafion Cymru was first compiled there were a number of hills that I examined on the map that did not overexcite.  These were mainly bog-bound or covered in conifer plantation.  Three hills stood out, and all could be combined, if feeling adventurous.  These are Esgair Gerwyn (SN 788 586), Esgair Hirnant (SN 792 594) and Esgair Saeson (SN 795 603).  The latter will soon be officially deleted from the Welsh Highlands – Uchafion Cymru list as its 500m map height comes to 498.4m after LIDAR analysis.  Therefore, this just left just two of these hills.  Along with Aled I visited Esgair Gerwyn in July of this year when we drove up a forest track and parked close to its summit.  We now planned to use the same forest track and drive beyond Esgair Gerwyn and park close to a forest ride to the west of Esgair Hirnant.  This would allow relatively easy access to its summit, as long as there were no wind-blown trees scattered across the forest breaks and its high point.  Between our planned parking place and the summit of Esgair Hirnant was a Welsh Highland Sub that Aled wanted to visit.  These two hills would be my objective for the day, however Aled wanted to visit a further five hills, three being classed as Deweys and another two as Welsh Highland Subs, and if possible to ease the going for Aled I would drive between each.  We needed good weather to do this and for the barrier at the entrance to the forest track to be open, and with a forecast for dry and warm conditions it was an ideal day to visit.

I was driving on the mountain road through Cwm Tywi before 8.30am, having picked Aled up in Caersŵs.  This road is a delight to drive on and in its full length is one of the wildest in Wales.  We were soon approaching the start of the forest track which would lead toward our chosen hills and thankfully the barrier was open giving us access up in to the forest.  We soon passed were we had parked for Esgair Gerwyn and continued heading westward, stopping once to take photos of our hill in the morning sunlight. 

On the forest tracks in the Tywi Forest

The track then lost height, crossed a stream and headed northward, gaining height as it did so.  From this direction there are two forest breaks that head east toward the summit of Esgair Hirnant, we parked close to the northly of these, but on Aled’s recommendation from aerial images we walked back down the forest track to the southerly of the two forest breaks.

Entering the forest

We entered the forest on what proved an extremely good and wide forest ride.  Underfoot conditions were generally good, with the forest ride having copious amounts of summer Elenydd grass in evidence.  This can be torturous on the hill as it is tough and in the summer months can be so thick that any sheep path is soon smothered from view.  As occasional boggy patch showed itself through the grass, but in general the going proved relatively easy. 

Heading toward the summit of the Welsh Highland Sub

As we walked eastward the first sub of the day was to our left, and therefore we soon left the comfort of the forest ride and headed in to the trees.  Thankfully at the moment these are mature and therefore gave easy access through them.  Nearing the summit of the sub a few wind-blown trees barred direct progress but we were soon standing on the summit area and with the aid of the Trimble used as a hand-held GPS we zeroed in to the LIDAR co-ordinates Aled had produced.  A few summit photos were taken before we headed back down through the trees toward the forest break. 

At the summit of the sub

Heading further eastward we soon came upon a crossroads where a 487m spot height appears on the contemporary Ordnance Survey 1:25,000 Explorer map.  From here the summit of Esgair Hirnant can be approached on forest breaks from its north or south.  The southerly approach is slightly shorter with a little height lost toward its end when another forest break heads for the summit, the northerly approach contours the land without losing height and is slightly longer, we opted for the southerly approach. 

The cross roads of forest breaks where the 487m spot height appears on the Ordnance Survey 1:25,000 Explorer map

By now the conditions in the forest were starting to become humid, thankfully we were rarely in direct sunlight, with the shade at least giving some comfort from what was an increasingly warm day ahead.  We soon passed another crossroads of forest breaks, if turning left this would connect up with the break on the northerly side of the summit.  Continuing we soon came to the forest break on our left that would take us to the high point of Esgair Hirnant.  Considering how horrendous this approach could have been, it thankfully proved relatively easy. 

Approaching the summit of Esgair Hirnant

The forest break took us up to the high point of Esgair Hirnant where with the aid of the Trimble we zeroed in to the LIDAR co-ordinates for the summit.  We remained on top for a few minutes, taking photos and in my case; regaining my breath.  The tree branches were festooned in mosses, all hanging forlornly in the shade with blue sky piercing the canopy above. 

At the summit of Esgair Hirnant

As we reversed our inward route I followed Aled as he kept parallel to the break but inside the forest.  This at least shielded us from the sunlight which was now illuminating patches of the forest ride. 

Heading back out of the forest

Emerging out of the trees it was only a slow plod back up the forest track to where the car was parked.  For me my days’ walking was over, but for Aled he still wanted to visit five more hills.  This necessitated driving between each hill and dropping Aled off and watching him disappear in to the trees, emerging again with one or two horror stories of thick undergrowth and almost impenetrable summits.

The last hill Aled wanted to visit was Cefn y Cnwc (SN 773 588), we hoped to park immediately under it to its west and then continue down the track and exit close to where a red kiosk used to stand and back on to the paved minor road.  However, as we approached on the track to where a cattle grid and mast are positioned a locked barrier across the forest track barred further progress.  We debated various options until Aled said he’d walk to the hill from here, this meant losing height on the track to avoid a particularly gruesome looking bog, and for the inward route to be reversed after visiting its summit, regaining height on the track as he did so. 

The locked barrier that halted the continued drive on the forest tracks

As Aled headed off for his last hill of the day I turned the car around, opened the doors to let in fresh air and walked beyond the barrier around the corner of the track to take photos of the hill and watch Aled walk up it.  I then headed back to the car and sat on my camping chair in the afternoon sun reading, until Aled appeared having visited the hill.  He’d done well today as one or two summits were tough. 

Cefn y Cnwc (SN 773 588)

All that remained was the drive out on the track back down to our entrance point where the barrier was thankfully still open.  Just three Welsh Highland P15s to visit. 

 

Survey Result:

 

Pt. 505.8m                                

Summit Height:  505.8m (LIDAR) (significant height revision)

Summit Grid Reference:  SN 78575 59899 (LIDAR)

Bwlch Height:  492.4m (LIDAR)

Bwlch Grid Reference:  SN 78513 60070 (LIDAR)

Drop:  13.5m (LIDAR) (Welsh Highland Sub addition)

Dominance:  2.66% (LIDAR)

                                       

 

Esgair Hirnant                          

Summit Height:  505.1m (LIDAR)

Summit Grid Reference:  SN 79200 59463 (LIDAR)

Bwlch Height:  487.3m (LIDAR)

Bwlch Grid Reference:  SN 78820 59802 (LIDAR)

Drop:  17.7m (LIDAR)

Dominance:  3.51% (LIDAR)

 

 

For further details please consult the Trimble Survey Spreadsheet