Mapping Mountains – Trimble Surveys – Brown Clee Hill

05.04.22  Abberley Hill (SO 751 672)

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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