Mapping Mountains – Hill Reclassifications – Y Pedwarau - The 400m Hills of Wales

Moelfre (SH 717 744) - 400m Sub-Pedwar deletion

There has been a deletion of a 400m Sub-Pedwar by analysis of LIDAR data coupled with a previous survey with the Trimble GeoXH 6000.  The hill continued to be listed as a 400m Sub-Pedwar based on a 433.0m (converted to OSGM15) surveyed summit height and an on-site visual inspection of one of two potential positions for this hill’s critical bwlch, this option for the bwlch position was considered lower than the second option for the bwlch position at SH 71909 74471 which was surveyed as being 416.9m (converted to OSGM15) high.  Because of this the hill was retained as a 400m Sub-Pedwar with an estimated drop of c 20m.  The 400m Sub-Pedwarau are the Welsh hills at or above 400m and below 500m in height with a drop between 20m and below 30m.

LIDAR image of Moelfre (SH 717 744)

The hill is positioned above the towns of Penmaenmawr to its north and Llanfairfechan to its west and can be easily accessed from a green track that continues from the end of a minor lane to the hill’s west, or from its north-west where public footpaths and bridleways lead close to its summit. 

The hill’s summit and one prospective position for its bwlch was surveyed in the late evening with Aled Williams and the hill is positioned in the northern Carneddau in north-west Wales.  This hill range comprises some of the highest mountains in the country but the evening walk concentrated on some of its 300m and 400m lower hills.

The name of the hill is Moelfre and prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 435m.  This height appears on the Ordnance Survey 1:25,000 Explorer and 1:50,000 Landranger maps and the Ordnance Survey enlarged map on the Geograph website.  This 435m height seems to be a recent addition as the series of Ordnance Survey Six-Inch maps from 1888 - 1946 have a 1,422ft (433.4m) height, whilst the Ordnance Survey Seventh Series One-Inch map and the Historical 1:25,000 map has 1,423ft (433.7m).

Moelfre was surveyed with the Trimble GeoXH 6000 as being 433.0m (converted to OSGM15) high and one of its two bwlch positional options at SH 71909 74471 was surveyed as being 416.9m (converted to OSGM15) high, with the second bwlch positional option at SH 72253 74153 estimated as being c 413m high, which gave this hill c 20m of drop and therefore it retained its status as a 400m Sub-Pedwar.

However, since the survey with the Trimble, Aled has analysed the bwlch position via LIDAR data, whose height we had previously estimated from a visual inspection.  LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales.  Analysing LIDAR data gave the following result:

Summit Height:  433.2m

Summit Grid Reference:  SH 71735 74416

Bwlch Height:  414.7m

Bwlch Grid Reference:  SH 72254 74153

Drop:  18.5m

The summit data produced by LIDAR is comparable to that produced by the Trimble GeoXH 6000, these are detailed below:

433.2m LIDAR summit height at SH 71735 74416

433.0m (converted to OSGM15) Trimble summit height at SH 71733 74418

Therefore, the 414.7m LIDAR data produced for the bwlch position at SH 72254 74153 that had previously been visually inspected is considered accurate and when coupled with the 433.0m (converted to OSGM15) summit height produced by the Trimble GeoXH 6000 gives this hill 18.3m of drop, which is insufficient for the hill to retain its 400m Sub-Pedwar status, and therefore Moelfre is deleted from the listing of 400m Sub-Pedwar hills and the list of the Y Pedwarau will be updated accordingly.  The list of Pedwar hills is available from the Haroldstreet website.

The full details for the hill are:

Cardinal Hill:  Tal y Fan

Summit Height:  433.0m (converted to OSGM15)

Name:  Moelfre

OS 1:50,000 map:  115

Summit Grid Reference:  SH 71733 74418 

Drop:  18.3m (Trimble summit and LIDAR bwlch)

The list of additions, reclassifications and deletions from the 400m Sub-Pedwar list since the 1^st edition of the Y Pedwarau was published by Europeaklist are as follows:

400m SUB-PEDWAR ADDITIONS

Pt. 452.4m (converted to OSGM15) (SJ 229 443) 22.6m drop

Bryn Glas (SH 735 420) 21.7m drop

Derlwyn (SH 588 586) 20.4m drop

Pt. 422.3m (converted to OSGM15) (SO 073 822) Pedwar reclassified to 400m Sub-Pedwar with 29.0m drop

Wenallt (SN 933 571) Pedwar reclassified to 400m Sub-Pedwar with 28.3m drop

Bryn Serth (SO 147 109) Pedwar reclassified to 400m Sub-Pedwar with 25.4m drop

Banc Bronderwgoed (SN 871 987) Pedwar reclassified to 400m Sub-Pedwar with 27.7m drop

Drysgol (SN 946 744) Pedwar reclassified to 400m Sub-Pedwar with 29.2m drop

Craig y Garreg-lwyd (SH 730 427) Pedwar reclassified to 400m Sub-Pedwar with 29.9m drop

Pt. 407.7m (converted to OSGM15) (SO 180 692) Pedwar reclassified to 400m Sub-Pedwar with 28.3m drop

400m SUB-PEDWAR RECLASSIFICATIONS

Y Garn (SH 758 375) 400m Sub-Pedwar reclassified to Pedwar with 31.2m drop

Cefn Perfa (SO 173 579) 400m Sub-Pedwar reclassified to Pedwar with 30.1m drop

Craig y Ganllwyd (SH 707 258) 400m Sub-Pedwar reclassified to Pedwar with 33.4m drop

Pt. 499.5m (converted to OSGM15) (SH 665 310) 400m Sub-Pedwar reclassified to Pedwar with 30.3m drop

Mynydd Poeth (SH 953 513) 400m Sub-Pedwar reclassified to Pedwar with 31.7m drop

400m SUB-PEDWAR DELETIONS

Moelfre (SO 121 759) 19.8m drop

Carreg y Big (SN 902 909) 19.7m drop

Foelas Fechan (SH 854 596) 18.6m drop

Moelfre (bwlch LIDAR data) (SH 717 744) 18.3m drop

Moelfre (SH 717 744) the deleted 400m Sub-Pedwar

For details on the survey that when coupled with analysis of LIDAR data deleted Moelfre from 400m Sub-Pedwar status

Myrddyn Phillips and Aled Williams (December 2016)

Mapping Mountains – Significant Height Revisions – Y Pedwarau - The 400m Hills of Wales

Moelfre (SH 717 744)

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill listed in the Y Pedwarau, and which was subsequently confirmed by LIDAR analysis conducted by Aled Williams, with the survey that resulted in this height revision being conducted on the 4^th July 2016.

LIDAR image of Moelfre (SH 717 744)

The criteria for the listing that this height revision affects are:

Y Pedwarau - Welsh hills at and above 400m and below 500m in height that have 30m minimum drop.

400m Sub- Pedwarau - Welsh hills at and above 400m and below 500m in height that have 20m or more and below 30m of drop.

The name of the hill is Moelfre and it is situated in the Carneddau range of hills which are in north-west Wales.  This hill range comprises some of the highest mountains in the country but the evening walk when the survey was conducted concentrated on some of its 300m and 400m lower hills.

Moelfre is positioned above the towns of Penmaenmawr which is to its north and Llanfairfechan which is to its west and it can be easily accessed from a green track that continues from the end of a minor lane to the hill’s west, or from its north-west where public footpaths and bridleways lead close to its summit.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 435m, with this height taken from the Ordnance Survey 1:50,000 Landranger map, Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey enlarged mapping hosted on the Geograph website.  The 435m height seems to be a recent addition as the series of Ordnance Survey Six-Inch maps from 1888 - 1946 have a 1,422ft (433.4m) height, whilst the Ordnance Survey Seventh Series One-Inch map and the Historical 1:25,000 map has 1,423ft (433.7m).

Moelfre was surveyed with the Trimble GeoXH as being 433.0m (converted to OSGM15) high.  This is not a dramatic height revision when compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.

The summit of the hill is easily identified and consists of an ancient cairn that is now an oval mound, with the centre of the mound being slightly hollowed, and therefore this hill’s new summit height as surveyed by the Trimble GeoXH 6000 is 433.0m (converted to OSGM15) which is 2.0m lower than its previously listed height of 435m which appears on the Ordnance Survey enlarged mapping hosted on the Geograph website and the 1:25,000 Explorer and 1:50,000 Landranger maps.

The full details for the hill are:

Cardinal Hill:  Tal y Fan

Summit Height:  433.0m (converted to OSGM15)

Name:  Moelfre

OS 1:50,000 map:  115

Summit Grid Reference:  SH 71733 74418

Drop:  18.3m (Trimble summit and LIDAR bwlch)

The Trimble GeoXH 6000 gathering data at the summit of Moelfre (SH 717 744) which resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips and Aled Williams (August 2016)

Mapping Mountains – Trimble Surveys – Carnedd Llywelyn

14.07.16  Penmaen Mawr (SH 698 755), Penmaen Mawr (SH 702 756), Clip yr Orsedd (SH 711 747) and Moelfre (SH 717 744)

Penmaen Mawr (SH 698 755)

When seen from the A 55 the northern aspect of Penmaen Mawr rises in scree laden slopes to what was once a proud and prominent hill.  This hill has now been quarried and where a 1,550ft (472m) map heighted summit once was, there is now a gaping hole.  Quarrying this hill also destroyed an ancient hill fort that encircled the summit.  In its time Penmaen Mawr would have been an impressive hill as along with its ancient hill fort it was prominent above its surrounding lands as the bwlch that connected this hill to its adjacent neighbour of Clip yr Orsedd is, according to current maps, between 360m – 370m in height, giving the old hill over 100m of prominence.

Destroying the hill has meant that Penmaen Mawr can no longer be considered for Hump (HUndred Metre Prominence) status, and that its Pedwar (Welsh 400m hills) status has long gone with the last stick of dynamite used to blow the summit area to bits.  However, no accurate summit height is known for what remains of the hill and it had long been a priority to survey.

I met Aled at 5.00pm in Dwygyfylchi where we left his van and continued in my car to our parking spot high on a minor road above Llanfairfechan.  It was only a short walk up a track to the bwlch connecting Penmaen Mawr with Clip yr Orsedd, and when we arrived it was relatively easy to pinpoint its critical position.

As the Trimble gathered five minutes of data we chatted with a man who was out for an evening walk, and once the data set was complete I packed the equipment away and started up the gravelled slopes of quarried debris toward the first high point of what remains of the hill.

Gathering data at the critical bwlch of the two Penmaen Mawr summits

This first high point was no more than a mound of quarry debris and we had both spotted it when driving on the A 55 earlier in the day as it rises steeply and is pronounced.  Remarkably it was relatively stable when we climbed up it.  As the Trimble gathered data I stood immediately below it whilst Aled wandered over to look down into the gaping hole of the quarry.  Dotted about where remains of ancient and relatively modern habitation with the lower rock walls of ancient round huts still to be found, whilst the old quarry had its own more modern buildings, many now dilapidated and left to nature’s way.

Aled with the lower of the two Penmaen Mawr summits in the background

Over recent days Aled had scrutinised this hill via photographs and maps and realised that the easterly point of what remains of the hill may have sufficient prominence to be classified as a Sub or even a P30, and therefore after making our way over to the remaining natural high point and Trimbling it we headed down to the connecting land between the westerly and easterly high points, this proved to be on a steep mound of gravel beside long grasses and nettles, it too was also Trimbled.

Gathering data from the higher of the two Pernmaen Mawr summits

Heading toward the bwlch connecting the summit of Penmaen Mawr with the lower easterly summit

What remains of the hill on what is now its easterly high point is impressive as the quarry has gauged the upper hill into a cliff which gave us a little hands on rock excitement, once on its ridge the view down the coast toward Gogarth and Llandudno sprang into view.  The ridge was fun and gave us a small scramble of sorts with the drop to our right increasing as height was gained.

The southern face of the lower of the two Penmaen Mawr summits consists of an impressive looking rock face

Since the survey with the Trimble GeoXH 6000 Aled has analysed LIDAR data and the high point of the hill is not where data was gathered from and therefore the details given later in this post are those taken from LIDAR data.  When we reached what we thought to be the high point I set the Trimble on a large rock which was immediately above a gaping drop, not wanting to lose the Trimble to an early death I set it up on its dog lead, aligned its internal antenna with the highest part of the rock and sat below it with the lead fixed to the Trimble and securely around my wrist for the five minutes of data collected.

Heading toward the lower of the two Penmaern Mawr hills

Gathering data on the lower of the two Penmaen Mawr hills

The view east toward the shapely Foel Lus

As we headed down to the track where the first data set for the bwlch for Penmaen Mawr had been gathered, there was also an alternate connecting bwlch for the easterly high point to survey, this we thought to be on a track and connected the easterly high point to the higher Penmaen Mawr.

Gathering data at the area of the bwlch of the lower of the two Penmaen Mawr summits

However, the surveying of Penmaen Mawr had not ended as there was also an alternate bwlch position to survey for the high point of the hill, and this was on the way up towards our next hill; Clip yr Orsedd.  Once five minutes of data were gathered from this point we walked up to the summit of Clip yr Orsedd as the sun disappeared into a milky sky.

Our original plan was to do a two car walk and continue as far as Foel Lus, a 362m map heighted hill at SH 732 761, but we’d already conducted eight surveys and been on the hill for three hours, and if we continued toward Foel Lus in all likelihood we’d be descending a steep hill in darkness, therefore we quickly revised our plan and decided to continue to Moelfre and descend the green track on the southern side of Clip yr Orsedd straight back to my awaiting car.

Gathering data at the summit of Clip yr Orsedd

By now an evening’s chill had set in and the slow ebb of dusk was gathering.  Beyond the summit of Clip yr Orsedd we joined a path heading down toward its connecting bwlch with Moelfre, we assessed the lay of land and decided that the critical point was beside the track which crosses a reed invested bog, once five minutes of data were gathered we wandered up the steep northern slopes of Moelfre.

This hill has two potential positions for its critical bwlch and time dictated that only one could be surveyed, so after a five minute data set was collected at the summit I set the Trimble up at the neatest bwlch position and Aled wandered off in the direction of Tal y Fan to inspect the other bwlch option.  The bwlch nearest to Tal y Fan looked decidedly lower, and although a visual inspection is not ideal as the human eye can have difficulty judging hill heights, it did at least give us inkling which was lower and therefore the position of the critical bwlch of Moelfre.

Gathering data at the summit of Moelfre

As the Trimble gathered the last of its 300 data points, Aled re-appeared and said that the bwlch nearest to Tal y Fan looked at least 3m lower than where the Trimble was now gathering data, this was important as this hill is currently listed as a Sub-Pedwar with a drop of c 21m, so the position and height of its critical bwlch is all important.

After packing the Trimble away we walked down to the green track and followed it in dimming light arriving back at my car at 9.50pm.

LIDAR image of Clip yr Orsedd (SH 711 747)

LIDAR – Postscript 

Since visiting these hills full LIDAR coverage is now available.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height and positional data that is now freely available for England and Wales.  Consequently the numerical details for these hills have been analysed using this technique, resulting in the LIDAR height and position being prioritised for some of these hills.

Survey Result:

Penmaen Mawr

Summit Height:  390.4m (converted to OSGM15) (significant height revision and 390m Double Sub-Pedwar addition confirmed)

Summit Grid Reference:  SH 69865 75523

Bwlch Height:  363.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 70332 75118

Drop:  26.9m (390m Double Sub-Pedwar addition confirmed and Sub-Trichant addition confirmed)

Dominance:  6.90% 

 

Penmaen Mawr

Summit Height:  385.8m (LIDAR) (significant height revision)

Summit Grid Reference:  SH 70292 75649 (LIDAR)

Bwlch Height:  354.5m (LIDAR)

Bwlch Grid Reference:  SH 70441 75241 (LIDAR)

Drop:  31.3m (LIDAR) (Trichant addition)

Dominance:  8.11% (LIDAR)

  

Clip yr Orsedd

Summit Height:  426.6m (converted to OSGM15, Trimble GeoXH 6000) (significant height revision)

Summit Grid Reference:  SH 71185 74743 (Trimble GeoXH 6000)

Bwlch Height:  387.5m (LIDAR)

Bwlch Grid Reference:  SH 71805 74672 (LIDAR)

Drop:  39.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  9.19% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Moelfre

Summit Height:  433.0m (converted to OSGM15, Trimble GeoXH 6000) (significant height revision)

Summit Grid Reference:  SH 71733 74418 (Trimble GeoXH 6000)

Bwlch Height:  414.7m (LIDAR)

Bwlch Grid Reference:  SH 72254 74153 (LIDAR)

Drop:  18.3 (Trimble GeoXH 6000 summit and LIDAR bwlch) (400m Sub-Pedwar deletion) 

Dominance:  4.23% (Trimble GeoXH 6000 summit and LIDAR bwlch)

For further details please consult the Trimble Survey Spreadsheet.