Monday, 28 April 2014

Hill Lists – Cymru / Wales – 200m Twmpau updates – Pen Llŷn



The first list to the Welsh 200m P30 hills was published on Geoff Crowder’s website v-g.me in 2000; this list preceded the list of TuMPs by nine years, the list proved a very useful resource for the TuMP compilation for this category of hill.

The Welsh 200m P30 list documents all hills in Wales that are at or above 200m in height and are below 300m in height, to qualify for the main list each hill requires a minimum of 30m of prominence.


The hills listed below are updates to the Welsh 200m P30 list originally published on Geoff Crowder's website.  To see the original list click {here}


The original published list had a Sub-List which was entitled ‘Hills to Survey’.  This list consisted of all hills in Wales in the stipulated height band that have a minimum of 20m of prominence, but do not meet the minimum 30m of prominence to enter the main list, according to Ordnance Survey map spot heights and contours.  Nowadays the standard Sub-List takes in all hills that have a minimum of 20m of prominence.  However, the Hills to Survey Sub-List discounted hills whose map spot heights gave a drop value of less than 30m, but more than 20m.  By doing so, the only hills that were Sub-Listed were those that map values dictated stood a chance of entering the main list, for example; if a hill had a summit spot height of 250m and a bwlch spot height of 221m, it was not listed in the Hills to Survey Sub-List as with 29m of drop I thought it did not stand a chance of main list qualification. 

When compiling the Sub-List I was measuring many hills for P30 status using a basic levelling technique, please click {here} for more information concerning this.  I now know that Ordnance Survey spot heights have a standard margin of uncertainty of + / - 3m associated with their accuracy.  Therefore many hills that were not listed in the original Sub-List may have sufficient drop to enter the main list.  Because of this the Sub-List has been altered to include all hills that have a minimum of 20m of drop but are not known to attain the minimum 30m of drop to enter the main list.

The hills listed below are those major amendments to the original Welsh 200m P30 list as it appears on Geoff’s website.  There are many hills that have been promoted from the Hills to Survey Sub-List to the main list, whilst there are many additions to the Sub-List now that it has been standardised to include all 20m minimum but below 30m drop hills.

When the 200m P30 list was first published it was the first to this category of hills and in some way it and its other 100m height band lists paved the way for Clem’s data that later appeared on the RHB file database and then for the TuMPs listing by Mark Jackson.

As well as the first P30 list to this height band the list is now the first to include a comprehensive Sub-List.

TuMP baggers beware; as the main list also includes P30’s not listed by Mark Jackson, so if you want to visit all P30’s you’ll have to include some non TuMPs to do so.

The list will be updated on a weekly basis and will be done so through each Group category, starting from the north and working south.  The third Group that has major updates is Pen Llŷn.



Pen Llŷn

West of the Afon Dwyfor and the Afon Dwyfach from SH 478 372 to SH 453 485 and continuing to the Afon Desach and Aberdesach at SH 425 514.  Bordering with Moel Hebog to the east.



Twmpau - 200m updates

Moel Caerau    207m    SH 292 354

This hill was always a prime candidate for promotion from the sub-list and with the large scale Ordnance Survey mapping on the Geograph website giving a 173m spot height on the area of the bwlch it gives this hill 34m of drop.



Next update due on the 5th May 2014

Friday, 25 April 2014

Mapping Mountains – Trimble Surveys – Y Berwyn


21.04.14  Gallt y Goedhwch (SJ 137 159) and Pt. 321.1m (SJ 137 155)

Gallt y Goedhwch (SJ 137 159)
Mark suggested meeting up and had originally thought of heading for Rhobell Fawr (SH 786 256), this was quickly shelved as the forecast predicted intense thunderstorms in mid Wales for the afternoon.  The next idea was a circuit in the Howgills, but it seemed the worsening weather was going to hit that part of England as well.  However, the forecast for the morning was set fair so he suggested upping his HuMP total and visiting Gallt y Goedhwch which is situated in the tranquil lands above the Dyffryn Meifod, a few miles from Welshpool.

The hill also had the added advantage of having two similar heighted tops for its main summit which has a 325m spot height on the Ordnance Survey enlarged Geograph map, and just to the south is another summit which has a small uppermost c 320m ring contour.  This has caused a bit of debate in the past between Douglas Law, Chris Watson, George Gradwell and me.  Hopefully the Trimble could distinguish which of the two similar heighted tops is the higher, give a height to the southerly summit, confirm this to be lower than the main summit and if we surveyed the bwlch between we could also give a drop value for the southern summit.  I also hadn’t visited this hill, so it would be a new P30 tick for me.

I had suggested starting from a relatively high road and approaching the hill from the south-east, but Mark pointed out that this route had a reputation for meetings with an inquisitive farmer, so we parked at a road junction where sufficient space for at least one car can be found at SJ 139 169.  This route would also enable us to have a good walk, instead of a quick bag.

As Mark was getting his boots on I sauntered over to the near hedge row and admired the colourful crop of wild flowers, all newly sprung with that luxuriant colour of early spring, highlighted by morning sunshine.  As we started eastward down the lane toward the farm of Gwaelod (SJ 142 164) we soon encountered all manner of friendly animals from donkeys to dogs; all wanted a pat and a lot of fuss.  From this vantage point Gallt y Goedhwch rose steeply above the green fields with its lower slopes covered in deciduous woodland, it was these slopes that we hoped to gain access on through to the summit.



























We left the lane before the farm and joined a public footpath across a field which aimed for the lower reaches of the wooded slopes and a track that contoured its way around the hill.  Once in the wood we had to pick our spot when to bear left and head uphill.  Once picked, we wondered if an easier route may have existed further up the track, as our route was unforgivingly steep.  It was all rather beautiful though, as the land was covered in fallen foliage interspersed amongst mature trees, all quiet except for our labours and the welcome addition of bird song.

Crossing the field before entering the wood
The steep slopes in the wood
As height was gained we encountered a high fence, no doubt put in place for pheasant rearing.  A few minutes later and the steep slope started to relent as we came out of the wood to the northerly ridge of the hill.  Such a wonderful place to be on a morning bathed in blue sky, but we knew this was not going to last as the heat of the day was predicted to set off intense thunder showers in the early afternoon.

Emerging out of the wood on to the upper slopes of Gallt y Goedhwch
We were soon on the high point, or the two high points, we assessed the height difference between each and thought the more south-westerly one to be the higher, Mark thought by as much as 0.5m.  The Trimble was placed on each in turn, gathering ten minutes of data from both.  Each high point is easily identifiable as the summit consists of a small rocky ridge with the ground conveniently reaching its respective high points without bothersome intermediate rocky bits vying for possible other high points, outside of the two that we were now surveying and of course the other southerly summit that could be as high!!

The highest part of Gallt y Goedhwch is the south-westerly point of the main summit
Mark enjoys the rest whilst the Trimble gathers data at the north-easterly point of the main summit with the high point of the hill in the background
Once the data was stored we made our way to the bwlch between the main summit and the southerly one and had a good look at the ground, once the position of the critical bwlch was decided upon the Trimble was placed on the spot and gathered five minutes of data.

Gathering data at the bwlch between the two hills
The southerly summit is quite steep when approaching from its northerly bwlch.  The name of Maes y Castell appears on the map near to the summit of this hill but the Ordnance Survey 1:2,500 map from 1975 implies that this name is that of the farm at SJ 137 154, whilst the name of Y Bwythyn appears on the OS enlarged Geograph map, this name seems to be applicable to a cottage.  This southerly summit also consists of a small rocky ridge, within a few minutes the Trimble was balanced on top, aligned with its highest point.  Thankfully there was only a slight whisper of breeze that helped negate the heat of the sun, otherwise strong wind would no doubt have dislodged the Trimble and rolled it down the hillside.  Another ten minutes of data was collected as we lounged around in the sun and admired the view.

The Trimble GeoXH 6000 on the summit of  Pt. 321.1m (SJ 137 155)
We headed westward from the bwlch and re-joined our inward track in the wood as the blue of the sky was replaced by an ominous murkiness; heralding what we thought was the impending storm.  Thankfully this never materialised for this part of Wales as the predicted intense rain concentrated itself to the south of the country. 

Four data points gathered and hopefully a few questions answered by the results, an excellent small walk taking just over three hours.

An Easter bunny, unfortunately a dead one.  We came across this during our descent back through the wood


Survey Result:


Gallt y Goedhwch

Summit Height:  325.7m (converted to OSGM15)

Summit Grid Reference:  SJ 13709 15922

Drop:  115m

Dominance:  35.30% (Lesser Dominant status confirmed)



Pt. 321.1m

Summit Height:  321.1m (converted to OSGM15)

Summit Grid Reference:  SJ 13704 15586

Bwlch Height:  295.3m (converted to OSGM15)

Bwlch Grid Reference:  SJ 13681 15650

Drop:  25.8m (Sub-Trichant status confirmed)

Dominance:  8.03%



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

Thursday, 24 April 2014

Mapping Mountains – Trimble Surveys – Pumlumon


20.04.14  Pt. 318.8m (SN 924 853)


Pt. 318.8m (SN 924 853), bwlch on right near to farm with summit on left
I’d spent some time the previous evening trying to find two or three hills of interest whose P30 status needed checking or whose Sub status stood a chance of being promoted to full P30 status.  One that met the latter description was a hill on a descending easterly ridge to the south of Llyn Clywedog.  To make things easier the ridge that the hill is situated on has a minor road on it.  However, there are farms either side of bwlch and summit and the land looked like prime sheep grazing, and as it is now just past lambing time, these little beasts may be with their mothers on the fields I wanted to survey, so I had to show caution and respect toward the beasties.

The road from my last hill (Pt. 381.7m SN 926 875) heads south-eastward toward Llanidloes, after a mile I turned right and then a few minutes later I turned left on to a steep and seldom used road with unenclosed fields on my right, lambs scampering about and three gates to open.  I tried my utmost to encourage the lambs to stay in their given fields when opening these gates, but I’m afraid one escaped in to a neighbouring field, so no doubt she is now wandering around trying to discover a new mother.

I parked next to the entrance to the track that leads down to the farm of Upper Cefn-penarth (SN 920 855).  I’d looked at this road on Google Maps the previous evening and had noted that the ground immediately to the north of the road where a 288m spot height appears on Ordnance Survey maps was higher; I’d also zoomed up the lane toward the summit where a 317m spot height appears on the OS map.  The high point of the hill was above this road.  Could the height difference between the land at bwlch and summit be sufficient for P30 status to be confirmed?

The 288m spot height appears on this lane, the critical bwlch is higher and in the field on the right
Once out of the car I walked westward up the road to acclimatise myself with the lay of the land at the bwlch, the ground immediately north of the lane proved higher, I looked around for any farm vehicles on adjacent fields and sneaked over the fence, saying good morning to two small lambs and their mother as I did so.  No sooner was I in the field and one of these lambs walked toward me and nuzzled my leg, I ignored its advances!

I needed to be quick as I was in full view of the lane and the farm of Upper Cefn-penarth was only over the lip of the field, I spent a few minutes on my knees judging the lay of land, picked my spot and set the Trimble to gather data.  Once the Trimble had been activated I headed to the nearby hedge and sat in the field below it and next to a particularly dense covering of hedgey stuff.  Within a couple of minutes the rumbles of a vehicle from the farm came up the lane, oh gawd, imagine trying to explain what I was doing.  I waited for it to pass and then hoped it wouldn’t turn right, as if it did I would be in full view of the occupant as they passed the fence I had clambered over.  Thankfully they turned left and headed up the lane toward the summit of the hill.  Once five minutes of data had been collected I quickly got back on to the lane and walked up the road to a gate just over the crest of the hill, which gave access to the summit field.

Gathering data at the bwlch with the Llyn Clywedog dam in the background
Looking up the lane toward the summit
Three data sets were collected, one from what I judged to be the high point, one from the high point near to the road and the third from the high point of an earthen embankment that ran parallel to the road.  In all fifteen minutes of data was collected from these points and the same probably spent setting the equipment up, and all spent with me wandering around in a field, next to a road, hoping that no farmer’s vehicle would turn up.  The only one I could see was a quad bike on a lower field; I tried to keep out of his line of sight.

The Trimble GeoXH 6000 gathering data at the second point on the summit area, the high point of the hill is on the left
By 10.55am I was back at the car and travelling toward Llanidloes and then Welshpool.  Soon after arriving home the predicted rain arrived.  A great morning, only done because I’d mistakenly visited the lower top of Dinas two days previously, so I had to re-visit to get high point summit data.   



Survey Result:


Pt. 318.8m

Summit Height:  318.8m (converted to OSGM15)

Summit Grid Reference:  SN 92423 85349

Bwlch Height:  289.1m (converted to OSGM15)

Bwlch Grid Reference:  SN 92032 85614

Drop:  29.8m (300m Sub-Trichant status confirmed)

Dominance:  9.33%



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

Wednesday, 23 April 2014

Mapping Mountains – Trimble Surveys – Pumlumon


20.04.14  Pt. 381.7m (SN 926 875)


Pt. 381.7m (SN 926 875)
After venturing back up to Dinas (SN 904 885) and visiting the proper summit I drove east, past Llyn Clywedog and parked on the grass verge at SN 923 875 adjacent to the bwlch of a 382m summit that is unnamed on the map.  I inspected the area of the bwlch many a year ago with Rob Woodall whilst visiting three hills with him; our conclusion was that the hill has approximately c 31m of drop.

It only took a few minutes to judge the bwlch and having decided on the spot to place the Trimble I set it up and waited for it to attain the 0.1m accuracy before data can be logged.  This only took a minute or so, and when it was doing its stuff I happily peered through the gloom toward Bryn y Fan (SN 931 884) across the intervening valley.


Not far from the car to the bwlch for this hill.
Once five minutes of data had been gathered at the bwlch I packed the Trimble away and walked up to the summit.  The only name that appears on the map associated with this hill is either ‘fort’ or ‘hill camp’, and as one can imagine it has the remains of an ancient hill fort on the summit area.

The highest point is easily identifiable and within a few minutes the Trimble was on it gathering its customary ten minutes of summit data, when this was happening I took a few photos and admired the bulk of Bryn y Fan as it shot up in to the sky line across the valley.


The Trimble GeoXH 6000 on the summit gathering data
45 minutes after leaving the car I was back at it, studying the map as I wanted to investigate one more potential new P30 before the predicted afternoon’s rain arrived. 



Survey Result:


Pt. 381.7m

Summit Height:  381.7m (converted to OSGM15)

Summit Grid Reference:  SN 92639 87499

Bwlch Height:  350.1m (converted to OSGM15)

Bwlch Grid Reference:  SN 92434 87526

Drop:  31.6m (Trichant status confirmed)

Dominance:  8.28%



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

Tuesday, 22 April 2014

Mapping Mountains - Hill Reclassifications – Y Pedwarau


Carreg y Big (SN 902 909) - 400m Sub-Pedwar deletion

There has been a deletion of a 400m Sub-Pedwar by surveying with the Trimble.  The hill was only listed in this sub category as it has a 394m spot height at the bwlch and a 417m spot height at the summit on the Ordnance Survey enlarged mapping hosted on the Geograph website, with these values giving this hill a drop of 23m.  The spot height at the bwlch on the OS map is on a road, and the position of the critical bwlch is higher than this .  The name of the hill is Carreg y Big (SN 902 909) and is situated in the Pumlumon range.

The hill will be deleted from the Y Pedwarau list in the 2nd edition that will be hopefully be published by Europeaklist.  The list of Pedwar hills is also available from the Haroldstreet website.


The full details for the hill are:



Cardinal Hill:  Foel Fadian

Summit Height:  417.0m (converted to OSGM15)

Name:  Carreg y Big

OS 1:50,000 map:  136

Summit Grid Reference:  SN 902 909

Drop:  19.7m (converted to OSGM15)



The Trimble GeoXH 6000 on the summit of Carreg y Big
For details on the survey that deleted this hill from 400m Sub-Pedwar status please click {here}



Myrddyn Phillips and Aled Williams (April 2014)

Monday, 21 April 2014

Hill Lists – Cymru / Wales – 200m Twmpau updates – Moel Hebog



The first list to the Welsh 200m P30 hills was published on Geoff Crowder’s website v-g.me in 2000; this list preceded the list of TuMPs by nine years, the list proved a very useful resource for the TuMP compilation for this category of hill.

The Welsh 200m P30 list documents all hills in Wales that are at or above 200m in height and are below 300m in height, to qualify for the main list each hill requires a minimum of 30m of prominence.

The hills listed below are updates to the Welsh 200m P30 list originally published on Geoff Crowder's website.  To see the original list click {here}

The original published list had a Sub-List which was entitled ‘Hills to Survey’.  This list consisted of all hills in Wales in the stipulated height band that have a minimum of 20m of prominence, but do not meet the minimum 30m of prominence to enter the main list, according to Ordnance Survey map spot heights and contours.  Nowadays the standard Sub-List takes in all hills that have a minimum of 20m of prominence.  However, the Hills to Survey Sub-List discounted hills whose map spot heights gave a drop value of less than 30m, but more than 20m.  By doing so, the only hills that were Sub-Listed were those that map values dictated stood a chance of entering the main list, for example; if a hill had a summit spot height of 250m and a bwlch spot height of 221m, it was not listed in the Hills to Survey Sub-List as with 29m of drop I thought it did not stand a chance of main list qualification. 

When compiling the Sub-List I was measuring many hills for P30 status using a basic levelling technique, please click {here} for more information concerning this.  I now know that Ordnance Survey spot heights have a standard margin of uncertainty of + / - 3m associated with their accuracy.  Therefore many hills that were not listed in the original Sub-List may have sufficient drop to enter the main list.  Because of this the Sub-List has been altered to include all hills that have a minimum of 20m of drop but are not known to attain the minimum 30m of drop to enter the main list.

The hills listed below are those major amendments to the original Welsh 200m P30 list as it appears on Geoff’s website.  There are many hills that have been promoted from the Hills to Survey Sub-List to the main list, whilst there are many additions to the Sub-List now that it has been standardised to include all 20m minimum but below 30m drop hills.

When the 200m P30 list was first published it was the first to this category of hills and in some way it and its other 100m height band lists paved the way for Clem’s data that later appeared on the RHB file database and then for the TuMPs listing by Mark Jackson.

As well as the first P30 list to this height band the list is now the first to include a comprehensive Sub-List.

TuMP baggers beware; as the main list also includes P30’s not listed by Mark Jackson, so if you want to visit all P30’s you’ll have to include some non TuMPs to do so.


The list will be updated on a weekly basis and will be done so through each Group category, starting from the north and working south.  The second Group that has major updates is Moel Hebog.


Moel Hebog

North of Aberdesach at SH 425 514 continuing north of the Afon Desach and east of the Afon Dwyfach (centred on SH 453 485) to SH 478 372, west of the Afon Glaslyn at SH 582 380 / Afon Colwyn to bwlch at SH 576 514, continuing to Llyn y Gadair (SH 568 521) and the Afon Gwyrfai to Foryd Bay (SH 454 591).  Bordering with Yr Wyddfa to the north, Pen Llŷn to the west and the Moelwynion to the east.



Twmpau - 200m updates

Moel Isallt    286m    SH 537 445

Another hill that was always a prime candidate for promotion from the sub-list and with the large scale Ordnance Survey mapping on the Geograph website giving a 252m spot height on the area of the bwlch it gives this hill 34m of drop.


Moelfryn    277m    SH 568 511

With a summit height of 277m and bwlch contouring between c 240m – c 250m, with the hill to hill contouring being relatively close when compared to the valley to valley contouring, this hill was always a prime candidate for promotion from the sub-list and with an estimated bwlch height of c 247m, it enters the list with c 30m of drop.



Sub-Twmpau - 200m updates

Bryn Cwellyn    c 272m    SH 564 536

A forested summit near to Llyn-y-forwyn which has an estimated summit height of c 272m (a separate point at SH 56454 53329 is estimated as c 271m) and an estimated height at Bwlch y Moch (SH 561 540) of c 252m, giving a drop of c 20m.


Craig Isallt    233m    SH 532 449

With a summit height of 233m and an estimated bwlch height of c 213m, this hill just makes it in to the sub-list with c 20m of drop.



Next update due on the 28st April 2014

Sunday, 20 April 2014

Mapping Mountains - Hill Reclassifications – 300m Twmpau



Mynydd Derw Llwydion (SO 907 900) - 300m Sub-Twmpau reclassified to 300m Twmpau

There has been a new addition to the 300m Twmpau list due to a recent survey with the Trimble GeoXH 6000.  The hill sneaks in with 14 millimetres to spare!  This margin is within the uncertainty applied to the equipment and its positioning at the summit and the bwlch.  However, reclassifications are taking place in the listings I have compiled and those jointly done with Aled Williams, from best available evidence on the day and as this hill used to be listed with 29m of drop based on Ordnance Survey summit and bwlch spot heights, the Trimble data will be more accurate.  So until better evidence is produced the hill is promoted from the 300m Sub-Twmpau list and becomes a new P30.  The hill is situated in the Pumlumon range amongst many P30s between Llyn Clywedog and Penffordd-las (Staylittle).


The full details for the hill are:


Cardinal Hill:  Foel Fadian

Summit Height:  388.1m (converted to OSGM15)

Name:  Mynydd Derw Llwydion

OS 1:50,000 map:  136

Summit Grid Reference:  SN 90721 90069

Drop:  30.0m (converted to OSGM15)


The Trimble GeoXH 6000 on the summit of Mynydd Derw Llwydion, which is now reclassified to a 300m Twmpau

For details on the survey that reclassified this hill to 300m Twmpau status please click {here}


Myrddyn Phillips (April 2014)

Saturday, 19 April 2014

Mapping Mountains – Trimble Surveys – Pumlumon


18.04.14 and 20.04.14  Bryn y Tail (SN 916 874), Waun y Gadair (SN 918 887), Dinas (SN

904 885), Mynydd Derw Llwydion (SN 907 900), Foel Fawr (SN 900 904), 

Carreg y Big (SN 902 909), Mynydd Dyrnol (SN 901 917) and Gamallt (SN 895 925)


Yr Allt (SN 908 875)
Pedwar bagging, and a walk I’d wanted to do for a number of years, but as many of the hills are not dramatic and are no more than high grassy fields, albeit quite lovely high grassy fields, and as I guessed that there would be a number of barbed wire fences to negotiate and non-access land to venture on to, I wondered if it was appropriate to do the walk with another person.  Having now got the Trimble and wanting to survey the eight summits and eight bylchau en route it was definitely a walk to do on my own.  I remember John Fitzgerald (pioneer of Trimble mountain surveys) saying that he was finding some of his hill walking friends were mysteriously disappearing and no longer visiting the hills with him as they didn’t want to stop every few minutes and wait whilst he gathered another data set.  I’ll have to be aware of this, especially so on walks that include a number of summits.  After all there seems to be only a select few hardened surveying souls who are willing to twiddle their respective fingers time after time; Barnard, Jackson, Trengove and Williams to name but four are ones that swing to mind.

I parked in the car park adjacent to the Llyn Clywedog dam (SN 921 881) at 8.40am and was soon standing beside the road with a small sign saying ‘Staylittle Please’ on one side and ‘Three Miles Please’ on the other.  The intention being to hitch to Staylittle and walk back over the hills to the Clywedog dam, half an hour later only about ten cars had passed and none had stopped.  Therefore I drove to Staylittle, parked and smiled at a woman who was walking up the lane to her car, within a few minutes I was happily sitting in her and her husband’s motor home heading back down the road to the Clywedog dam.  They were on their way to mainland Europe for a week travelling around.  I thanked them as I was dropped off at the top of the road above Llyn Clywedog, next to a gate and stile that gave easy access to the first hill of the day.

It was just past 9.35am as I made my way up toward the summit of Bryn y Tail, the hill didn’t live up to its name (the manure hill or the dung hill) as there wasn’t a cow pat in sight.  The last upper section is on a small, broad grassy ridge; I placed the Trimble on the high point and gathered the customary ten minutes of data.  Bryn y Fan dominated the view to the north-east, with Dinas (the third hill of the day) dominating the north-western view across the waters of Llyn Clywedog.


The Trimble GeoXH 6000 on the summit of Bryn y Tail (SN 916 874) with Bryn y Fan (SN 931 884) in the background
Bryn y Tail (SN 916 874)
The northerly ridge down toward the dam is a delight; soon it brought me to a gate and access on to the road and the dam.  I wanted to investigate the land below the dam on its eastern side and see if any remnants of the natural bwlch still remained, before doing so I gathered five minutes of data from the stone parapet of the dam wall and input a 1.03m height offset in to the Trimble. 


Gathering data on the stone parapet of the dam at Bwlch y Gle
The Reservoir was completed in 1967 and dammed the Afon Clywedog; a tributary of the Afon Hafren (River Severn), its concrete dam wall is the tallest of its kind in the UK with a height of 72m and a length of 230 metres.  The catchment water supplies Birmingham and the English midlands.  When looking on Ordnance Survey maps that pre-date 1967 the Afon Clywedog contours its way around Dinas, the finger of north-easterly land delicately descending from the summit of Yr Allt and the southerly land of Bryn y Tail before heading south-east to join the Afon Hafren at Llanidloes.  These old maps also give the area of land where the natural bwlch once lay.  It was this that I now wanted to go and look for.

Just below the dam road is a path / track that makes its way toward the summit of Bryn y Fan, this path is also on the hill to hill traverse between Bryn y Tail and Waun y Gadair.  I placed the Trimble on a suitable spot and gathered another five minutes of data.  It was very hard to judge if the natural bwlch still remained; it could well be buried under the road or the waters of the reservoir.  However the processed data will at least give us an accurate height for the ground below the road and this can then be compared to the contours on old maps.


Is this the natural critical bwlch for Bryn y Tail?
By now I’d taken my one skin summer walking jacket off as the slight chill of the morning had been replaced by the strengthening heat of the sun.  The next hill was Waun y Gadair (SN 918 887); a Pedwar with a listed drop of 39m.  Once summit data was collected I spent quite some time getting data from a number of points to see which the true critical bwlch was.  Altogether five points were surveyed, some beside the road, which proved rather daunting considering the last time I did this a car ran over the Trimble, this time it was placed a metre or so from the road and I stood near to it, facing oncoming traffic, so cars had to pass me first.


Waun y Gadair (SN 918 887)
Dicing with Trimble death, one of the five points surveyed for the critical bwlch position of Waun y Gadair
The continuation toward Staylittle was via Dinas (SN 904 885), another Pedwar, and one that had a grassed vehicle track making its way up toward the summit, the high point overlooks the blue waters of Clywedog.  Once summit data had been collected I retraced my steps and joined the road to survey the critical bwlch for Dinas.


Dinas (SN 904 885)
Or so I thought, that is, as far as visiting the summit of Dinas is concerned, having processed the data the day after the visit I found out that I only got as far as a small subsidiary summit a few hundred metres from the higher top - oooppppssss.  So I revisited early in the morning on the 20th in slightly different conditions, as it was mightily chilly, murky and with wisps of mist passing over the summit.  At least I got some summit data this time!  Right the interlude is over, on with the blog post about the walk..............



The Trimble GeoXH 6000 on the subsidiary summit of Dinas (must remember to check the map next time)
Early morning and now back at the higher summit which can be seen in the background in the above photo
My route now took me away from the B4518 as I headed north up a minor road to the summit of a 387m map heighted hill at SN 907 900 which is listed as Mynydd Derw Llwydion as the land where the summit of this hill is situated is on the sheepwalk of the farm named Derw Llwydion.  As the Trimble gathered data atop the grassy top I stood and watched a Red Kite majestically pass overhead with a radiant blue as a backdrop.  This hill is listed as a Sub with 29m of drop in the Welsh 300m P30 list, the drop figure based on the 387m summit spot height and a 358m spot height at SN 903 902 that appears on a road junction on OS maps.  The critical bwlch proved to be higher than the road junction and just to its north-east.

Such a majestic bird - Red Kite
Summits and bylchau were now appearing in quick succession, with the summit of Foel Fawr (SN 900 904) being another attractive high point atop a rock outcrop.  The next bwlch was in a bog (SN 900 906) which thankfully had dried somewhat due to the sunshine over the last week, whilst collecting data a well camouflaged hare scampered off, I hoped it wasn’t on a collision course with the Trimble as it was heading that way!  The following summit was Carreg y Big (SN 902 909) a Sub-Pedwar with 23m of listed drop based on 417m summit and 394m bwlch spot heights, the bog at the bwlch was higher and to the west of where the 394m spot height appears on the map, doubtful that it’ll loose its Sub-Pedwar status though.


The summit of Foel Fawr (SN 900 904)
The next bwlch (SN 901 913) has a 379m spot height on a road junction on OS maps, when I reached this point I looked, and looked, and did a bit more looking and approached the area from various angles and still ended up not knowing where on earth to place the Trimble.  I think the heat had caused a serious case of bwlch mind muddle!  The path of the bwlch seemed to curve its way around the central grass and gravel triangle that separated the roads and then it seemed to curve its way back.  I gave the margin of uncertainty applied to the Trimble position as 0.5m, placed it next to the road and hoped a car would not try and kill it again.  I think it was on a safe bet as no car had passed on this minor road for at least half an hour.


Bwlch mind muddle, such a small area of land, but I just could not work out where the Trimble should be placed
Only two summits remained and the next was Mynydd Dyrnol (SN901 917) another Sub-Pedwar with a 28m listed drop.  The summit area was quite expansive when compared to previous ones of the day; I picked my spot, logged ten minutes of data and proceeded down to another bog which is next to a raised stone track and the bwlch of the hill.


All that remained was the slow plod up to the highest summit of the day; Gamallt (SN 895 925).  The high point is a few metres away from a fence junction that has an unusual pillar next to it.  The last and 21st data point (a record for me, beating the 16 data points taken on the walk around the Breiddin on 18.12.13) of the day was beside a fence separating rough ground from furrowed land that beyond comprised a conifer plantation.  After five minutes of data from the point, which is the critical bwlch for Gamallt, was collected, I joined a track that swings around the hill and down in to Staylittle.  A great day, eight hills, eight bylchau, 21 data points taking over eight hours, these hills are seldom visited and are situated in beautiful land overlooking Llyn Clywedog and the wilds of the high Pumlumon range to their west, a good little ridge walk, albeit a bit convoluted.


The summit of Gamallt (SN895 925)


Survey Result:



Bryn y Tail

Summit Height:  403.1m (converted to OSGM15) (Pedwar status confirmed)

Summit Grid Reference:  SN 91690 87470

Bwlch Height:  277.5m (converted to OSGM15) (ground below road passing over dam)

Bwlch Grid Reference:  SN 92150 88255 (ground below road passing over dam)

Drop:  125.6m

Dominance:  31.16%


The Ordnance Survey Historical 1:25,000 map has bwlch contouring between 925ft – 950ft (282m –290m).  As the height of the ground below the dam is 277.5m (converted to OSGM15) it indicates that the natural bwlch no longer exists.  However, the ground surveyed with the Trimble below the dam is likely to be closer in position and height than any other feature still remaining, therefore these details are taken for the bwlch of this hill.  

Post detailing the later survey beside the water in the Reservoir



Waun y Gadair

Summit Height:  403.8m (converted to OSGM15) (Pedwar status confirmed)

Summit Grid Reference:  SN 91823 88721

Bwlch Height:  367.0m (converted to OSGM15)

Bwlch Grid Reference:  SN 91460 88895

Drop:  36.8m

Dominance:  9.12%



Dinas

Summit Height:  445.3m (converted to OSGM15)

Summit Grid Reference:  SN 90409 88538

Bwlch Height:  342.9m (converted to OSGM15)

Bwlch Grid Reference:  SN 90377 89417

Drop:  102.4m (Hump status confirmed)

Dominance:  23.00%



Mynydd Derw Llwydion

Summit Height:  388.1m (converted to OSGM15)

Summit Grid Reference:  SN 90721 90069

Bwlch Height:  358.1m (converted to OSGM15)

Bwlch Grid Reference:  SN 90391 90264

Drop:  30.0m (Trichant addition confirmed)

Doninance:  7.73%   




Summit Height:  422.9m (converted to OSGM15)

Summit Grid Reference:  SN 90029 90416

Bwlch Height:  378.8m (converted to OSGM15)

Bwlch Grid Reference:  SN 90119 91400

Drop:  44.1m

Dominance:  10.43%



Carreg y Big

Summit Height:  417.0m (converted to OSGM15)

Summit Grid Reference:  SN 90241 90949

Bwlch Height:  397.3m (converted to OSGM15)

Bwlch Grid Reference:  SN 90124 90659

Drop:  19.7m (400m Sub-Pedwar deletion confirmed)

Dominance:  4.72%



Mynydd Dyrnol

Summit Height:  412.0m (converted to OSGM15)

Summit Grid Reference:  SN 90242 91672

Bwlch Height:  383.0m (converted to OSGM15)

Bwlch Grid Reference:  SN 90145 91971

Drop:  28.9m (400m Sub-Pedwar status confirmed)

Dominance:  7.02%



Gamallt

Summit Height:  450.8m (converted to OSGM15)

Summit Grid Reference:  SN 89552 92558

Bwlch Height:  415.0m (converted to OSGM15)

Bwlch Grid Reference:  SN 89529 92861

Drop:  35.8m (Pedwar status confirmed)

Dominance:  7.94%



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