Mapping Mountains – Hill Reclassifications – Humps

Foel (SH 450 506) – Subhump reclassified to Hump

This is the seventeenth 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 instigated.

Foel (SH 450 506)

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, or in this instance from a survey with the Trimble GeoXH 6000, and for the reclassifications that affected the Humps the first survey of this hill took place on the 30.12.13.

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 reclassification appear below:

There has been a reclassification to the listing of the Humps (HUndred Metre Prominences) instigated by a survey with the Trimble GeoXH 6000 and which was later confirmed by a survey with the Leica GS15.

Prior to the survey with the Trimble GeoXH 6000 Mark Jackson had listed this hill as a Subhump with c 99m of drop based on the 223m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 124m based on bwlch contouring at 10m intervals. 

The hill is adjoined to the Moel Hebog group of hills and is situated overlooking the A 487 road which is to its east and the Afon Llyfni which is to its north, with the small community of Pen-y-groes to the north-east and Clynnog Fawr to the west south-west.

Foel was surveyed using a Trimble GeoXH 6000 by Myrddyn Phillips on the 30.12.13 resulting in a 100.9m drop value, the hill was then re-surveyed with the Trimble GeoXH 6000 on the 02.02.14 resulting in a 101.6m drop value, it was then again re-surveyed on the 16.02.14 by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica GS15 and Trimble GeoXH 6000 resulting in a 101.2m and 101.1m drop value respectively, which is sufficient for this hill to be reclassified from Subhump to Hump status.

The reclassification of this hill from Subhump to Hump status was accepted by Mark Jackson and its new classification augmented in to the listing of the Humps in February 2014.

Gathering data with the Trimble GeoXH 6000 at the summit of Foel

The full details for the hill are:

Name:  Foel

Summit Height:  221.3m (as listed in the Humps, 221.4m converted to OSGM15)

OS 1:50,000 map:  115, 123

OS 1:25,000 map:  254

Summit Grid Reference:  SH 45025 50677

Drop:  101.2m (converted to OSGM15)

Myrddyn Phillips (October 2017)

Mapping Mountains – Trimble Surveys – Moel Hebog

16.02.14  Foel (SH 450 506)

This is the third Trimble survey of Foel, to read the post on the first survey of Foel please click {here} and for the second please click {here}

Foel (SH 450 506)

Before detailing the third survey of Foel (SH 450 506) it may be best to outline a recent visit to Daresbury that John and I made to gather Trimble data at its Ordnance Survey Fundamental Benchmark (the height and position of Fundamental Benchmark’s are known to a high degree of accuracy).  The data sets collected indicated that there is a systematic error occurring of approximately 10cm when the Trimble is positioned on a pole with its external antenna.  However, further tests are required which have already started.

The third survey was a combined effort with Leica and Trimble technology employed.  The previous two surveys had resulted in 221.4m summit; 120.5m bwlch with 100.9m drop (1^st survey) and 221.7m summit, 120.1m bwlch with 101.6m drop (2^nd survey).  However, the first bwlch survey never attained the required o.1m accuracy and was the reason why the second survey took place and the second summit survey used the pole and external antenna and was positioned a few centimetres higher than the first summit survey position.  If the first bwlch and second summit results are discounted it indicates that the summit of Foel is 221.4m (plus about 7cm) and the bwlch is 120.1m, giving a drop of 101.4m.  It’ll be interesting to see how the processed results from the third survey compare to these measurements.

John, Graham and I met in the car park opposite the Texaco garage in Pen-y-groes (SH 470 529).  We drove through Llanllyfni and parked at SH 458 500, this is at the start of the track that leads to Llwyn Bedw Uchaf and crosses the critical bwlch.  As we got our boots on (wellies for me!) the sky was a radiant blue and the weather forecast was good for the rest of the day, which made a change from the incessant rain that had been sweeping over the country for weeks upon end.

We had a quick look at the area of the bwlch when we walked down the track and then headed for the summit.  Half an hour after leaving the cars we were approaching the final few metres of ascent.  John and Graham used the level and staff to find the highest part of the hill whist I noted all measurements and tried frantically to take a few photos in between plotting where each staff position was in relation to the position of the level and the summit cairn.  The highest point proved to be where the second Trimble summit survey had taken place; unfortunately we couldn’t take a relative height reading with the staff between the first and second survey positions as the Barnard boot had made a severe indent in the ground!

Surveying for summit position.

The Leica GS15 was soon set up on its 2m pole over the high point of Foel and we stood with our backs to the chilly breeze and chatted, eventually we took shelter on the leeward side of the breeze.  By this time cloud had materialised over Bwlch Mawr (SH 426 478), its bulbous nature was reminiscent of a volcanic explosion that had its centre at the summit of Bwlch Mawr, spewing its ash cloud inland to the higher peaks of Eryri.

The Leica GS15 set up on its 2m pole at the summit of Foel.

Once the Leica GS15 had gathered an hour of data we positioned the Trimble on the high point and gathered 11 minutes of data.  With all required summit data collected we reversed the inward route and headed down to the area of the bwlch, calling in at Llwyn Bedw Uchaf on the way to ask permission to take readings in the fields either side of the track.

The Trimble GeoXH 6000 gathering data at the summit of Foel.

We each placed a flag in the ground at the position where we thought the critical bwlch lay.  This is a practice we aim to do on most of the G&J Surveys outings as it will help in comparing how bwlch and also summit position is judged purely using eyesight when compared to the added advantage of using a surveyor’s level and staff.  I’m proud to say that my flag won – YYIIPPPEEEE!!!!

Surveying for bwlch position.

The critical bwlch was found to be positioned within 2cm in height and about 1m in position from each of the previous Trimble bwlch surveys.  John then assembled the Leica GS15 in a convenient spot in the field to the south of the track, whist I headed in to the field to the north of the track to chat with a farmer who had come up on quad bike to check on what we were doing.  He was the owner of the land that takes in the summit of the hill as well as the field to the north of the track.  We chatted for ten minutes or so and I explained why three people were wandering around with all manner of unusual looking bits of equipment.  He didn’t mind at all that we had visited the summit and kindly gave permission for us to take readings in the field and seemed quite interested in everything we were doing.  By the time I’d re-joined John and Graham the measurement offset between the critical bwlch and the Leica GS15 set up position had been measured with the level and staff.

Another hour of data was collected by the GS15 before we took three data sets with the Trimble.  Two on the Leica 2m pole (one calibrated to the ‘Top of notch’ and the next to ‘Bottom of antenna mount’) and the third with the Trimble positioned on the ground.  This will give us three sets of data to compare to the GS15 measurement and may answer the question why the Trimble seems to have a 10cm systematic error when operating with its external antenna on a pole.

John beside the Trimble set up position at the bwlch of Foel.

Five hours after setting off for the hill we arrived back at the cars.  John and Graham headed back to Mold and Chester respectively whilst I navigated my way around the narrow lanes to visit Mynydd Cennin (SH 458 449).

Survey Result:

Foel

Summit Height:  221.3m (converted to OSGM15, Trimble)  221.4m (converted to OSGM15, Leica GS15)

Summit Grid Reference:  SH 45021 50673

Bwlch Height:  120.2m (converted to OSGM15, Trimble)  120.2m (converted to OSGM15, Leica GS15)

Bwlch Grid Reference:  SH 45818 50103

Drop:  101.1m (Hump addition confirmed)

Dominance:  45.72%

The average of the three data sets for the Trimble bwlch data is 120.166m (converted to OSGM15) which is in good accordance with the 120.159m (converted to OSGM15) attained from the Leica GS15. 

For further details please consult the Trimble survey spreadsheet    click {here}

Mapping Mountains – Trimble Surveys – Moel Hebog

02.02.14  Foel (SH 450 506)

This is the second of three Trimble surveys of Foel, to read the first survey post please click {here} and the third please click {here}

Foel (SH 450 506)

The first survey of Foel was conducted late in the afternoon on the 30^th January and produced a drop result of 100.9m.  As the hill is currently listed as a Sub-Hump with 99m of drop I wanted to repeat the survey to compare data sets, but also attain adequate bwlch data as the previous data set had a high standard deviation and its estimated accuracies was also poor.

I was at the base of the hill by 10.00am and walked down the track to the position of the bwlch.  Thankfully the weather was set fine for most of the day and the sun was shining through the trees that lined the sides of the track.

On my previous visit the Trimble had been placed beside the track for it to gather data with its internal antenna, it never achieved its 0.1m accuracy which indicates that the equipment is ready to ‘Log’ data.  This may be due to the closeness of trees at the position of the bwlch, as activating the equipment before the required accuracy had been attained probably resulted in the poor data set that was gathered. 

For this second survey I’d come fully prepared with pole, tripod and external antenna.  I wanted to place the equipment in the same position as I had done during the first survey and within a few minutes the Trimble was connected to its Zephyr antenna, which was mounted on the Draper tripod.

The Trimble on its Draper tripod beside the track at the bwlch

The advantage of the Draper tripod is that it only weighs 1Kg which is beneficial when carrying a lot of surveying gear around the hills.  It was Alan Dawson who first showed me the tripod whist in Scotland last year.  Another advantage is its cost as it’s less than £20.00 including postage and packing from good retail outlets on the Internet.  However, its weight is also its major disadvantage as any strong wind would probably blow it over.  A freshening wind was forecast for the morning so I hoped the low elevation and sheltered spot of the bwlch would enable the Trimble to be set up on its tripod. 

During the first survey of the bwlch the required accuracy of the Trimble slowly edged its way down to the required 0.1m but only ever attained 0.12m and then bounced back up to over 1.0m.  This happened on three or four occasions and was the reason why I activated the equipment to gather data with the 0.1m accuracy not being attained.  Once the Trimble was set up on the Draper tripod I wondered if I was in for a long wait for the accuracy to be attained, if it ever was attained.  After about a minute I looked at the screen and thankfully the 0.1m accuracy was showing, I pressed ‘Log’ and stood away from the equipment a few metres up the lane.

The Trimble positioned at the bwlch with Foel in the background

The track crosses the bwlch on the hill to hill traverse.  With the valley to valley traverse bisecting the track at the approximate position of the Trimble.  The field on the left of photo was visually dismissed as lower than the track, whilst the field on the right of photo had data gathered in two positions during the surveys

During this process a number of cars and vans had pulled up and parked next to my car, which was only a couple of minutes’ walk away.  A number of people walked across the adjacent field, rifles in hand and after another few minutes a couple came down the lane to investigate what I was doing.  We chatted for ten minutes, I explained why I was there and what a Hump was, they seemed a little interested and slightly bemused but did not mock!  They were out trying to find a fox that had been taking chickens from two nearby farms.  I asked if it was all right to visit the summit and also the adjacent field, they didn't mind at all.

The field that was visually dismissed as lower than the track is on the right of this photo

After 20 minutes of data had been gathered I packed the equipment away and headed up to the summit.  The mark where the Trimble had been set up on the ground beside the summit cairn on the 30^th January was still there, but I chose a slightly different spot about 20cm away that seemed a little higher.  As a brisk breeze was blowing across the hill I employed a method used by Alan Dawson and pushed the pole in to the ground, attached the external antenna, connected it to the Trimble and measured the distance between the tip of the screw thread just below the bottom of the antenna and the ground, and input this in to the equipment as a measurement offset.  The 0.1m accuracy was soon attained and another 20 minutes of data was gathered.

The set up position next to the summit cairn

The Trimble set up at the summit with Bwlch Mawr (SH 426 478) in the background

During this wait I wandered around the earthen ramparts of the ancient hill fort and took a number of photos of the equipment.  The hill has good views from its summit with the coastline heading north toward Caernarfon and Ynys Môn and the Yr Eifl range of hills on view toward the south-west.

The screen on the Trimble, giving 21 satellites locked onto, battery approximately half full, 10cm accuracy attained and 321 points (seconds) of data gathered.

After the equipment had been packed away I headed back to the bwlch as I wanted to get a data set from the adjacent field.  I’d done the same thing during the first survey, as I’d now got permission to visit the field I had confidence in wandering about assessing the line of the bwlch on the valley to valley traverse.  The conclusion was the same as last time; the critical bwlch is placed on or beside the track.  I picked a spot close to a telegraph pole and placed the Trimble on the grass in the field and collected 11 minutes of data with its internal antenna, and happy in the knowledge that I’d done as much as I could with the equipment at hand I headed back to the car.

Survey Result:

Foel

Summit Height:  221.7m (converted to OSGM15)

Summit Grid Reference:  SH 45021 50673

Bwlch Height:  120.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 45819 50104

Drop:  101.6m

Dominance:  45.82% (final 3rd survey gives 45.72% Dominance)

The first survey gave a drop of 100.9m with an inadequate data set from the bwlch.  The second survey gives 101.6m with a good data set from the bwlch and a slightly higher summit value, which is partly based on a slightly higher position for the Trimble.  On each survey data was gathered from a position in the adjacent field to the bwlch, both results show map contouring at the bwlch to be on the high side as each result is just below 120m.  Therefore this hill is a proposed new Hump.

For further details please consult the Trimble survey spreadsheet click {here}

Mapping Mountains – Trimble Surveys – Moel Hebog

30.12.13  Foel (SH 450 506)

This is the first of three Trimble surveys of Foel, to read the post on the second survey of Foel please click {here} and the third please click {here}

Foel (SH 450 506).

Although west of the A487 road, Foel (SH 450 506) is adjoined to Crib Nantlle and therefore part of the Moel Hebog group of hills.  It is listed as a Sub-HuMP and a Welsh 200m P30 with c 99m of drop.

 

Visiting this hill was somewhat rushed as I planned to look at one or two hills above Blaenau Ffestiniog, but after waiting almost two hours for the rain to stop I gave up and headed towards Nantlle where the murk and wetness had already cleared eastward.  With only an hour or so of daylight remaining options were limited, but Foel was feasible in the time left before darkness and when approaching the hill from the south-east its bwlch is on the way up to its summit.

I had a quick look at the area of the bwlch on my way up the track that goes to Llwyn Bedw Uchaf, the track seemed to be where the critical bwlch was placed, and this also matched what contour interpolation suggested on the map.

The whole hillside was sodden due to the heavy and persistent rain that north-west Wales had been experiencing for a number of days.  The upper section of the hill has the remains of an ancient hill fort on it.  I placed the Trimble on the ground beside the cairn, having dug down beyond the grass creating a flatbed for it to nestle in.  The sun was just disappearing behind the higher hills of Yr Eifl and after five minutes of data collection I was away and down to the area of the bwlch as quickly as my legs could take me.

The Trimble beside the cairn on the summit of Foel.

Grass has now grown over many of the lower rocks of the summit cairn.

I took two readings from the bwlch area, one beside the track which seemed to be the high point of the valley to valley traverse and which also followed the direction of the hill to hill traverse, and a second reading in an adjacent field beside a large puddle of standing water.  By the time I got back to my car I just had enough time to change before darkness set in. 

Trimble in field next to standing water.  The hedge (left) and track (upper centre) give an inclination toward where the low point of the hill to hill traverse is positioned.

The Trimble beside the track that crosses the critical bwlch.

Same position, but different view of the Trimble beside the track that crosses the critical bwlch.

Survey Result:

Foel

Summit Height:  221.4m (converted to OSGM15)

Summit Grid Reference:  SH 45022 50673

Bwlch Height:  120.6m (converted to OSGM15)

Bwlch Grid Reference:  SH 45818 50104

Drop:  100.9m 

Dominance:  45.56% (final 3rd survey gives 45.72% Dominance)

An interesting result, as if confirmed this hill will be a new Welsh Hump.  However, the Trimble was activated before the recommended 0.1m accuracy had been attained during the survey of the bwlch and the standard deviation shows a relatively high figure of 0.7m and the estimated accuracy is also poor.  The second point surveyed at the bwlch, which was in the adjacent field, has 0.0m for standard deviation and a good estimated accuracy with an absolute height of 119.9m, indicating the height of the bwlch to be on the low side when compared to its c 120 – c 130 map contouring.

For further details please consult the Trimble survey spreadsheet click {here}