Allt y Genlli (SN 985
950) – Sub-Trichant reclassified to Trichant
THIS HILL HAS SUBSEQUENTLY BEEN RE-INSTATED TO SUB-TRICHANT STATUS
The following details have been superseded by a survey conducted by John Barnard, Chris Crocker and Graham Jackson using a Leica GS15 with the result that this hill has been re-instated to Sub-Trichant status with 28.7m of drop.
There has been a reclassification to the listing of the Y Trichant due to analysis of LIDAR data by Aled Williams. Y Trichant is the title for the hills in the 300m height band of the Twmpau (thirty welsh metre prominences and upward) and takes in all Welsh hills at or above 300m and below 400m in height that have a minimum 30m of drop, with the introduction to the re-naming of this list appearing on Mapping Mountains on the 13th May 2017.
The hill was listed in the sub category that accompanied the
original Welsh P30 lists when published on Geoff Crowder’s v-g.me website, this
sub category has now been standardised and named the Sub-Trichant and comprises all Welsh hills at or above 300m and
below 400m in height with 20m or more and below 30m of drop.
Prior to analysis of LIDAR data the hill was
listed as a Sub-Trichant and its
reclassification is dependent upon its adjacent southerly hill of Mynydd Garth Pwt, because of this the previously listed details
of both hills based on map data are given below:
Allt y Genlli (previously listed as a Sub-Trichant)
Summit Height: 394m
(OS 1:25,000 Explorer map)
Summit Grid Reference:
SN 985 950
Bwlch Height: 367m
(OS enlarged mapping hosted on the Geograph website)
Bwlch Grid Reference:
SN 983 944
Drop: 27m
Mynydd Garth Pwt (listed as a Trichant)
Summit Height: 397m
(OS 1:50,000 Landranger and 1:25,000 Explorer maps)
Summit Grid Reference:
SN 981 941
Bwlch Height: c 325m
Bwlch Grid Reference:
SN 973 941
Drop: c 72m
The hill is a part of the Pumlumon
range of hills with its Cardinal Hill being Bryn Amlwg (SN 921 973) and is placed in the Region of Mid and West
Wales (Region B, Sub-Region B2). The
hill is situated to the south of the A 470 and is positioned between the small
communities of Carno to its west
north-west and Clatter to its east.
The upper part of the hill is a part of designated open
access land, however it is also immersed in conifer plantation with its summit encircled
by a forest track, and for those who wish to visit its high point an approach
from the north using this track may be the best option.
The name of the hill is Allt y Genlli and its reclassification from Sub-Trichant to Trichant status
is dependent upon its adjacent southerly hill of Mynydd Garth Pwt and the analysis of LIDAR data by Aled
Williams. LIDAR (Light Detection & Ranging) is
highly accurate height data that is now freely available for much of England
and Wales.
Aled’s analysis of LIDAR data gives these two
hills the following details:
Allt y Genlli
Summit Height: 398.9m
Summit Grid Reference:
SN 98508 95042
Bwlch Height: 325.7m
Bwlch Grid Reference:
SN 97387 94159
Drop: 73.2m
Mynydd Garth Pwt
Summit Height: 397.8m
Summit Grid Reference:
SN 98154 94173
Bwlch Height: 367.3m
Bwlch Grid Reference:
SN 98385 94438
Drop: 30.5m
Therefore, as the 398.9m LIDAR data produced for
the summit position of Allt y Genlli
at SN 98508 95042 is higher than the 397.8m LIDAR data produced for the summit position of Mynydd Garth Pwt at SN
98154 94173, the listed bwlch position of each hill is swapped as the lower
bwlch is the critical bwlch for the higher of the two hills.
The full details for the two hills are:
Cardinal Hill: Bryn
Amlwg
Summit Height: 398.9m
(LIDAR data)
Name: Allt y Genlli
OS 1:50,000 map: 136
Summit Grid Reference:
SN 98508 95042
Drop: 73.2m (LIDAR
data)
Cardinal Hill: Bryn
Amlwg
Summit Height: 397.8m
(LIDAR data)
Name: Mynydd Garth Pwt
OS 1:50,000 map: 136
Summit Grid Reference:
SN 98154 94173
Drop: 30.5m (LIDAR
data)
My thanks to Aled Williams for sending the details of this
hill to me.
Myrddyn Phillips (May 2017)
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