Mapping Mountains – Summit Relocations – 100m Twmpau

Dinas Dinorwig (SH 549 652)

There has been a Summit Relocation to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips.

Dinas Dinorwig (SH 549 652)

The criteria for the list that this summit relocation applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Dinas Dinorwig and it is adjoined to the Glyder Fawr group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is encircled by an old track to its north and minor roads to its west, south and east, with the B4366 road to its north-west and the A4244 road to its north-east, and has the small communities of Bethel towards the west, Rhiwlas towards the east and Llanrug towards the south-west.

Prior to LIDAR analysis this hill was listed with 38m of drop, based on its 170m summit spot height positioned at SH 54966 65306 that appears on the Ordnance Survey 1:25,000 Explorer map (with the 1:50,000 Landranger map giving a 169m summit spot height) and a 132m bwlch height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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

The upper part of this hill comprises an ancient Iron Age Hillfort that has a series of steep embankments and ditches which are in the main overgrown with brambles, bracken and small trees, whilst the inner central part of the upper hill used to be grazed and is now a paddock with an extremely friendly horse when I last visited.  It is this inner central part of the summit area where the 170m spot height is positioned.

LIDAR image of Dinas Dinorwig (SH 549 652)

However, it was not until LIDAR became available 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. 

LIDAR summit image of Dinas Dinorwig (SH 549 652)

The summit height produced by LIDAR analysis is 169.8m and is positioned at SH 54945 65256, this position is to the highest part of the ancient embankments, whereas the height produced by the Trimble GeoXH 6000 to the high point of the inner central part of the hill is 169.2m and is positioned at SH 54964 65301.  As the location of the listed summit of this hill is to a different feature compared to its previously listed summit position this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

The Trimble set-up position with the very friendly horse at the old listed summit position of Dinas Dinorwig

Therefore, the height produced by LIDAR analysis to the summit of this hill is 169.8m and this is positioned at SH 54945 65256, this position is approximately 50 metres southward from where the 170m spot height appears on the contemporary Ordnance Survey 1:25,000 Explorer map and which was surveyed as being 169.2m in height, and importantly the new summit position is to a different feature.

The summit of Dinas Dinorwig

The full details for the hill are:

Group:  Glyder Fawr

Name:  Dinas Dinorwig

OS 1:50,000 map:  114, 115

Summit Height:  169.8m (LIDAR)

Summit Grid Reference (New Position):  SH 54945 65256 (LIDAR)

Bwlch Height:  131.8m (LIDAR)

Bwlch Grid Reference:  SH 54642 64647 (LIDAR) 

Drop:  38.1m (LIDAR)

Myrddyn Phillips (March 2019)

Mapping Mountains – Significant Name Changes – 100m Twmpau

Dinas Dinorwig (SN 549 652)

There has been a Significant Name Change to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips.

Dinas Dinorwig (SH 549 652)

The criteria for the list that this name change applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

100m Twmpau by Myrddyn Phillips

The hill is adjoined to the Glyder Fawr group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is encircled by an old track to its north and minor roads to its west, south and east, with the B4366 road to its north-west and the A4244 road to its north-east, and has the small communities of Bethel towards the west, Rhiwlas towards the east and Llanrug towards the south-west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill appeared under the transposed name of Pen Dinas, with an accompanying note stating; aka Dinas Dinorwig.

Pen Dinas

170m

SH549653

114/115

17/263

aka Dinas Dinorwig

During my early hill listing I thought it appropriate to either invent a name for a hill, or use a name that appeared near to the summit of the hill on Ordnance Survey maps of the day, with little consideration for the meaning of the name and where it was appropriately applied to.  My preference was to use farm names and put Pen, Bryn or Moel in front of them or as in this instance use what I thought was the name of the hill and which unbeknownst to me at the time, is the name of a farm.  This is not a practice that I now advocate as with time and inclination place-name data can be improved either by asking local people or by examining historic documents, through this form of research an appropriate name for the hill can usually be found.

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

The summit of this hill has an ancient Iron Age Hillfort positioned on it which is known as Dinas Dinorwig, and it is this structure that gives its listed name to the hill, whereas although the name of Pen Dinas is evident on contemporary Ordnance Survey maps this name is that of a farm situated close to the summit and not the name of the hill itself.

The sign on the gate leading to Pendinas Farm

Therefore, as an appropriate name for the hill already exists on contemporary Ordnance Survey maps this hill is now listed as Dinas Dinorwig in the 100m Twmpau.

The full details for the hill are:

Group:  Glyder Fawr

Name:  Dinas Dinorwig

Previously Listed Name:  Pen Dinas 

OS 1:50,000 map:  114, 115

Summit Height:  169.8m (LIDAR)

Summit Grid Reference:  SH 54945 65256 (LIDAR)

Bwlch Height:  131.8m (LIDAR)

Bwlch Grid Reference:  SH 54642 64647 (LIDAR) 

Drop:  38.1m (LIDAR)

Myrddyn Phillips (March 2019)

Mapping Mountains – Trimble Surveys – Glyder Fawr

06.10.18  Dinas Dinorwig (SH 549 652)  

Dinas Dinorwig (SH 549 652)

Dinas Dinorwig is a part of the Glyderau lowlands as them succumb to grazed fields and eventually the sea.  The hill is situated near the small community of Bethel and as its name implies the upper part of the hill has the remains of an ancient Iron Age hill fort on it with the ramparts now infested by small trees, brambles and high bracken, making the hill well protected from prospective visitors.

I’d visited once before in May 2004 when the hill was listed as Pen Dinas, which is the name of the farm nestled below the northern part of the upper ramparts.

Prior to my second visit I analysed the summit and bwlch of this hill with LIDAR, and found that the contouring give a part of the upper ramparts as higher than the grazed inner part of the hill which is crowned by two rocks on what looks like a slightly raised old grassed cairn.

As the ancient ramparts and their brambled and brackened defences would give a testing ascent I thought enquiring at Pen Dinas if I could park and use a path beside the farm to visit the summit would be a more convenient approach.  As no one answered when I knocked on the door I parked my car, left a note on the dashboard explaining where I had gone and who I was, and up I went with Trimble in hand.

A grassed path led around the side of the farm through the upper rampart to what I expected to be a grazed inner part of the hill, I was surprised to be met by a friendly horse that now has the run of this part of the hill as a paddock.

I wondered how the horse would react with a surveyor wandering in his domain; I should not have worried as the horse remained inquisitive and very friendly during my stay in his paddock.  After gently talking to and stroking the horse we seemed on best of terms.

The high point of this part of the hill was easy to determine and as I set the Trimble up the horse showed more interest in what I was doing than many of my hill walking friends.  Once the equipment was in position I slowly backed away and hoped the horse would follow, thankfully it was now more interested in me than the Trimble and off we sauntered to the edge of the paddock, and during data collection the horse remained close nuzzling its head toward me on occasion.

My new surveying assistant

I now wanted to take a data set from where LIDAR gives the summit of the hill to be situated, but all I could see was a mass of bramble and undergrowth.  I gave up on my first venture in to this almost impenetrable jungle and decided to approach from a slightly different direction; I was soon standing in bracken that was well above my head, a novel experience to say the least.  I wondered what the horse was making of it all.

As I slowly waded through the undergrowth the first signs of an embankment came in to view, this was no more than a rise of bramble and stunted trees, but there was something definitely there, I struggled on and eventually clambered up on to one of the inner ramparts and looked steeply down to a ditch, which again was swamped in all manner of undergrowth.

Somewhere up there is the summit of Dinas Dinorwig

I checked the grid reference on the Trimble’s screen against the summit position from LIDAR and stretched out a boot cladded foot to touch the highest part of ground which was under a stunted tree and more bramble and looked at where I was now standing, deciding that it would be next to impossible to set the Trimble up let alone gather data from this position I decided that LIDAR alone would suffice for the position and height of this hill’s summit.

On top of the ancient embankment

As I clambered down from the rampart I was met by what I initially thought to be a swarm of flies, they were diffused in late afternoon sunlight, their small silhouettes difficult to detail, but I became aware that they were yellow as one landed on my fleece coat, I’d disturbed a bee’s nest and they were not happy.  As I looked at the bee on my coat which was just under my chin I felt a sharp pain in my upper right arm, one had stung me, I wondered if it was under my fleece or had gone for the direct approach landing on my fleeced arm and attacking me from there.  Whatever its approach I did not hang around and quickly left the undergrowth and the bees to their own devices.  The thought of attempting to gather Trimble data from the embankment was now a definite non-starter!

Before leaving I went back to the rock in the centre of the paddock and compared the grid reference for its position against that produced by LIDAR, and again the horse sauntered toward me and inspected the Trimble, a gentle soul who I patted my goodbye’s to before walking the short distance to the farm and my awaiting car, rubbing my right arm as I did so.

Survey Result:

Dinas Dinorwig (significant name change)

Summit Height:  169.8m (LIDAR)

Summit Grid Reference:  SH 54945 65256 (LIDAR) (summit relocation)

Bwlch Height:  131.8m (LIDAR)

Bwlch Grid Reference:  SH 54642 64647 (LIDAR)

Drop:  38.1m (LIDAR)

Dominance:  22.41% (LIDAR)

For further details please consult the Trimble Survey Spreadsheet