Mapping Mountains – Significant Height Revisions – 100m Twmpau and Y Trechol – the Dominant Hills of Wales

Llys y Gwynt (SH 779 728)

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height and its location, and the drop of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000, both conducted by Myrddyn Phillips with the latter taking place on the 10^th October 2018.

Llys y Gwynt (SH 779 728)

The criteria for the two lists that this height revision 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, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name of the hill is Llys y Gwynt, and it is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and is positioned with the B5106 to its west, the B5279 to its south and the Afon Conwy (River Conwy) to its east, and has the town of Conwy to its north.

When interpolated heights and drop values were added to the original Welsh 100m P30 list that was published on Geoff Crowder’s v-g.me website, this hill was listed with an estimated c 116m summit height based on interpolation of its uppermost 110m contour ring that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

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

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 analysis for this hill was closely followed by the survey of its summit with the Trimble GeoXH 6000. 

LIDAR image of Llys y Gwynt

The summit height produced by the Trimble GeoXH 6000 survey is 120.6m,  this is a substantial revision when compared to some revised heights, and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new listed summit height is 120.6m and this was produced by surveying with the Trimble GeoXH 6000, this is 4.6m higher than its previously listed height of c 116m which was based on interpolation of its uppermost 110m ring contour that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, however this new height is in accordance with the 5m contouring on OS Maps.

Extract from OSMaps showing an uppermost 120m ring contour

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Carneddau

Name:  Llys y Gwynt

OS 1:50,000 map:  115

Summit Height (New height):  120.6m (converted to OSGM15)

Summit Grid Reference:  SH 77982 72884  

Bwlch Height:  50.7m (LIDAR)

Bwlch Grid Reference:  SH 76137 71943 (LIDAR)

Drop:  70.0m (Trimble summit and LIDAR bwlch)

Dominance:  58.00% (Trimble summit and LIDAR bwlch)

For details on the summit survey of this hill

Myrddyn Phillips (March 2019)

Mapping Mountains – Significant Name Changes – 100m Twmpau and Y Trechol – The Dominant Hills of Wales

Llys y Gwynt (SH 779 728)

There has been a Significant Name Change to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height and its location, and the drop of the hill initially confirmed by LIDAR analysis and its summit height subsequently confirmed by a Trimble GeoXH 6000 survey, both conducted by Myrddyn Phillips with the latter taking place on the 10^th October 2018.

Llys y Gwynt (SH 779 728)

The criteria for the two lists 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, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The hill is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and is positioned with the B5106 to its west, the B5279 to its south and the Afon Conwy (River Conwy) to its east, and has the town of Conwy to its north.

The hill originally appeared in the 100m P30 list on Geoff Crowder’s v-g.me website under the transposed name of Tan-y-bryn, with an accompanying note stating; Name from buildings to the West.

Tan-y-bryn

110c

SH779729

115

17

Name from buildings to the West

 

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.  My preference was to use farm names and put Pen, Bryn or Moel in front of them or as in this instance transpose the name of a farm and use it for that of the hill.  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

As the summit of this hill comprises bounded land the details for it were examined on the Tithe map.  The term Tithe map is generally given to a map of a Welsh or English parish or township and which was prepared after the 1836 Tithe Commutation Act.  This act allowed tithes to be paid in cash rather than goods.  The Tithe maps gave names of owners and occupiers of land in each parish and importantly for place-name research they also included the name of enclosed land.  This enclosed land is usually based on a field system, however not every field is given a name, but many are and especially so in Wales.

Extract from the Tithe map

The enclosed land where the summit of this hill is situated is given the number 222 on the Tithe map, this can be cross referenced against the apportionments; it is these apportionments that give the name of the owner or occupier of the land as well as the name of the land.  The land where the summit of this hill is situated is named as Llys y Gwynt in the apportionments, with the details on the Tithe map appearing in the parish of Caerhun and in the county named as Caernarvonshire [sic].

Extract from the apportionments

Therefore, the name this hill is now listed by in the 100m Twmpau and Y Trehol – The Dominant Hills of Wales is Llys y Gwynt, and this name was derived from the Tithe map.

The full details for the hill are:

Group:  Carneddau

Name:  Llys y Gwynt

Previously Listed Name:  Tan-y-bryn 

  

OS 1:50,000 map:  115

Summit Height:  120.6m (converted to OSGM15)

Summit Grid Reference:  SH 77982 72884

Bwlch Height:  50.7m (LIDAR)

Bwlch Grid Reference:  SH 76137 71943 (LIDAR) 

Drop:  70.0m (Trimble summit and LIDAR bwlch)

Dominance:  58.00% (Trimble summit and LIDAR bwlch)

For details on the summit survey of this hill

Myrddyn Phillips (March 2019)

Mapping Mountains – Trimble Surveys – Carnedd Llywelyn

10.10.18  Llys y Gwynt (SH 779 728)  

Llys y Gwynt (SH 779 728)

Llys y Gwynt is one of a number of smaller heighted hills that lies undisturbed except for the passage of an occasional farmer or hill bagger.  It isn’t dramatic in nature, but does afford extensive views in to the higher eastern Carneddau, albeit its summit is plagued by copious amounts of gorse.

I visited Llys y Gwynt relatively early in the morning having travelled from Nantlle and stopping on route to watch the slender threads of mist as they played across the land beside Llyn Gwynant.  The misted scene again appeared beside Llynnau Mymbyr as delicate wafts ebbed their way upward toward the lower flank of Moel Siabod.  The misted morning foretold a blue skied day ahead.

Llyn Gwynant and Moel Hebog

Public footpaths approach the summit of this hill from the north-west and south-east, and it was the latter I chose having parked my car just off the narrow lane in a field, with the wired fence having been conveniently pulled back enabling a farmer’s vehicle to gain immediate access.

A convenient place to park a car

The field led upward toward the ruined gamekeeper’s house that now looks upon the abandoned scene.  This house must have been a solid stoned edifice built against the elements on the summit area of this hill.  Now ivy has taken hold and the roof is no more.  As I looked in through an open gapped window I heard movement inside, I backed away instinctively wondering if it may be a fox or badger, and a few seconds later caught the silent white flight of a barn owl as it flew overhead.

The summit of Llys y Gwynt is situated just beyond the trees in the centre of the photo

The ruined gamekeepers house on the summit of Llys y Gwynt

The high point of the hill was relatively easy to pinpoint and is situated amongst a large patch of gorse close to the ruined building.  Once the Trimble was set up and gathering data I walked around the house and stood in the sunshine looking out on a quiet land still waking in the morning air.

Gathering data at the summit of Llys y Gwynt

I let the Trimble gather 600 datum points, and after ten minutes closed it down, packed it away and retraced my inward route back to my awaiting car.  During the day I hoped to visit six P30s and two other lower prominence hills, all needed Trimbling with the prospective of a number of summit relocations.  My next hill was such an example; Maes Glas Mawr (SH 768 724) and Clytiau Poethion (SH 763 717).

Survey Result:

Llys y Gwynt (significant name change)

Summit Height:  120.6m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SH 77982 72884

Bwlch Height:  50.7m (LIDAR)

Bwlch Grid Reference:  SH 76137 71943 (LIDAR)

Drop:  70.0m (Trimble summit and LIDAR bwlch)

Dominance:  58.00% (Trimble summit and LIDAR bwlch)

For further details please consult the Trimble Survey Spreadsheet