Banc y Celyn (SO 047 464) – Subhump reclassified to Hump
This is the twenty eighth in a series of Hill
Reclassification posts that detail hills whose status has been altered in the
listing of the Humps (HUndred Metre
Prominences) through map study and / or surveys that I have conducted.
This and forthcoming posts are retrospective as many of these
hill reclassifications were initiated from studying the Ordnance Survey enlarged
mapping that is hosted on the Geograph website, and also in this instance the
Ordnance Survey 1:25,000 Explorer map, with the subsequent survey with the
Trimble GeoXH 6000 confirming these initial investigations, and for the
reclassifications that affected the Humps
the details relating to this hill were sent to Mark Jackson via email on the 14.12.11
with the survey of this hill that finally confirmed its reclassification to Hump status taking place on the 18.08.15.
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.
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| More Relative Hills of Britain by Mark Jackson |
The details for the reclassification appear below:
There has been a reclassification to the listing of the Humps (HUndred Metre Prominences) due to
consulting the Ordnance Survey enlarged mapping hosted on the Geograph website
and the Ordnance Survey 1:25,000 Explorer map, with these details sent to Mark
Jackson via email on 14.12.11, and the confirmation of this hill’s reclassification
via a survey with the Trimble GeoXH 6000 which took place on the 18.08.15.
Prior to the survey with the Trimble GeoXH 6000 Mark Jackson
had listed this hill with c 97m of drop based on the 472m summit spot height given
to a triangulation pillar on the Ordnance Survey 1:50,000 Landranger and
1:25,000 Explorer map and an estimated bwlch height of c 375m based on bwlch
contouring at 10m intervals.
The details relating to this hill’s drop and its status had
previously been discussed by Mark Jackson and other DoBIH editors prior to him receiving
the email on the 14.12.11, with much of the discussion centred on a series of
levelled heights that appeared on the Ordnance Survey Six-Inch map, an extract from
this series of maps appears below, and even though these levelled heights were
not placed where interpolation would position the critical bwlch and the publicly available 1:25,000 Explorer map showed a 372m spot height
where interpolation of bwlch contouring would place the critical bwlch, and
therefore giving this hill 100m of drop, its reclassification was not accepted. After much debate and analysis one of the DoBIH editors concluded that Banc y Celyn only had a 6% probability of qualifying as a Hump.
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| Extract from the Ordnance Survey Six-Inch map showing the series of levelled heights everywhere but the bwlch of this hill |
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| Extract from the Ordnance Survey 1:25,000 Explorer map showing the 372m spot height at this hill's bwlch |
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| Extract from the Ordnance Survey enlarged mapping hosted on the Geograph website showing the 372m spot height at this hill's bwlch |
The hill is adjoined to the Mynydd Epynt group of hills and
is situated overlooking the A 470 road and the Afon Gwy (River Wye) to its east
and the B 4520 road to its west, with the town of Llanfair-ym-Muallt (Builth
Wells) positioned towards the north.
The bwlch of Banc y Celyn was surveyed using a Trimble GeoXH
6000 by Myrddyn Phillips on the 18.08.15 resulting in a 369.9m (converted to
OSGM15) height, and when coupled with this hill’s 472m summit height this value
gives the hill 102m of drop, which is sufficient for its reclassification to Hump status.
The reclassification of this hill from Subhump to Hump status
was accepted by Mark Jackson on the 20.12.15 and the listing of the Humps was updated accordingly.
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| Gathering data with the Trimble GeoXH 6000 at the critical bwlch of Banc y Celyn |
The full details for the hill are:
Name: Banc y Celyn
Summit Height: 472m
OS 1:50,000 map: 147
OS 1:25,000 map: 188
Summit Grid Reference:
SO 04769 46438
Drop: 102m
Myrddyn Phillips (November 2017)
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