05.04.22 Abberley Hill (SO 751 672)
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| Abberley Hill (SO 751 672) |
Abberley Hill was once
listed as a Marilyn, with it promoted to this status in April 1997 after
Charles Everett had conducted a plumb line survey from a road bridge passing
over the area of the col, which then consisted of an 18m deep disused rail
cutting. Its resulting reclassification
to Submarilyn status was due to a part of the cutting under the road being
infilled.
Charles had petitioned
for a number of years for us to visit this hill and survey it with the Trimble
GeoXH 6000. Covid-19 and the resulting
restrictions had scuppered any plan to do this for two years and more. However, with a forecast for a dry day, light
breeze and importantly with only the first signs of green shoots on the trees, we
decided that it was the ideal time to investigate this hill.
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| LIDAR summit image of Abberley Hill |
Its current drop value
is given as an estimated c 145m, based on a 283m summit height and an estimated
c 138m col height, with the latter taken to the road passing over the infilled
section of the cutting. Prior to
visiting I had consulted all available online maps and found the interactive
mapping on the OS Maps website of particular interest. This mapping shows the 130m contour broken at
two points, one is under the road where the infill is positioned and the other
is approximately 100 metres to the north.
The shape of these contours implies that the col at the cutting is
intact and is not placed under the infill, with the road col only taken because
of the infill. One could argue that if
the cutting was taken as a part of the drop value for this hill, which it was,
then its intact col should be prioritised over that of man-made infill. This premise is complicated as a cutting is also
man-made. However, an important
difference is that a cutting exposes natural ground, whilst infill is
artificially raised deposited ground.
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| LIDAR col image of Abberley Hill |
We set off with
intention to survey the col adjacent to the road and investigate what remains
of the cutting below the road and confirm whether the col in the cutting as
implied by contours on the OS Maps website, exists on the ground and is intact.
The road passing over
the infill is a part of the B4202 and connects the small community of Abberley
Common to its south with Cleobury Mortimer to its north. I considered parking my car on the road and
placing the Trimble on the roof and using my surveying steps to gain elevation
to see the screen and gather data this way.
However, although the steps were in my boot, there is a convenient track
with a wide entrance leading to works just to the east of the road bridge. Upon inspection this was also where we
considered the road col to be placed, which is confirmed by the position
obtained from LIDAR analysis. Before
setting the Trimble up I re-positioned my car further down the track so as not
to interfere with satellite reception.
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| The Trimble GeoXH 6000 set-up position at the road col |
As the Trimble quietly
beeped away gathering its individual datum points I stood with Charles on the
narrow grass verge on the northern side of the road bridge, this encouraged any
traffic heading south-east to veer away from us and by doing so also the
position of the Trimble as they sped across the bridge. Once five minutes of data were gathered and
stored I closed the equipment down, took a few photographs and packed it away. I then re-positioned my car at the entrance
of the wide track before we headed down in to the remains of the cutting.
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| Gathering data at the road col of Abberley Hill |
A gap in a fence gave us
a convenient point of entry to the land descending in to the cutting. Once through the fence it was like venturing
in to a different world. For all intents
and purposes the cutting is now a dingle; it is overgrown with all sorts of
vegetation with many mature trees heading skyward.
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| Charles heading down to the bottom of the cutting |
At the bottom of the
cutting is a brook which flowed toward the steep infill and road which was now
quite a height above us. The brook feeds
in to a wide drainage tunnel which no doubt deposits the water out on the other
side of the landfill to the south of the road.
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| The drainage tunnel under the infilled road bridge |
The direction of water
flow was encouraging as it meant higher ground was to our north. We followed this ground for about 100 metres
and found the brook disappeared and the ground rose to a point that we easily
identified as the intact col at the remains of the cutting. From this point the ground then descended
north. We were now at the col that is
shown on the interactive mapping available on the OS Maps website.
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| Charles at the col in the cutting |
Ideally Trimble data
should now be collected from this point.
However, its position was not encouraging for any form of adequate
satellite reception, as with a canopy of trees and branches immediately above;
in all likelihood data would be compromised.
But as we were now here I wanted to try, even though the processed height
would no doubt be compromised, the Trimble would at least give a good reading
for position.
As Charles found himself
a spot to lie down and relax, I set the Trimble up and proceeded to listen to
it objecting to its position. This emanated
with it screeching; an indication that all was not going well and that the recommended
minimum of five satellites required for logging data, was not being achieved. I persevered and eventually gathered 153
individual datum points, more that the 12o minimum recommended by the
manufacturers.
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| The Trimble GeoXH 6000 set-up position at the col in the cutting |
Once data were gathered
and stored we headed back to the brook and the wide drainage tunnel to
investigate the landfill. From here the
land rose steeply up to the base of the road which could be seen above with the
occasional high sided van and lorry speeding across the under filled road
bridge.
We made good progress up
the landfill using small rooted trees to help our passage. However, we were barred from reaching the
base of the road by large amounts of hawthorn.
It would have been ideal to reach this point and confirm the landfill to
be immediately under the road with no sign of light through to its southern
side, but from the vantage point we had reached it looked as if this was so,
and with any further progress now barred by copious amounts of hawthorn, we
headed back down toward the brook and then up to the fence and my awaiting car.
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| Our high point on the infill; beyond the saplings is a mass of hawthorn |
With the first part of
the survey of this hill now complete we headed south to the small community of
Abberley Common and connected with the narrow road that makes its way over the
northerly part of the hill. We found a
convenient parking place just below where a public footpath sign indicated the
way to the summit of Abberley Hill.
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| Starting on the path leading to the top of Abberley Hill |
The path to the summit
proved a delight as it meandered uphill through deciduous woodland that must be
ablaze with colour during the height of the autumnal season. Charles led the way and I contentedly
followed. As we gained height the
triangulation pillar positioned at the summit came in to view. All that remained was to gather Trimble
data. However, this was easier said than
done.
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| Approaching the summit of Abberley Hill |
The triangulation pillar
atop Abberley Hill is given a height of 283m and is positioned about one metre
from a corner fence post with land at the base of this post regarded as the
summit of the hill. However, the
Ordnance Survey 1:25,000 Explorer map gives an uppermost 285m contour extending
from the area of the trig pillar out toward its north-west taking in a part of
the woodland. This is also where LIDAR
analysis places the summit. But the
height of this upper contour is considered erroneous and as LIDAR is also prone
to give erroneous readings in woodland, I decided to gather data from what many
consider as the summit and that is land immediately below the corner fence
post.
On our way to the trig
pillar I had walked over where LIDAR places the summit, the ground hereabouts
was an obvious contender for summit position, but only an optical level would
be able to judge whether it was higher than ground at the base of the corner
fence post.
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| The Trimble GeoXH 6000 set-up position at the summit of Abberley Hill |
It took an inordinate
amount of time until I activated the Trimble, during which I sat beside Charles
and we chatted, whilst the equipment ever so slowly ebbed down to the 0.1m
accuracy level before data should be logged.
Eventually the Trimble was quietly beeping away gathering its individual
datum points, but as its position was pointing in to woodland with trees overhead,
data may be compromised.
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| Charles beside the trig pillar |
Once five minutes of
data were gathered and stored I closed the equipment down, took a series of
photographs with it still positioned on the fence post and then packed the
Trimble away. Our downward route
retraced our inward and we were soon back at the car and heading toward our
next hill of the day.
Survey Result:
Abberley Hill
Summit Height: 283.4m (LIDAR)
Summit Grid Reference: SO 75140 67221 (LIDAR)
Col Height: 138.9m (converted to OSGM15, Trimble GeoXH
6000) (road above infill)
Col Height: 125.2m (LIDAR) (col at cutting)
Col Grid Reference: SO 70158 74645 (Trimble GeoXH 6000) (road
above infill)
Col Grid Reference: SO 70131 74751 (LIDAR) (col at cutting)
Drop: 144.5m (LIDAR summit and Trimble GeoXH 6000 col)
(road above infill col)
Drop: 158.2m (LIDAR summit and col) (cutting for
col)
Dominance: 51.00% (LIDAR summit and Trimble GeoXH 6000
col) (road above infill col)
Dominance: 55.81% (LIDAR summit and col) (cutting for
col)
For further details please consult the Trimble Survey Spreadsheet
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