Mapping Mountains – Hill Reclassifications – 700m Twmpau

Pt. 714.3m (SH 827 359) – 700m Sub-Twmpau addition

There has been an addition to the listing of the 700m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams. 

LIDAR image of Pt. 714.3m (SH 827 359)

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

700m Twmpau - Welsh hills at or above 700m and below 800m in height with 30m minimum drop, with an accompanying sub list entitled the 700m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 700m and below 800m 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.  The list is authored by Myrddyn Phillips and is available to download in Google Doc format from Mapping Mountains.

The 700m Twmpau by Myrddyn Phillips

The hill is being listed by the point (Pt. 714.3m) notation and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor roads to the north, south-west and east, and the A4212 road farther to its north, and has the town of Y Bala towards the east.

When the list that later became known as the 700m Twmpau was first compiled, this hill was not included in the accompanying sub list due to an eye and spirit level survey conducted by John and Anne Nuttall that resulted in 60ft (18.3m) of drop, and it was originally listed with a 712m summit height based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and a 694m bwlch height. 

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.

Therefore, the addition of this hill to 700m Sub-Twmpau status is due to LIDAR analysis, resulting in a 714.3m summit height and a 693.6m bwlch height, with these values giving this hill 20.7m of drop, which is sufficient for it to be classified as a 700m Sub-Twmpau.

 

The full details for the hill are:

Group:  Arenig Fawr

Name:  Pt. 714.3m

OS 1:50,000 map:  124, 125

Summit Height:  714.3m (LIDAR) 

Summit Grid Reference:  SH 82741 35938 (LIDAR) 

Bwlch Height:  693.6m (LIDAR) 

Bwlch Grid Reference:  SH 82725 36128 (LIDAR) 

Drop:  20.7m (LIDAR)

 

Myrddyn Phillips (July 2023)

 

 

  

New Welsh LIDAR - Twmpau, Simms and Dodds

 

New Welsh LIDAR – Twmpau, Simms and Dodds 

The release of new Welsh LIDAR has generated a number of status changes, including the following hills in the listing of Twmpau: 

 

500m Twmpau

Group	Name	Summit (m)	Summit GR	Bwlch (m)	Bwlch GR	Drop (m)	Change
Moelwyn Mawr	Pt. 511.7m	511.7	SH 69325 48552	491.7	SH 69253 48542	20.0	Sub-Twmpau addition
Y Llethr	Pt.551.8m	551.8	SH 66588 32216	531.65	SH 66333 32260	20.1	Sub-Twmpau addition

700m Twmpau

Group	Name	Summit (m)	Summit GR	Bwlch (m)	Bwlch GR	Drop (m)	Change
Arenig Fawr	Pt. 714.3m	714.3	SH 82741 35938	693.6	SH 82725 36128	20.7	Sub-Twmpau addition

The release of these new data has also generated a number of proposed status changes in the listings of the Simms and Dodds, including the following hills:

Simms

Group	Name	Summit (m)	Summit GR	Bwlch (m)	Bwlch GR	Drop (m)	Change
Yr Wyddfa	Y Lliwedd	893.2	SH 62402 53249	872.9	SH 62297 53267	20.3	Subsimm addition
Yr Wyddfa	Lliwedd Bach	819.0	SH 62750 53229	798.5	SH 62695 53204	20.5	Subsimm addition
Arenig Fawr	Pt. 714.3m	714.3	SH 82741 35938	693.6	SH 82725 36128	20.7	Subsimm addition

 

Dodds

Group	Name	Summit (m)	Summit GR	Bwlch (m)	Bwlch GR	Drop (m)	Change
Moelwyn Mawr	Craig Stwlan	568.7	SH 66736 44654	548.65	SH 66695 44714	20.0	Subdodd addition
Moelwyn Mawr	Pt. 511.7m	511.7	SH 69325 48552	491.7	SH 69253 48542	20.0	Subdodd addition
Arenig Fach	Y Ro Lwyd	534.3	SH 76110 50527	513.6	SH 76066 50598	20.7	Subdodd addition
Y Llethr	Garn Fach	559.8	SH 69782 22770	537.95	SH 69894 22881	21.8	Subdodd addition
Y Llethr	Pt.551.8m	551.8	SH 66588 32216	531.65	SH 66333 32260	20.1	Subdodd addition

Myrddyn Phillips and Aled Williams (March 2023)

 

 

Mapping Mountains – Hill Reclassifications – 700m Twmpau

Craig Eigiau (SH 713 654) – 700m Sub-Twmpau addition

There has been an addition to the listing of the 700m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Leica RX1250 survey conducted by Alan Dawson, with a previous Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams having taken place.

Craig Eigiau (SH 713 654)

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

700m Twmpau - Welsh hills at or above 700m and below 800m in height with 30m minimum drop, with an accompanying sub list entitled the 700m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 700m and below 800m 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.  The list is authored by Myrddyn Phillips and is available to download in Google Doc format from Mapping Mountains.

700m Twmpau by Myrddyn Phillips

The name the hill is listed by is Craig Eigiau and it is adjoined to the Carnedd Llywelyn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with a minor road to its east and the B5106 road farther to its east, and has the small community of Tal-y-bont towards the north-east.

When the list that later became known as the 700m Twmpau was first compiled, this hill was not included in the accompanying sub list as it was listed with an estimated c 19m of drop, based on the 735m summit spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 716m bwlch height, based on interpolation of 10 contouring between 710m - 720m. 

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

However, it was not until the Trimble GeoXH 6000 survey that the details for this hill could be accurately re-assessed.  This survey resulted in the hill being included as a 700m Sub-Twmpau.  The hill has now been surveyed by Alan Dawson with the Leica RX1250 and it is the height and position produced from this survey that is being prioritised.

The Trimble GeoXH 6000 gathering data at the summit of Craig Eigiau

Therefore, the addition of this hill to 700m Sub-Twmpau status is due to a Trimble GeoXH 6000 survey and a subsequent Leica RX1250 survey, resulting in a 735.0m summit height and a 714.1m bwlch height, with these values giving this hill 20.9m of drop, which is sufficient for it to be classified as a 700m Sub-Twmpau.

The full details for the hill are:

Group:  Carnedd Llywelyn

Name:  Craig Eigiau

OS 1:50,000 map:  115

Summit Height:  735.0m (converted to OSGM15, Leica RX1250)

Summit Grid Reference:  SH 71315 65425 (Leica RX1250) 

  

Bwlch Height:  714.1m (converted to OSGM15, Leica RX1250)

Bwlch Grid Reference:  SH 71191 65460 (Leica RX1250) 

Drop:  20.9m (Leica RX1250)

Myrddyn Phillips (July 2017)