Mapping Mountains – Significant Height Revisions – Yr Uchafion and 800m Twmpau

Carnedd y Filiast (SH 620 627)

There has been a Significant Height Revision to a hill that appears in the listings of Yr Uchafion and 800m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams which took place on the 6^th July 2019.

Carnedd y Filast (SH 620 627)

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

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to the list appearing on Mapping Mountains on the 4^th November 2015 and an update relating to the list appearing on Mapping Mountains on the 19^th June 2019.

800m Twmpau - Welsh hills at or above 800m and below 900m in height with 30m minimum drop, with an accompanying sub list entitled the 800m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 800m and below 900m 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 list is authored by Myrddyn Phillips and the details to it were published on Mapping Mountains on the 15^th March 2015.

The name of the hill is Carnedd y Filiast and it is adjoined to the Glyderau 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 Afon Ogwen and the A5 road to its north-east and Llyn Padarn, Llyn Peris and the A4086 road towards its south-west, and has the town of Bethesda towards the north and the village of Llanberis towards the west south-west.

Prior to the Trimble GeoXH 6000 survey the height of the hill was listed as 821m which is based on the summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

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

The summit height produced by the Trimble GeoXH 6000 is 823.6m, this is not a dramatic height revision when compared to some survey results, 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 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. 

The Trimble GeoXH 6000 gathering data at the summit of Carnedd y Filiast

Therefore, this hill’s new summit height as surveyed with the Trimble GeoXH 6000 is 823.6m, this is positioned at SH 62040 62733 and is 2.6m higher than its previously listed height of 821m which appears as a spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Glyderau

Name:  Carnedd y Filiast

OS 1:50,000 map:  115

Summit Height (New Height):  823.6m (converted to OSGM15)

Summit Grid Reference:  SH 62040 62733

Bwlch Height:  744.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 61995 61535

Drop:  79.1m

For details on the survey of this hill

Myrddyn Phillips and Aled Williams (October 2019)

Mapping Mountains – Significant Height Revisions – Yr Uchafion and 600m Twmpau

Pen y Boncyn Trefeilw (SH 962 283)

There has been a Significant Height Revision to a hill that is listed in the Yr Uchafion and 600m Twmpau, with the summit height and drop of the hill being confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips on the 16^th August 2018.  The summit of this hill was subsequently surveyed by Alan Dawson using a Leica RX1250 on the 24th November 2018, and it is this result that is given in the details for the hill at the end of this article.

Pen y Boncyn Trefeilw (SH 962 283)

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

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to this list appearing on Mapping Mountains on the 4^th November 2015.

600m Twmpau – Welsh hills at or above 600m and below 700m in height that have 30m minimum drop, with an accompanying sub category entitled the 600m Sub-Twmpau consisting of all Welsh hills at or above 600m and below 700m in height that have 20m or more and below 30m of drop.  With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips.

The name of the hill is Pen y Boncyn Trefeilw, and it is adjoined to the Y Berwyn range of hills, which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned to the north of Llyn Efyrnwy (Lake Vyrnwy) and has the town of Y Bala towards the north north-west.

As the summit of the hill is not a part of designated open access land permission to visit should be sought, however the upper part of this hill is encircled by open access land and the summit of the hill is only a few metres from the boundary fence between this land and the grazing field where it is situated.  Therefore common sense should prevail for those who want to visit.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with a 646m summit height, which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

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

The summit height produced by The Trimble GeoXH 6000 survey is 644.0m (643.953m to three decimal places) (converted to OSGM15), this is not a substantial 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 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.  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 revisions.

The Trimble GeoXH 6000 gathering data at the summit of Pen y Boncyn Trefeilw

Therefore, this hill’s new summit height is 644.0m (converted to OSGM15) and this was produced by surveying with the Trimble GeoXH 6000, this is 2.0m lower than its previously listed height of 646m which appears as a spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  However, this new height is in accordance with the 5m contouring on OS Maps.

The above details have now been superseded by the Leica RX1250 survey conducted by Alan Dawson, and it is this summit result that is given below. 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Y Berwyn

Name:  Pen y Boncyn Trefeilw

OS 1:50,000 map:  125

Summit Height (New height):  644.2m (converted to OSGM15)

Summit Grid Reference:  SH 96250 28328

  

Bwlch Height:  588.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 97406 27854

Drop:  55.8m (Leica RX1250 summit and Trimble GeoXH 6000 bwlch)

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips and Aled Williams (January 2019)

Mapping Mountains – Significant Height Revisions – Yr Uchafion, 700m Twmpau and Y Pellennig – The Remotest Hills of Wales

Fan y Big (SO 036 206)

There has been a Significant Height Revision to a hill that appears in the following lists; Yr Uchafion, 700m Twmpau and Y Pellennig – The Remotest Hills of Wales, and which was initiated by LIDAR analysis conducted by Aled Williams followed by a survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter conducted over two days on the 30^th June 2018 and the 21^st August 2018 in clear conditions turning to mist on the first survey and misty conditions clearing on the second survey.

LIDAR image of Fan y Big

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

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to the list appearing on Mapping Mountains on the 4^th November 2015.

700m Twmpau - Welsh hills at or above 700m and below 800m in height with 30m minimum drop, with an accompanying sub list entitled the 700m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 700m and below 800m 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 list is authored by Myrddyn Phillips.

Y Pellennig –The Remotest Hills of Wales - Welsh hills whose summit is at least 2.5km from the nearest paved public road and the hill has a minimum 15m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available as a downloadable e-booklet or print-booklet version on Mapping Mountains Publications with the up-to-date master list available on Mapping Mountains in Google Doc format.

The name of the hill is Fan y Big and it is placed in the central part of the main ridge that forms the Bannau Brycheiniog (Brecon Beacons) group of hills, which are situated in the South Wales Region (Region C, Sub-Region C2), and it is positioned between the towns of Aberhonddu (Brecon) to its north and Merthyr Tudful to its south.

The hill can be accessed from public footpaths originating from its north and from its south; or it can be combined as a longer expedition taking in the main Bannau Brycheiniog ridge either from its west or from its east.

Prior to LIDAR analysis and the subsequent survey with the Trimble GeoXH 6000 the height of the hill was listed as 719m based on the summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:125,000 Explorer map

The summit of this hill was surveyed three times over two days, each 53 days apart resulting in the following:

1^st survey 30.06.18:  716.800m

2^nd survey 30.06.18:  716.676m

3^rd survey 21.08.18:  716.754m

Average of three summit surveys:  716.746m

Therefore, the average of three summit surveys produced by the Trimble GeoXH 6000 is 716.7m (converted to OSGM15), this is not a dramatic height revision when compared to some survey results, 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 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.  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 revisions.

Therefore, this hill’s new summit height as surveyed with the Trimble GeoXH 6000 is 716.7m (converted to OSGM15) which is 2.3m lower than its previously listed height of 719m which appears on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The Trimble GeoXH 6000 gathering data at the summit of Fan y Big which resulted in this hill's significant height revision

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Bannau Brycheiniog

Summit Height (New height):  716.7m (converted to OSGM15)

Name:  Fan y Big

OS 1:50,000 map:  16o

Summit Grid Reference:  SO 03652 20658

  

Drop:  28.5m (converted to OSGM15)

For details on the 1st survey that significantly revised the summit height of this hill

For details on the 2nd survey that significantly revised the summit height of this hill

Myrddyn Phillips and Aled Williams (November 2018)

Mapping Mountains – Significant Height Revisions – Yr Uchafion and 500m Twmpau

Banc y Foel (SN 725 186)

There has been a Significant Height Revision to a hill that appears in the Yr Uchafion and 500m Twmpau lists, and which was initiated by a survey with the Trimble GeoXH 6000 which was conducted on the 6^th May 2018 in good, clear conditions with hardly a breath of breeze.

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

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to the list appearing on Mapping Mountains on the 4^th November 2015.

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips.

The name of the hill is Banc y Foel and it is adjoined to the Mynydd Du range of hills, which are positioned in the western part of South Wales (Region C, Sub-Region C1).  The hill is positioned with the A 4069 road to its east, and has the village of Llangadog towards the north and Brynaman towards the south.

Banc y Foel (SN 725 186)

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was estimated as c 536m based on a relatively large 530m uppermost contour ring on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

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

The summit height produced by The Trimble GeoXH 6000 survey is 531.6m (converted to OSGM15), this is a substantial height revision when compared to some revised heights, and 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 by LIDAR analysis, 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 analysis of LIDAR.  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 revisions.

Therefore, this hill’s new summit height is 531.6m (converted to OSGM15) and this was produced by surveying with the Trimble GeoXH 6000, this is 4.4m lower than its previously listed height of c 536m which was based on interpolation of the hill’s uppermost 530m ring contour on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Mynydd Du

Name:  Banc y Foel

OS 1:50,000 map:  160

Summit Grid Reference:  SN 72536 18670 

 

Summit Height (New height):  531.6m (converted to OSGM15)

Drop:  38.9m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Banc y Foel (SN 725 186) which resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips and Aled Williams (July 2018)

Mapping Mountains – Significant Height Revisions – Yr Uchafion and 700m Twmpau

Twyn Llech (SO 255 353)

There has been a Significant Height Revision to a hill that appears in the Yr Uchafion and 700m Twmpau lists, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that resulted in this height revision being conducted on the 28^th September 2017 in good, clear conditions with just a breath of breeze.

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

Yr Uchafion – All Welsh hills at and above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to the list appearing on Mapping Mountains on the 4^th November 2015.

700m Twmpau – All Welsh hills at and above 700m and below 800m in height that have 30m minimum drop, with the word Twmpau being an acronym standing for ‘thirty welsh metre prominences and upward’.  The list is authored by Myrddyn Phillips.

The name of the hill is Twyn Llech and it is a part of the Mynyddoedd Duon (Black Mountains) range, which is an extensive group of hills in the south-eastern part of South Wales, and it is situated above and between the upper part of the Olchon Valley to its south-east and the Dyffryn Ewias (Vale of Ewyas) to its south.  The hill is also situated between the small communities of Craswall towards its east and Capel-y-ffin towards its south, and the hill can be accessed from a car park just below the high point of Bwlch yr Efengyl (Gospel Pass) via the summit of Hay Bluff, or it can be approached from the south-east via paths leading to its southerly ridge from either the Olchon Valley and the Dyffryn Ewias (Vale of Ewyas).

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 706m based on the summit spot height which is positioned at approximately SO 25545 35372 (taken by using a ruler) on the Harvey 1:40,000 Offa’s Dyke South map.  Whilst Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps give a summit spot height of 703m positioned at SO 25586 35010.

The Harvey maps 706m summit spot height

The Ordnance Survey 703m summit spot height

Two points were surveyed for summit position using the Trimble GeoXH 6000, one on the southerly point where the Ordnance Survey give their 703m spot height and one on the northerly point where Harvey maps give their 706m spot height.  The summit area of this hill has two rises which complement these spot height positions and which have a slight dip in between.

The results produced by the Trimble GeoXH 6000 appear below:

Northerly high point:  703.639m (converted to OSGM15) at SO 25520 35383

Southerly high point:  702.721m (converted to OSGM15) at SO 25572 35032

The above result 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 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, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  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 revisions.

As the Harvey summit position was the one used for listing, it is the 706m spot height that this Significant Height Revisions post applies to.

The summit of this hill consists of tussock grass close to the main and now well maintained paved path that crosses this hill on a south – north direction, and therefore this hill’s new summit height as surveyed with the Trimble GeoXH 6000 is 703. 6m (converted to OSGM15) which is 2.4m lower than its previously listed height of 706m which appears on the Harvey 1:40,000 Offa’s Dyke South map.

ills of Wales, and are reproduced below@

The full details for the hill are:

Cardinal Hill:  Twyn Llech

Summit Height (New height):  703.6m (converted to OSGM15)

Name:  Twyn Llech

OS 1:50,000 map:  161

Summit Grid Reference:  SO 25520 35383 

 

Drop:  154.5m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Twyn Llech (SO 255 353) which resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips and Aled Williams (November 2017)