Mapping Mountains – Significant Height Revisions – Y Pedwarau

Fuches (SN 866 836)

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau, with the summit height, drop and status of the hill confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

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

Y Pedwarau – Welsh hills at or above 400m and below 500m in height that have a minimum 30m of drop, whilst the criteria for 400m Sub-Pedwar status are all Welsh hills at or above 400m and below 500m in height that have 20m or more3 and below 30m of drop.

The name of the hill is Fuches and it is adjoined to the Pumlumon range with its Cardinal Hill being Pumlumon Fawr (SN 789 869) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B2).  The hill is situated between the stream valleys of the Afon Hafren (River Severn) to the north-east and the Afon Gwy (River Wye) to the south, and has the small community of Llangurig towards the south-east. 

Although the hill is a part of designated open access land it is also immersed in conifer plantation.  However, the summit of the hill is easily reached via a wide path now used by trail riders that follows the summit ridge in a north-east to south-west direction, and this can be accessed from a forest track to the north-east of the summit.

When interpolated summit heights were added to the original Welsh P30 lists that were published on Geoff Crowder’s v-g.me website this hill was listed with an estimated c 453m summit height based on the area of its uppermost 450m contour ring on contemporary Ordnance Survey maps, this was only revised through LIDAR analysis which resulted in a summit height of 446.7m.  However, the LIDAR height was queried as the whole hill is immersed in conifer plantation and this has become known to compromise the accuracy of some LIDAR values, and as the LIDAR value also affected this hill’s status, it was decided to survey the hill with the Trimble GeoXH 6000.  

The summit height produced by the Trimble GeoXH 6000 survey is 449.3m (converted to OSGM15), this is not a dramatic height revision when considering its uppermost contour ring on contemporary Ordnance Survey maps, 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 is 449.3m (converted to OSGM15) and this was produced by a Trimble GeoXH 6000 survey, this is 3.7m lower than its original estimated height of c 453m and 2.6m higher than the height produced by LIDAR analysis.

The full details for the hill are:

Group:  Pumlumon

Name:  Fuches

OS 1:50,000 map:  135, 136

Summit Height (New Height):  449.3m (converted to OSGM15)

Summit Grid Reference:  SN 86623 83656

   

Drop:  30.2m (converted to OSGM15)

 

The Trimble set-up position at the summit of Fuches 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 (September 2018)

Mapping Mountains – Significant Height Revisions – Y Pedwarau

Twyn y Waun (SO 085 065) 

There has been a Significant Height Revision to a summit of a hill that is now listed in the Y Pedwarau, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that confirmed this height revision being conducted on the 1^st December 2017.

The criteria for the list this height revision affects are:

Y Pedwarau – All Welsh hills at and above 400m and below 500m in height that have 30m minimum drop.  Whilst the criteria for 400m Sub-Pedwar status are all Welsh hills at and above 400m and below 500m in height that have 20m or more and below 30m of drop.

The name of the hill is Twyn y Waun and this hill is the result of mine spoil from the Ffos-y-fran opencast mine, as a result it is considered a man-made hill.  It is situated in the Y Cymoedd – dwyreiniol range of hills which are in the central part of South Wales (Region C, Sub-Region C2), and it is positioned between the town of Merthyr Tudful (Merthyr Tydfil) to its west and Rhymni (Rhymney) to its east.

As this man-made hill is a part of a working mine permission to visit should be sought, for those wishing to do so a public footpath leaves the convenience of a near minor road to the north north-east of the hill.

Prior to the survey with the Trimble GeoXH 6000 this man-made hill was not classified although it had been noted; most recently by Rob Woodall who reported its approximate height and prominence.  This hill possesses no ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps with the continuation of contours from the unmined land to the east of the hill being between 400m – 410m high compared to where the summit of this man-made hill is now situated. 

The resulting survey with the Trimble GeoXH 6000 produced a summit height of 460.5m (converted to OSGM15) and a bwlch height of 419.5m (converted to OSGM15), with these values giving this hill 41.0m of drop, with the summit height being a dramatic increase in height compared to the continuation of map contours from the unmined land to the east and therefore it 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.

Therefore, the new height for this man-made hill 460.5m (converted to OSGM15), and as no contours exist for this hill on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps this is a dramatic 50.5m increase in height compared to the continuation of the 410m contour from the unmined land to the east of this hill.

The full details for the hill are:

Cardinal Hill:  Twyn y Waun

Summit Height (New Height):  460.5m (converted to OSGM15)

Name:  Twyn y Waun

OS 1:50,000 map:  160

Summit Grid Reference:  SO 08549 06591

Drop:  41.0m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Twyn y Waun (SO 085 065) which resulted in this hill's significant height revision

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

Myrddyn Phillips and Aled Williams (January 2018)

Mapping Mountains – Significant Height Revisions – Y Pedwarau

Pawl Hir (SO 101 595)

There has been a Significant Height Revision to a hill that was surveyed for 400m Sub-Pedwar status with the Trimble GeoXH 6000, with the survey that resulted in this significant height revision taking place on the 3^rd October 2017 in good, clear conditions.

The criteria for the list this hill was surveyed for are:

Y Pedwarau – All Welsh hills at or above 400m and below 500m in height that have 30m minimum drop.  Whilst the criteria for 400m Sub-Pedwar status is all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.

The name of the hill is Pawl Hir and it is situated in the Fforest Glud range of hills which are in the eastern part of Mid and West Wales (Region B, Sub-Region B1), and the hill is positioned between the town of Llandrindod (Llandrindod Wells) to its west north-west and the small community of Hundred House to its south.

Pawl Hir (SO 101 595)

As the summit of the hill is not on designated open access land permission to visit should be sought, for those wishing to do so the nearest public footpath crosses the hill from a west – east direction and just bi-passes the two high points of the hill, one of which is situated on the northern part of the summit area and the other on the southern part, with the easiest and most convenient ascent being from the east following the footpath up the hill from the convenience of a sharp corner on a minor lane, where there is adequate parking for a car.

Prior to the survey with the Trimble GeoXH 6000 the hill was noted with 19m of drop based on the 408m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and the 389m bwlch spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website, this latter map also gives a 407m spot height to the south south-west of the 408m summit spot height.  Therefore, the purpose of the survey was to ascertain the high point of the hill and determine if it had the minimum of 20m of drop required to be classified as a 400m Sub-Pedwar.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

In all four points were surveyed for the high point of this hill; one on the northerly land where the 408m spot height appears and three on the southerly land where the 407m spot height appears, these results are given below:

1^st survey, 408m spot height – 404.903m (converted to OSGM15) at SO 10225 59703

2^nd survey, 407m spot height – 405.785m (converted to OSGM15) at SO 10108 59510

3^rd survey, 407m spot height – 405.359m (converted to OSGM15) at SO 10036 59429

4^th survey, 407m spot height – 405.641m (converted to OSGM15) at SO 10027 59400

Although the three survey results obtained on the southerly high point of this hill do not come within the parameters of the Significant Height Revisions used within this page heading, the survey result obtained on the northerly high point does, and therefore this is worth recording, 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.

The highest height obtained with the Trimble GeoXH 6000 compared to where each spot height appears on the ground is given below:

408m spot height - 404.903m (converted to OSGM15) at SO 10225 59703

407m spot height – 405.785m (converted to OSGM15) at SO 10108 59510

Although the position where the 408m spot height appears on the ground is not the high point of the hill, the result produced by the Trimble GeoXH 6000 for this position does come within the above parameters.  

Therefore, this hill’s new summit height is 405.8m (converted to OSGM15) which is positioned on the southerly land of this hill’s summit area, whilst the 404.9m (converted to OSGM15) surveyed height which is positioned on the northerly land of this hill’s summit area is 3.1m lower than the Ordnance Survey 408m spot height that appears on the 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Cardinal Hill:  Gilwern Hill

Summit Height (New Height):  405.8m (converted to OSGM15)

Name:  Pawl Hir

OS 1:50,000 map:  148

Summit Grid Reference:  SO 10108 59510

Drop:  16.9m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the northerly high point of this hill which resulted in this point's significant height revision

For details on the survey that ascertained an accurate summit height for this hill

Myrddyn Phillips and Aled Williams (December 2017)