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)