Mapping Mountains – Trimble Surveys – Cadair Idris

10.05.18  Castell y Bere (SH 667 085), Foel Cae’rberllan (SH 676 082), Foel Ddu (SH 697 095), Mynydd Ty’n y Fach (SH 687 097) and Craig Ysgiog (SH 684 102)

Foel Ddu (SH 697 095)

Having recently LIDARed this area I thought I had better visit, and with the weather set fine I headed to the upper Dyffryn Dysynni, a beautiful part of the country and one that I had not visited for a number of years.

LIDAR image of Foel Cae'rberllan

On my surveying agenda were two great lumps of hills; Foel Cae’rberllan and Foel Ddu, they are not great in height but are relatively prominent, placed on the western ridge of the latter is Mynydd Ty’n y Fach; a recent deletion from 400m Sub-Pedwarau and a hill whose sudden lack of status could be confirmed by the Trimble.

My first hill of the day was Castell y Bere, I had not previously visited but had wanted to for a long time.  The castle was constructed in the 1220’s by Llywelyn the Great, and as with similar constructions it proceeded to have a turbulent history, and after being besieged in 1294 it fell in to disrepair.

The connecting bwlch for the castle is located in an adjacent field and as the Trimble gathered its allotted data I stood and looked out on the profile of Craig yr Aderyn and its satellite peaks, they rose greened in early summer freshness, rounded and appealing they would lead me toward them in a few days’ time.

Gathering data at the critical bwlch of Castell y Bere

The remains of the castle are an atmospheric place, dominated by near hills it is almost hidden from view by the growth of trees on its lower slopes, and yet it is a place of history, and one that thankfully has not had the misfortune to accumulate a gift shop and kiosk, it sits and stares and stands against the passage of time.

One of two entrance gates to Castell y Bere

When in the castle ruins the ever changing play of light accentuated atmosphere with near hillsides casting light then shade, adding depth and perspective to the landscape.  Surveying its high point was periphery, but once done I retraced my inward steps to the entrance gate and proceeded on my way.

The ruins of Castell y Bere

Castell y Bere with Craig yr Aderyn in the background

A green track leads up the steep westerly slopes of Foel Cae’rberllan and as the morning’s warmth was now creeping across the land, this proved a welcome addition compared to the slight chill earlier in the day, and in time the green track led me to the small grassed and rocky knoll that makes up the summit of this hill.

The shadowed remains of Castell y Bere

Craig yr Aderyn

Gathering data at the summit of Foel Cae'rberllan

Across the intervening Nant yr Eira valley, Foel Ddu rose in a wild looking way, with its upper slopes festooned in tussock grass, between me and it was a steep descent down slopes of bluebells until the grazing fields below were reached.

Foel Ddu with Tal-y-llyn in the background

Graig Goch

My next surveying objective was the connecting bwlch which is placed beside a stone wall; due to prospective satellite disruption I found placing the Trimble atop my rucksack on top of the wall to be the most convenient way to gather data.  This involved a balancing act, but once the offset to the ground below was measured I sat beneath the wall and Trimble and spent a few minutes looking at the beauty of a caterpillar in the undergrowth as it sunned itself.

Gathering data at what I thought to be the critical bwlch of Foel Cae'rberllan

This little creature kept me amused when the Trimble was gathering data

LIDAR bwlch image of Foel Cae'rberllan with the white contour showing the position of the natural bwlch as opposed to the red contour showing the position of disturbed ground beside the wall

Another green track led up the lower south-western flank of Foel Ddu and eased passage toward the tussock laden upper part of the hill.  I was soon on top sitting in clumps of bilberry grass as the Trimble gathered data.  The sun shone and although a cooling breeze blew it felt good to be out on the hill, and there were few places where I would have rather been.

The great bulk of Foel Cae'rberllan rising above the Nant yr Eira

Gathering data at the summit of Foel Ddu

Slightly easier passage on the northern side of the fence that follows the western ridge of Foel Ddu led toward the connecting bwlch, and once this was Trimbled I headed for the summit.

As the Trimble gathered data at the summit of Mynydd Ty’n y Fach I looked out to the wild surrounds of the Nant Pencoed, a great expanse of tussock and heather laden bog, it sat quietly tranquil, probably seldom visited except by a farmer.

Gathering data at the summit of Mynydd Ty'n y Fach

The bog laden expanse of Nant Pencoed

Only one hill remained to visit and survey; Craig Ysgiog, the outlier of Foel Ddu, and this gave stunning views down the flat bedded expanse of Dyffryn Dysynni past the rounded profile of Craig yr Aderyn to the coast beyond.

The cairn atop Craig Ysgiog

Dyffryn Dysynni

By now the cloud that had built and then thinned had disappeared and the hills were bathed in late afternoon glow, giving a beautiful colour to the land.  I followed an old path down the hill, only diverting from it when confronted by a grazing heard of Welsh Blacks who looked inquisitively toward me.

The Welsh Blacks

The path led toward the country lane which would lead me back to my car at Llanfihangel-y-Pennant, it had been a good time on the hill with a lazied feel to the late afternoon amongst quiet surrounds in the beautiful upper part of the Dysynni valley.

Llanfihangel-y-Pennant

Survey Result:

Castell y Bere

Summit Height:  65.1m (converted to OSGM15)

Summit Grid Reference:  SH 66760 08524

Bwlch Height:  39.3m (converted to OSGM15)

Bwlch Grid Reference:  SH 66940 08582

Drop:  25.8m

Dominance:  39.68%

Foel Cae’rberllan

Summit Height:  380.1m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 67628 08207 (Trimble GeoXH 6000)

Bwlch Height:  168.3m (LIDAR)

Bwlch Grid Reference:  SH 68815 08306 (LIDAR)

Drop:  211.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  55.73% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Foel Ddu

Summit Height:  448.0m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 69737 09550 (Trimble GeoXH 6000)

Bwlch Height:  319.4m (LIDAR)

Bwlch Grid Reference:  SH 70581 10146 (LIDAR)

Drop:  128.6m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  28.70% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Mynydd Ty’n y Fach

Summit Height:  408.4m (converted to OSGM15)

Summit Grid Reference:  SH 68787 09703

Bwlch Height:  389.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 69043 09685

Drop:  18.9m (400m Sub-Pedwar deletion)

Dominance:  4.63%

Craig Ysgiog

Summit Height:  324.8m (converted to OSGM15)

Summit Grid Reference:  SH 68403 10288

Bwlch Height:  306.9m (converted to OSGM15)

Bwlch Grid Reference:  SH 68492 10122

Drop:  17.9m

Dominance:  5.52%

For further details please consult the Trimble Survey Spreadsheet

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

Mynydd Ty’n y Fach (SH 687 097) – 400m Sub-Pedwar deletion

There has been a deletion from the listing of the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

Mynydd Ty'n y Fach (SH 687 097)

The criteria for the list that this deletion applies to are:

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills, with this hill being deleted from the 400m Sub-Pedwar category.  The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format. 

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Mynydd Ty’n y Fach, and it is adjoined to the Cadair Idris range of hills, which are situated in the south-western part of North Wales (Region C1, Sub-Region C1B), and it is positioned between the stream valleys of the Afon Cadair to its west and the Afon Dysynni to its south-east, and has the small community of Abergynolwyn towards the south south-west.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips was published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

Extract from the Ordnance Survey 1:25,000 Explorer map

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 20m of drop, based on the 409m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and an estimated c 389m bwlch height, based on interpolation of 10m contouring between 380m – 390m, and these are the details given the hill when the 1^st edition of the Y Pedwarau, now co-authored by Myrddyn Phillips and Aled Williams was published by Europeaklist in May 2013.

LIDAR image of Mynydd Ty'n y Fach (SH 687 097)

However, it was not until LIDAR became available and the subsequent survey with the Trimble GeoXH 6000 that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

The Trimble GeoXH 6000 gathering data at the summit of Mynydd Ty'n y Fach

Therefore, the deletion of this hill from 400m Sub-Pedwar status is due to LIDAR analysis and a subsequent Trimble GeoXH 6000 survey, resulting in a 408.4m summit height and a 389.5m bwlch height, with these values giving this hill 18.9m of drop, which is insufficient for it to be classified as a 400m Sub-Pedwar.

The full details for the hill are:

Group:  Cadair Idris 

Name:  Mynydd Ty’n y Fach

OS 1:50,000 map:  124

Summit Height:  408.4m (converted to OSGM15)

Summit Grid Reference:  SH 68787 09703

Bwlch Height:  389.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 69047 09685

Drop:  18.9m

For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales reported on Mapping Mountains since the May 2013 publication of the list by Europeaklist please consult the following Change Registers:

Y Pedwarau

Y Pedwarau – 400m Sub-Pedwarau

Y Pedwarau – 390m Sub-Pedwarau

Y Pedwarau – 390m Double Sub-Pedwarau

Myrddyn Phillips and Aled Williams (May 2018)