Mapping Mountains – Hill Reclassifications – Humps

Old Radnor Hill (SO 251 587) – Recommended Subhump deletion

This is the thirty second in a series of Hill Reclassification posts that detail hills whose status has either been altered in the listing of the Humps (HUndred Metre Prominences) through map study and / or surveys that I have instigated, or it is the recommendation that their status is altered.

The remains of Old Radnor Hill (SO 251 587)

Many preceding posts detailing these alterations to the Humps are retrospective as these hill reclassifications were either initiated from studying the Ordnance Survey Interactive Coverage Map that is hosted on the Geograph website, or initiated from a survey with the Trimble GeoXH 6000, and for this recommended deletion that affects the Humps the survey of this hill took place on the 11.01.14 with LIDAR analysis conducted on the 20 & 21.09.18.

The listing of Humps was published in book format by Lulu in 2009 and entitled More Relative Hills of Britain, its author; Mark Jackson gives credit to a number of people who contributed toward the formation of this list, these include; Eric Yeaman, Alan Dawson, Clem Clements, Rob Woodall, Bernie Hughes, Pete Ridges and others.  When the list was published in book format there were 2987 Humps listed with their criteria being any British hill that has 100m or more of drop, accompanying the main list is a sub category entitled Subhumps, with the criteria being any British hill that has 90m or more and below 100m of drop.

More Relative Hills of Britain by Mark Jackson

The details for the recommended deletion appear below:

There has been a recommended deletion to the listing of the Humps (HUndred Metre Prominences) instigated by a survey with the Trimble GeoXH 6000 which took place on the 11.01.14 and subsequent LIDAR analysis conducted by Myrddyn Phillips.

This hill has a convoluted history of classification within the Humps and prior to LIDAR analysis the hill had previously been listed as a Hump with a 327m summit height and 110m of drop, due to the hill being quarried its drop value was reduced in April 2011 to c 100m based on a reduction in its estimated summit height to c 317m, with it still retaining its Hump status.  The hill was then reclassified to a Subhump in January 2013 based on a 222m bwlch height which gave the hill c 95m of drop.  As well as the summit being reduced in height due to quarrying, there is a road cutting to the east of the hill which if taken as a part of the hill’s drop would increase this value.  The hill was subsequently surveyed with the Trimble GeoXH 6000 resulting in a 312.6m (converted to OSGM15) summit height and a 222.7m (converted to OSGM15) height to what was judged to be the highest remaining natural ground of the critical bwlch, and a 215.6m (converted to OSGM15) height to the road cutting, resulting in an 89.9m and 97.1m drop respectively.  With the hill being temporarily deleted from Subhump status on the 13.09.14 based on the drop value being taken to what was judged to be the highest remaining natural ground of the critical bwlch.  The re-instatement of this hill to Subhump status was based on the survey taken to the road cutting and was accepted by Mark Jackson and it was added to the listing of the Humps on 22.12.15.

The hill is adjoined to the Fforest Glud range of hills and is situated overlooking the A 44 road to its east, and has the small community of Walton towards the north-north-east and Old Radnor towards the north-west.

The recommendation of this hill’s deletion from Subhump status is based on LIDAR analysis coupled with the summit survey using the Trimble GeoXH 6000.  LIDAR gives the summit of this hill as 319.4m at SO 25177 58811, whilst the survey with the Trimble produced a summit height of 312.6m (converted to OSGM15) at SO 25135 58770, the discrepancy in height is due to quarrying activity between the date that LIDAR was produced and the survey using the Trimble.

The listed drop valley of this hill will be based on the height and position of its bwlch.  An on-site inspection of this bwlch during the survey with the Trimble concluded that the natural bwlch had been terra-formed and lay in a Chapel, this is placed beside a minor road, which is placed above the A44 road which forms a cutting, all three are placed on the hill to hill traverse associated with this hill.  Therefore there are three options for the height and position of this bwlch.  Their respective Trimble and LIDAR data are given below:

Option 1 – natural bwlch:

Trimble:  222.7m at SO 25888 59083

LIDAR:  222.8m at SO 25887 59097

Option 2 – minor road beside Chapel:

Trimble:  not surveyed

LIDAR:  222.6m at SO 25899 59099

Option 3 – A44 road cutting:

Trimble:  215.6m at SO 25946 59114

LIDAR:  215.4m at SO 25943 59107

LIDAR contouring suggests that the natural bwlch of this hill is intact and placed beside the Chapel and an on-site inspection confirms this consists of grass.  Therefore as the A44 road cutting is man-made and the natural bwlch still exists the third option for the bwlch is dismissed.  However, the height of the minor road (option 2) beside the Chapel is lower on the hill to hill traverse compared to option 1, but LIDAR implies and the on-site inspection concluded that this minor road also forms a slight road cutting and therefore it is also considered man-made.

LIDAR image of the bwlch of Old Radnor Hill

Therefore, as LIDAR contouring implies that the natural bwlch of this hill is intact it is recommended that this hill is deleted from the status of Subhump based on Trimble GeoXH 6000 summit and LIDAR bwlch data.

The full details for the hill are:

Name:  Old Radnor Hill

OS 1:50,000 map:  148

OS 1:25,000 map:  201

Summit Height:  312.6m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SO 25122 58775 (as listed in the Humps, with the Trimble survey taken to SO 25135 58770)

Bwlch Height:  222.8m (LIDAR)

Bwlch Grid Reference:  SO 25887 59097

Drop:  89.9m (Trimble summit and LIDAR bwlch)

Myrddyn Phillips (November 2018)